[PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Song Liu]

As Miklos reported and suggested:

  This pattern repeats two times in trace_uprobe.c and in
  kernel/events/core.c as well:

      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
      if (ret)
          goto fail_address_parse;

      inode = igrab(d_inode(path.dentry));
      path_put(&path);

  And it's wrong.  You can only hold a reference to the inode if you
  have an active ref to the superblock as well (which is normally
  through path.mnt) or holding s_umount.

  This way unmounting the containing filesystem while the tracepoint is
  active will give you the "VFS: Busy inodes after unmount..." message
  and a crash when the inode is finally put.

  Solution: store path instead of inode.

This patch fixes two instances in trace_uprobe.c.

Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Howard McLauchlan <hmclauchlan@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------
 1 file changed, 16 insertions(+), 33 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 34fd0e0..d9ee522c 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -55,7 +55,7 @@ struct trace_uprobe {
 	struct list_head		list;
 	struct trace_uprobe_filter	filter;
 	struct uprobe_consumer		consumer;
-	struct inode			*inode;
+	struct path			path;
 	char				*filename;
 	unsigned long			offset;
 	unsigned long			nhit;
@@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
 	for (i = 0; i < tu->tp.nr_args; i++)
 		traceprobe_free_probe_arg(&tu->tp.args[i]);
 
-	iput(tu->inode);
+	path_put(&tu->path);
 	kfree(tu->tp.call.class->system);
 	kfree(tu->tp.call.name);
 	kfree(tu->filename);
@@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
 static int create_trace_uprobe(int argc, char **argv)
 {
 	struct trace_uprobe *tu;
-	struct inode *inode;
 	char *arg, *event, *group, *filename;
 	char buf[MAX_EVENT_NAME_LEN];
 	struct path path;
@@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
 	bool is_delete, is_return;
 	int i, ret;
 
-	inode = NULL;
 	ret = 0;
 	is_delete = false;
 	is_return = false;
@@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv)
 	}
 	/* Find the last occurrence, in case the path contains ':' too. */
 	arg = strrchr(argv[1], ':');
-	if (!arg) {
-		ret = -EINVAL;
-		goto fail_address_parse;
-	}
+	if (!arg)
+		return -EINVAL;
 
 	*arg++ = '\0';
 	filename = argv[1];
 	ret = kern_path(filename, LOOKUP_FOLLOW, &path);
 	if (ret)
-		goto fail_address_parse;
-
-	inode = igrab(d_real_inode(path.dentry));
-	path_put(&path);
-
-	if (!inode || !S_ISREG(inode->i_mode)) {
-		ret = -EINVAL;
-		goto fail_address_parse;
-	}
+		return ret;
 
 	ret = kstrtoul(arg, 0, &offset);
 	if (ret)
@@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv)
 		goto fail_address_parse;
 	}
 	tu->offset = offset;
-	tu->inode = inode;
+	tu->path = path;
 	tu->filename = kstrdup(filename, GFP_KERNEL);
 
 	if (!tu->filename) {
@@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv)
 	return ret;
 
 fail_address_parse:
-	iput(inode);
+	path_put(&path);
 
 	pr_info("Failed to parse address or file.\n");
 
@@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
 		goto err_flags;
 
 	tu->consumer.filter = filter;
-	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
+	ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
+			      &tu->consumer);
 	if (ret)
 		goto err_buffer;
 
@@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
 
 	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
 
-	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
+	uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
 	tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
 
 	uprobe_buffer_disable();
@@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
 	write_unlock(&tu->filter.rwlock);
 
 	if (!done)
-		return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
+		return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
+				    &tu->consumer, false);
 
 	return 0;
 }
@@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
 
 	err = 0;
 	if (!done) {
-		err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
+		err = uprobe_apply(d_inode(tu->path.dentry),
+				   tu->offset, &tu->consumer, true);
 		if (err)
 			uprobe_perf_close(tu, event);
 	}
@@ -1337,7 +1328,6 @@ struct trace_event_call *
 create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 {
 	struct trace_uprobe *tu;
-	struct inode *inode;
 	struct path path;
 	int ret;
 
@@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 	if (ret)
 		return ERR_PTR(ret);
 
-	inode = igrab(d_inode(path.dentry));
-	path_put(&path);
-
-	if (!inode || !S_ISREG(inode->i_mode)) {
-		iput(inode);
-		return ERR_PTR(-EINVAL);
-	}
-
 	/*
 	 * local trace_kprobes are not added to probe_list, so they are never
 	 * searched in find_trace_kprobe(). Therefore, there is no concern of
@@ -1364,11 +1346,12 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 	if (IS_ERR(tu)) {
 		pr_info("Failed to allocate trace_uprobe.(%d)\n",
 			(int)PTR_ERR(tu));
+		path_put(&path);
 		return ERR_CAST(tu);
 	}
 
 	tu->offset = offs;
-	tu->inode = inode;
+	tu->path = path;
 	tu->filename = kstrdup(name, GFP_KERNEL);
 	init_trace_event_call(tu, &tu->tp.call);
 
-- 
2.9.5

Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Steven Rostedt]

You forgot to add Miklos again.

Miklos, have any comments on this patch? Or can you give a
"Reviewed-by"?

-- Steve


On Wed, 18 Apr 2018 10:40:14 -0700
Song Liu <songliubraving@fb.com> wrote:

> As Miklos reported and suggested:
> 
>   This pattern repeats two times in trace_uprobe.c and in
>   kernel/events/core.c as well:
> 
>       ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>       if (ret)
>           goto fail_address_parse;
> 
>       inode = igrab(d_inode(path.dentry));
>       path_put(&path);
> 
>   And it's wrong.  You can only hold a reference to the inode if you
>   have an active ref to the superblock as well (which is normally
>   through path.mnt) or holding s_umount.
> 
>   This way unmounting the containing filesystem while the tracepoint is
>   active will give you the "VFS: Busy inodes after unmount..." message
>   and a crash when the inode is finally put.
> 
>   Solution: store path instead of inode.
> 
> This patch fixes two instances in trace_uprobe.c.
> 
> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Howard McLauchlan <hmclauchlan@fb.com>
> Cc: Josef Bacik <jbacik@fb.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------
>  1 file changed, 16 insertions(+), 33 deletions(-)
> 
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 34fd0e0..d9ee522c 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -55,7 +55,7 @@ struct trace_uprobe {
>  	struct list_head		list;
>  	struct trace_uprobe_filter	filter;
>  	struct uprobe_consumer		consumer;
> -	struct inode			*inode;
> +	struct path			path;
>  	char				*filename;
>  	unsigned long			offset;
>  	unsigned long			nhit;
> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>  	for (i = 0; i < tu->tp.nr_args; i++)
>  		traceprobe_free_probe_arg(&tu->tp.args[i]);
>  
> -	iput(tu->inode);
> +	path_put(&tu->path);
>  	kfree(tu->tp.call.class->system);
>  	kfree(tu->tp.call.name);
>  	kfree(tu->filename);
> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>  static int create_trace_uprobe(int argc, char **argv)
>  {
>  	struct trace_uprobe *tu;
> -	struct inode *inode;
>  	char *arg, *event, *group, *filename;
>  	char buf[MAX_EVENT_NAME_LEN];
>  	struct path path;
> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>  	bool is_delete, is_return;
>  	int i, ret;
>  
> -	inode = NULL;
>  	ret = 0;
>  	is_delete = false;
>  	is_return = false;
> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv)
>  	}
>  	/* Find the last occurrence, in case the path contains ':' too. */
>  	arg = strrchr(argv[1], ':');
> -	if (!arg) {
> -		ret = -EINVAL;
> -		goto fail_address_parse;
> -	}
> +	if (!arg)
> +		return -EINVAL;
>  
>  	*arg++ = '\0';
>  	filename = argv[1];
>  	ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>  	if (ret)
> -		goto fail_address_parse;
> -
> -	inode = igrab(d_real_inode(path.dentry));
> -	path_put(&path);
> -
> -	if (!inode || !S_ISREG(inode->i_mode)) {
> -		ret = -EINVAL;
> -		goto fail_address_parse;
> -	}
> +		return ret;
>  
>  	ret = kstrtoul(arg, 0, &offset);
>  	if (ret)
> @@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv)
>  		goto fail_address_parse;
>  	}
>  	tu->offset = offset;
> -	tu->inode = inode;
> +	tu->path = path;
>  	tu->filename = kstrdup(filename, GFP_KERNEL);
>  
>  	if (!tu->filename) {
> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv)
>  	return ret;
>  
>  fail_address_parse:
> -	iput(inode);
> +	path_put(&path);
>  
>  	pr_info("Failed to parse address or file.\n");
>  
> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>  		goto err_flags;
>  
>  	tu->consumer.filter = filter;
> -	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> +	ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
> +			      &tu->consumer);
>  	if (ret)
>  		goto err_buffer;
>  
> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>  
>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>  
> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> +	uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>  	tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>  
>  	uprobe_buffer_disable();
> @@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>  	write_unlock(&tu->filter.rwlock);
>  
>  	if (!done)
> -		return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
> +		return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
> +				    &tu->consumer, false);
>  
>  	return 0;
>  }
> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>  
>  	err = 0;
>  	if (!done) {
> -		err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
> +		err = uprobe_apply(d_inode(tu->path.dentry),
> +				   tu->offset, &tu->consumer, true);
>  		if (err)
>  			uprobe_perf_close(tu, event);
>  	}
> @@ -1337,7 +1328,6 @@ struct trace_event_call *
>  create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  {
>  	struct trace_uprobe *tu;
> -	struct inode *inode;
>  	struct path path;
>  	int ret;
>  
> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  	if (ret)
>  		return ERR_PTR(ret);
>  
> -	inode = igrab(d_inode(path.dentry));
> -	path_put(&path);
> -
> -	if (!inode || !S_ISREG(inode->i_mode)) {
> -		iput(inode);
> -		return ERR_PTR(-EINVAL);
> -	}
> -
>  	/*
>  	 * local trace_kprobes are not added to probe_list, so they are never
>  	 * searched in find_trace_kprobe(). Therefore, there is no concern of
> @@ -1364,11 +1346,12 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  	if (IS_ERR(tu)) {
>  		pr_info("Failed to allocate trace_uprobe.(%d)\n",
>  			(int)PTR_ERR(tu));
> +		path_put(&path);
>  		return ERR_CAST(tu);
>  	}
>  
>  	tu->offset = offs;
> -	tu->inode = inode;
> +	tu->path = path;
>  	tu->filename = kstrdup(name, GFP_KERNEL);
>  	init_trace_event_call(tu, &tu->tp.call);
>  

Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Song Liu]

> On Apr 18, 2018, at 10:47 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> You forgot to add Miklos again.
> 

I am really sorry! I was expecting "Reported-by" to add Miklos.

Song


> Miklos, have any comments on this patch? Or can you give a
> "Reviewed-by"?
> 
> -- Steve
> 
> 
> On Wed, 18 Apr 2018 10:40:14 -0700
> Song Liu <songliubraving@fb.com> wrote:
> 
>> As Miklos reported and suggested:
>> 
>>  This pattern repeats two times in trace_uprobe.c and in
>>  kernel/events/core.c as well:
>> 
>>      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>      if (ret)
>>          goto fail_address_parse;
>> 
>>      inode = igrab(d_inode(path.dentry));
>>      path_put(&path);
>> 
>>  And it's wrong.  You can only hold a reference to the inode if you
>>  have an active ref to the superblock as well (which is normally
>>  through path.mnt) or holding s_umount.
>> 
>>  This way unmounting the containing filesystem while the tracepoint is
>>  active will give you the "VFS: Busy inodes after unmount..." message
>>  and a crash when the inode is finally put.
>> 
>>  Solution: store path instead of inode.
>> 
>> This patch fixes two instances in trace_uprobe.c.
>> 
>> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
>> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Howard McLauchlan <hmclauchlan@fb.com>
>> Cc: Josef Bacik <jbacik@fb.com>
>> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>> kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------
>> 1 file changed, 16 insertions(+), 33 deletions(-)
>> 
>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>> index 34fd0e0..d9ee522c 100644
>> --- a/kernel/trace/trace_uprobe.c
>> +++ b/kernel/trace/trace_uprobe.c
>> @@ -55,7 +55,7 @@ struct trace_uprobe {
>> 	struct list_head		list;
>> 	struct trace_uprobe_filter	filter;
>> 	struct uprobe_consumer		consumer;
>> -	struct inode			*inode;
>> +	struct path			path;
>> 	char				*filename;
>> 	unsigned long			offset;
>> 	unsigned long			nhit;
>> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>> 	for (i = 0; i < tu->tp.nr_args; i++)
>> 		traceprobe_free_probe_arg(&tu->tp.args[i]);
>> 
>> -	iput(tu->inode);
>> +	path_put(&tu->path);
>> 	kfree(tu->tp.call.class->system);
>> 	kfree(tu->tp.call.name);
>> 	kfree(tu->filename);
>> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>> static int create_trace_uprobe(int argc, char **argv)
>> {
>> 	struct trace_uprobe *tu;
>> -	struct inode *inode;
>> 	char *arg, *event, *group, *filename;
>> 	char buf[MAX_EVENT_NAME_LEN];
>> 	struct path path;
>> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>> 	bool is_delete, is_return;
>> 	int i, ret;
>> 
>> -	inode = NULL;
>> 	ret = 0;
>> 	is_delete = false;
>> 	is_return = false;
>> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv)
>> 	}
>> 	/* Find the last occurrence, in case the path contains ':' too. */
>> 	arg = strrchr(argv[1], ':');
>> -	if (!arg) {
>> -		ret = -EINVAL;
>> -		goto fail_address_parse;
>> -	}
>> +	if (!arg)
>> +		return -EINVAL;
>> 
>> 	*arg++ = '\0';
>> 	filename = argv[1];
>> 	ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>> 	if (ret)
>> -		goto fail_address_parse;
>> -
>> -	inode = igrab(d_real_inode(path.dentry));
>> -	path_put(&path);
>> -
>> -	if (!inode || !S_ISREG(inode->i_mode)) {
>> -		ret = -EINVAL;
>> -		goto fail_address_parse;
>> -	}
>> +		return ret;
>> 
>> 	ret = kstrtoul(arg, 0, &offset);
>> 	if (ret)
>> @@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv)
>> 		goto fail_address_parse;
>> 	}
>> 	tu->offset = offset;
>> -	tu->inode = inode;
>> +	tu->path = path;
>> 	tu->filename = kstrdup(filename, GFP_KERNEL);
>> 
>> 	if (!tu->filename) {
>> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv)
>> 	return ret;
>> 
>> fail_address_parse:
>> -	iput(inode);
>> +	path_put(&path);
>> 
>> 	pr_info("Failed to parse address or file.\n");
>> 
>> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>> 		goto err_flags;
>> 
>> 	tu->consumer.filter = filter;
>> -	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>> +	ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
>> +			      &tu->consumer);
>> 	if (ret)
>> 		goto err_buffer;
>> 
>> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>> 
>> 	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>> 
>> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>> +	uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>> 	tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>> 
>> 	uprobe_buffer_disable();
>> @@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>> 	write_unlock(&tu->filter.rwlock);
>> 
>> 	if (!done)
>> -		return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
>> +		return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
>> +				    &tu->consumer, false);
>> 
>> 	return 0;
>> }
>> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>> 
>> 	err = 0;
>> 	if (!done) {
>> -		err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
>> +		err = uprobe_apply(d_inode(tu->path.dentry),
>> +				   tu->offset, &tu->consumer, true);
>> 		if (err)
>> 			uprobe_perf_close(tu, event);
>> 	}
>> @@ -1337,7 +1328,6 @@ struct trace_event_call *
>> create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>> {
>> 	struct trace_uprobe *tu;
>> -	struct inode *inode;
>> 	struct path path;
>> 	int ret;
>> 
>> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>> 	if (ret)
>> 		return ERR_PTR(ret);
>> 
>> -	inode = igrab(d_inode(path.dentry));
>> -	path_put(&path);
>> -
>> -	if (!inode || !S_ISREG(inode->i_mode)) {
>> -		iput(inode);
>> -		return ERR_PTR(-EINVAL);
>> -	}
>> -
>> 	/*
>> 	 * local trace_kprobes are not added to probe_list, so they are never
>> 	 * searched in find_trace_kprobe(). Therefore, there is no concern of
>> @@ -1364,11 +1346,12 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>> 	if (IS_ERR(tu)) {
>> 		pr_info("Failed to allocate trace_uprobe.(%d)\n",
>> 			(int)PTR_ERR(tu));
>> +		path_put(&path);
>> 		return ERR_CAST(tu);
>> 	}
>> 
>> 	tu->offset = offs;
>> -	tu->inode = inode;
>> +	tu->path = path;
>> 	tu->filename = kstrdup(name, GFP_KERNEL);
>> 	init_trace_event_call(tu, &tu->tp.call);
>> 
> 

Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Miklos Szeredi]

On Wed, Apr 18, 2018 at 7:40 PM, Song Liu <songliubraving@fb.com> wrote:
> As Miklos reported and suggested:
>
>   This pattern repeats two times in trace_uprobe.c and in
>   kernel/events/core.c as well:
>
>       ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>       if (ret)
>           goto fail_address_parse;
>
>       inode = igrab(d_inode(path.dentry));
>       path_put(&path);
>
>   And it's wrong.  You can only hold a reference to the inode if you
>   have an active ref to the superblock as well (which is normally
>   through path.mnt) or holding s_umount.
>
>   This way unmounting the containing filesystem while the tracepoint is
>   active will give you the "VFS: Busy inodes after unmount..." message
>   and a crash when the inode is finally put.
>
>   Solution: store path instead of inode.
>
> This patch fixes two instances in trace_uprobe.c.
>
> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Howard McLauchlan <hmclauchlan@fb.com>
> Cc: Josef Bacik <jbacik@fb.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------
>  1 file changed, 16 insertions(+), 33 deletions(-)
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 34fd0e0..d9ee522c 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -55,7 +55,7 @@ struct trace_uprobe {
>         struct list_head                list;
>         struct trace_uprobe_filter      filter;
>         struct uprobe_consumer          consumer;
> -       struct inode                    *inode;
> +       struct path                     path;
>         char                            *filename;
>         unsigned long                   offset;
>         unsigned long                   nhit;
> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>         for (i = 0; i < tu->tp.nr_args; i++)
>                 traceprobe_free_probe_arg(&tu->tp.args[i]);
>
> -       iput(tu->inode);
> +       path_put(&tu->path);
>         kfree(tu->tp.call.class->system);
>         kfree(tu->tp.call.name);
>         kfree(tu->filename);
> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>  static int create_trace_uprobe(int argc, char **argv)
>  {
>         struct trace_uprobe *tu;
> -       struct inode *inode;
>         char *arg, *event, *group, *filename;
>         char buf[MAX_EVENT_NAME_LEN];
>         struct path path;
> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>         bool is_delete, is_return;
>         int i, ret;
>
> -       inode = NULL;
>         ret = 0;
>         is_delete = false;
>         is_return = false;
> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv)
>         }
>         /* Find the last occurrence, in case the path contains ':' too. */
>         arg = strrchr(argv[1], ':');
> -       if (!arg) {
> -               ret = -EINVAL;
> -               goto fail_address_parse;
> -       }
> +       if (!arg)
> +               return -EINVAL;
>
>         *arg++ = '\0';
>         filename = argv[1];
>         ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>         if (ret)
> -               goto fail_address_parse;
> -
> -       inode = igrab(d_real_inode(path.dentry));
> -       path_put(&path);
> -
> -       if (!inode || !S_ISREG(inode->i_mode)) {

Where has the S_ISREG check gone?

> -               ret = -EINVAL;
> -               goto fail_address_parse;
> -       }
> +               return ret;
>
>         ret = kstrtoul(arg, 0, &offset);
>         if (ret)
> @@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv)
>                 goto fail_address_parse;
>         }
>         tu->offset = offset;
> -       tu->inode = inode;
> +       tu->path = path;
>         tu->filename = kstrdup(filename, GFP_KERNEL);
>
>         if (!tu->filename) {
> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv)
>         return ret;
>
>  fail_address_parse:
> -       iput(inode);
> +       path_put(&path);
>
>         pr_info("Failed to parse address or file.\n");
>
> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>                 goto err_flags;
>
>         tu->consumer.filter = filter;
> -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
> +                             &tu->consumer);
>         if (ret)
>                 goto err_buffer;
>
> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>
>         WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>
> -       uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> +       uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>         tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>
>         uprobe_buffer_disable();
> @@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>         write_unlock(&tu->filter.rwlock);
>
>         if (!done)
> -               return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
> +               return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
> +                                   &tu->consumer, false);
>
>         return 0;
>  }
> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>
>         err = 0;
>         if (!done) {
> -               err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
> +               err = uprobe_apply(d_inode(tu->path.dentry),
> +                                  tu->offset, &tu->consumer, true);
>                 if (err)
>                         uprobe_perf_close(tu, event);
>         }
> @@ -1337,7 +1328,6 @@ struct trace_event_call *
>  create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  {
>         struct trace_uprobe *tu;
> -       struct inode *inode;
>         struct path path;
>         int ret;
>
> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>         if (ret)
>                 return ERR_PTR(ret);
>
> -       inode = igrab(d_inode(path.dentry));
> -       path_put(&path);
> -
> -       if (!inode || !S_ISREG(inode->i_mode)) {

And here, again.

Otherwise ACK.

Also please create a separate patch that removes igrab/iput calls from
kernel/events/uprobes.c and adds a comment to the effect that the
caller is required to keep the inode (and the containing mount)
referenced.

Thanks,
Miklos

Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Miklos Szeredi]

On Thu, Apr 19, 2018 at 10:58 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Wed, Apr 18, 2018 at 7:40 PM, Song Liu <songliubraving@fb.com> wrote:
>> As Miklos reported and suggested:
>>
>>   This pattern repeats two times in trace_uprobe.c and in
>>   kernel/events/core.c as well:
>>
>>       ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>       if (ret)
>>           goto fail_address_parse;
>>
>>       inode = igrab(d_inode(path.dentry));
>>       path_put(&path);
>>
>>   And it's wrong.  You can only hold a reference to the inode if you
>>   have an active ref to the superblock as well (which is normally
>>   through path.mnt) or holding s_umount.
>>
>>   This way unmounting the containing filesystem while the tracepoint is
>>   active will give you the "VFS: Busy inodes after unmount..." message
>>   and a crash when the inode is finally put.
>>
>>   Solution: store path instead of inode.
>>
>> This patch fixes two instances in trace_uprobe.c.
>>
>> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
>> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Howard McLauchlan <hmclauchlan@fb.com>
>> Cc: Josef Bacik <jbacik@fb.com>
>> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>>  kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------
>>  1 file changed, 16 insertions(+), 33 deletions(-)
>>
>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>> index 34fd0e0..d9ee522c 100644
>> --- a/kernel/trace/trace_uprobe.c
>> +++ b/kernel/trace/trace_uprobe.c
>> @@ -55,7 +55,7 @@ struct trace_uprobe {
>>         struct list_head                list;
>>         struct trace_uprobe_filter      filter;
>>         struct uprobe_consumer          consumer;
>> -       struct inode                    *inode;
>> +       struct path                     path;
>>         char                            *filename;
>>         unsigned long                   offset;
>>         unsigned long                   nhit;
>> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>>         for (i = 0; i < tu->tp.nr_args; i++)
>>                 traceprobe_free_probe_arg(&tu->tp.args[i]);
>>
>> -       iput(tu->inode);
>> +       path_put(&tu->path);
>>         kfree(tu->tp.call.class->system);
>>         kfree(tu->tp.call.name);
>>         kfree(tu->filename);
>> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>>  static int create_trace_uprobe(int argc, char **argv)
>>  {
>>         struct trace_uprobe *tu;
>> -       struct inode *inode;
>>         char *arg, *event, *group, *filename;
>>         char buf[MAX_EVENT_NAME_LEN];
>>         struct path path;
>> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>>         bool is_delete, is_return;
>>         int i, ret;
>>
>> -       inode = NULL;
>>         ret = 0;
>>         is_delete = false;
>>         is_return = false;
>> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv)
>>         }
>>         /* Find the last occurrence, in case the path contains ':' too. */
>>         arg = strrchr(argv[1], ':');
>> -       if (!arg) {
>> -               ret = -EINVAL;
>> -               goto fail_address_parse;
>> -       }
>> +       if (!arg)
>> +               return -EINVAL;
>>
>>         *arg++ = '\0';
>>         filename = argv[1];
>>         ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>         if (ret)
>> -               goto fail_address_parse;
>> -
>> -       inode = igrab(d_real_inode(path.dentry));

Also, where has the d_real_inode() gone?

Looks like we need tu->inode back, since the return value of
d_real_inode() may change over time.   I'd do the "tu->inode =
d_real_inode(tu->path.dentry)" just before first use (i.e. when
enabling the tracepoint).

Thanks,
Miklos


>> -       path_put(&path);
>> -
>> -       if (!inode || !S_ISREG(inode->i_mode)) {
>
> Where has the S_ISREG check gone?
>
>> -               ret = -EINVAL;
>> -               goto fail_address_parse;
>> -       }
>> +               return ret;
>>
>>         ret = kstrtoul(arg, 0, &offset);
>>         if (ret)
>> @@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv)
>>                 goto fail_address_parse;
>>         }
>>         tu->offset = offset;
>> -       tu->inode = inode;
>> +       tu->path = path;
>>         tu->filename = kstrdup(filename, GFP_KERNEL);
>>
>>         if (!tu->filename) {
>> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv)
>>         return ret;
>>
>>  fail_address_parse:
>> -       iput(inode);
>> +       path_put(&path);
>>
>>         pr_info("Failed to parse address or file.\n");
>>
>> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>>                 goto err_flags;
>>
>>         tu->consumer.filter = filter;
>> -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>> +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
>> +                             &tu->consumer);
>>         if (ret)
>>                 goto err_buffer;
>>
>> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>>
>>         WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>>
>> -       uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>> +       uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>>         tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>>
>>         uprobe_buffer_disable();
>> @@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>>         write_unlock(&tu->filter.rwlock);
>>
>>         if (!done)
>> -               return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
>> +               return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
>> +                                   &tu->consumer, false);
>>
>>         return 0;
>>  }
>> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>>
>>         err = 0;
>>         if (!done) {
>> -               err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
>> +               err = uprobe_apply(d_inode(tu->path.dentry),
>> +                                  tu->offset, &tu->consumer, true);
>>                 if (err)
>>                         uprobe_perf_close(tu, event);
>>         }
>> @@ -1337,7 +1328,6 @@ struct trace_event_call *
>>  create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>>  {
>>         struct trace_uprobe *tu;
>> -       struct inode *inode;
>>         struct path path;
>>         int ret;
>>
>> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>>         if (ret)
>>                 return ERR_PTR(ret);
>>
>> -       inode = igrab(d_inode(path.dentry));
>> -       path_put(&path);
>> -
>> -       if (!inode || !S_ISREG(inode->i_mode)) {
>
> And here, again.
>
> Otherwise ACK.
>
> Also please create a separate patch that removes igrab/iput calls from
> kernel/events/uprobes.c and adds a comment to the effect that the
> caller is required to keep the inode (and the containing mount)
> referenced.
>
> Thanks,
> Miklos

Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Song Liu]

> On Apr 19, 2018, at 7:44 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> 
> On Thu, Apr 19, 2018 at 10:58 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>> On Wed, Apr 18, 2018 at 7:40 PM, Song Liu <songliubraving@fb.com> wrote:
>>> As Miklos reported and suggested:
>>> 
>>>  This pattern repeats two times in trace_uprobe.c and in
>>>  kernel/events/core.c as well:
>>> 
>>>      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>>      if (ret)
>>>          goto fail_address_parse;
>>> 
>>>      inode = igrab(d_inode(path.dentry));
>>>      path_put(&path);
>>> 
>>>  And it's wrong.  You can only hold a reference to the inode if you
>>>  have an active ref to the superblock as well (which is normally
>>>  through path.mnt) or holding s_umount.
>>> 
>>>  This way unmounting the containing filesystem while the tracepoint is
>>>  active will give you the "VFS: Busy inodes after unmount..." message
>>>  and a crash when the inode is finally put.
>>> 
>>>  Solution: store path instead of inode.
>>> 
>>> This patch fixes two instances in trace_uprobe.c.
>>> 
>>> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
>>> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
>>> Cc: Steven Rostedt <rostedt@goodmis.org>
>>> Cc: Ingo Molnar <mingo@redhat.com>
>>> Cc: Howard McLauchlan <hmclauchlan@fb.com>
>>> Cc: Josef Bacik <jbacik@fb.com>
>>> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>>> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
>>> Signed-off-by: Song Liu <songliubraving@fb.com>
>>> ---
>>> kernel/trace/trace_uprobe.c | 49 +++++++++++++++------------------------------
>>> 1 file changed, 16 insertions(+), 33 deletions(-)
>>> 
>>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>>> index 34fd0e0..d9ee522c 100644
>>> --- a/kernel/trace/trace_uprobe.c
>>> +++ b/kernel/trace/trace_uprobe.c
>>> @@ -55,7 +55,7 @@ struct trace_uprobe {
>>>        struct list_head                list;
>>>        struct trace_uprobe_filter      filter;
>>>        struct uprobe_consumer          consumer;
>>> -       struct inode                    *inode;
>>> +       struct path                     path;
>>>        char                            *filename;
>>>        unsigned long                   offset;
>>>        unsigned long                   nhit;
>>> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>>>        for (i = 0; i < tu->tp.nr_args; i++)
>>>                traceprobe_free_probe_arg(&tu->tp.args[i]);
>>> 
>>> -       iput(tu->inode);
>>> +       path_put(&tu->path);
>>>        kfree(tu->tp.call.class->system);
>>>        kfree(tu->tp.call.name);
>>>        kfree(tu->filename);
>>> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>>> static int create_trace_uprobe(int argc, char **argv)
>>> {
>>>        struct trace_uprobe *tu;
>>> -       struct inode *inode;
>>>        char *arg, *event, *group, *filename;
>>>        char buf[MAX_EVENT_NAME_LEN];
>>>        struct path path;
>>> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>>>        bool is_delete, is_return;
>>>        int i, ret;
>>> 
>>> -       inode = NULL;
>>>        ret = 0;
>>>        is_delete = false;
>>>        is_return = false;
>>> @@ -437,24 +435,14 @@ static int create_trace_uprobe(int argc, char **argv)
>>>        }
>>>        /* Find the last occurrence, in case the path contains ':' too. */
>>>        arg = strrchr(argv[1], ':');
>>> -       if (!arg) {
>>> -               ret = -EINVAL;
>>> -               goto fail_address_parse;
>>> -       }
>>> +       if (!arg)
>>> +               return -EINVAL;
>>> 
>>>        *arg++ = '\0';
>>>        filename = argv[1];
>>>        ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>>        if (ret)
>>> -               goto fail_address_parse;
>>> -
>>> -       inode = igrab(d_real_inode(path.dentry));
> 
> Also, where has the d_real_inode() gone?
> 
> Looks like we need tu->inode back, since the return value of
> d_real_inode() may change over time.   I'd do the "tu->inode =
> d_real_inode(tu->path.dentry)" just before first use (i.e. when
> enabling the tracepoint).
> 
> Thanks,
> Miklos
> 

Do we need mechanism to prevent the return value of d_real_inode()
to change? Would the following sequence happen?

    create trace_uprobe
    enable trace_uprobe (uprobe_register)
    d_real changes
    disable trace_uprobe (uprobe_unregister get wrong inode?)
 
Another case might be:

    create trace_uprobe
    enable trace_uprobe (uprobe_register)
    disable trace_uprobe (uprobe_unregister)
    d_real changes
    enable trace_uprobe (do we need new inode for uprobe_register)

Thanks,
Song

> 
>>> -       path_put(&path);
>>> -
>>> -       if (!inode || !S_ISREG(inode->i_mode)) {
>> 
>> Where has the S_ISREG check gone?
>> 
>>> -               ret = -EINVAL;
>>> -               goto fail_address_parse;
>>> -       }
>>> +               return ret;
>>> 
>>>        ret = kstrtoul(arg, 0, &offset);
>>>        if (ret)
>>> @@ -490,7 +478,7 @@ static int create_trace_uprobe(int argc, char **argv)
>>>                goto fail_address_parse;
>>>        }
>>>        tu->offset = offset;
>>> -       tu->inode = inode;
>>> +       tu->path = path;
>>>        tu->filename = kstrdup(filename, GFP_KERNEL);
>>> 
>>>        if (!tu->filename) {
>>> @@ -558,7 +546,7 @@ static int create_trace_uprobe(int argc, char **argv)
>>>        return ret;
>>> 
>>> fail_address_parse:
>>> -       iput(inode);
>>> +       path_put(&path);
>>> 
>>>        pr_info("Failed to parse address or file.\n");
>>> 
>>> @@ -922,7 +910,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>>>                goto err_flags;
>>> 
>>>        tu->consumer.filter = filter;
>>> -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>>> +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
>>> +                             &tu->consumer);
>>>        if (ret)
>>>                goto err_buffer;
>>> 
>>> @@ -966,7 +955,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>>> 
>>>        WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>>> 
>>> -       uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>>> +       uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>>>        tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>>> 
>>>        uprobe_buffer_disable();
>>> @@ -1041,7 +1030,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>>>        write_unlock(&tu->filter.rwlock);
>>> 
>>>        if (!done)
>>> -               return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
>>> +               return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
>>> +                                   &tu->consumer, false);
>>> 
>>>        return 0;
>>> }
>>> @@ -1073,7 +1063,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>>> 
>>>        err = 0;
>>>        if (!done) {
>>> -               err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
>>> +               err = uprobe_apply(d_inode(tu->path.dentry),
>>> +                                  tu->offset, &tu->consumer, true);
>>>                if (err)
>>>                        uprobe_perf_close(tu, event);
>>>        }
>>> @@ -1337,7 +1328,6 @@ struct trace_event_call *
>>> create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>>> {
>>>        struct trace_uprobe *tu;
>>> -       struct inode *inode;
>>>        struct path path;
>>>        int ret;
>>> 
>>> @@ -1345,14 +1335,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>>>        if (ret)
>>>                return ERR_PTR(ret);
>>> 
>>> -       inode = igrab(d_inode(path.dentry));
>>> -       path_put(&path);
>>> -
>>> -       if (!inode || !S_ISREG(inode->i_mode)) {
>> 
>> And here, again.
>> 
>> Otherwise ACK.
>> 
>> Also please create a separate patch that removes igrab/iput calls from
>> kernel/events/uprobes.c and adds a comment to the effect that the
>> caller is required to keep the inode (and the containing mount)
>> referenced.
>> 
>> Thanks,
>> Miklos

Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Miklos Szeredi]

On Thu, Apr 19, 2018 at 6:37 PM, Song Liu <songliubraving@fb.com> wrote:
>
>
>> On Apr 19, 2018, at 7:44 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>>
>> On Thu, Apr 19, 2018 at 10:58 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>>> On Wed, Apr 18, 2018 at 7:40 PM, Song Liu <songliubraving@fb.com> wrote:

>>>>        *arg++ = '\0';
>>>>        filename = argv[1];
>>>>        ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>>>        if (ret)
>>>> -               goto fail_address_parse;
>>>> -
>>>> -       inode = igrab(d_real_inode(path.dentry));
>>
>> Also, where has the d_real_inode() gone?
>>
>> Looks like we need tu->inode back, since the return value of
>> d_real_inode() may change over time.   I'd do the "tu->inode =
>> d_real_inode(tu->path.dentry)" just before first use (i.e. when
>> enabling the tracepoint).
>>

>
> Do we need mechanism to prevent the return value of d_real_inode()
> to change? Would the following sequence happen?
>
>     create trace_uprobe
>     enable trace_uprobe (uprobe_register)
>     d_real changes
>     disable trace_uprobe (uprobe_unregister get wrong inode?)

Yes.

>
> Another case might be:
>
>     create trace_uprobe
>     enable trace_uprobe (uprobe_register)
>     disable trace_uprobe (uprobe_unregister)
>     d_real changes
>     enable trace_uprobe (do we need new inode for uprobe_register)

Probably a good idea to use the new one, but doesn't really matter.
Do the one that's simpler.

This corner case is simply not interesting (modifying a binary while
it is being debugged with uprobe).  Let's just concentrate on making
this crash and leak free.

Thanks,
Miklos

Re: [PATCH v2] tracing: fix bad use of igrab in trace_uprobe.c

[Steven Rostedt]

On Fri, 20 Apr 2018 16:34:25 +0200
Miklos Szeredi <miklos@szeredi.hu> wrote:

> This corner case is simply not interesting (modifying a binary while
> it is being debugged with uprobe).  Let's just concentrate on making
> this crash and leak free.

Yes please. I'm waiting for a final patch to run my tests. I have other
patches that need to go mainline as well, and I'll start testing all of
them when I get the final version of this one.

-- Steve