LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: ebiederm@xmission.com (Eric W. Biederman)
To: Nathan Chancellor <nathan@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>,
	Alexey Gladkov <legion@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] ucounts: add missing data type changes
Date: Thu, 05 Aug 2021 11:48:43 -0500	[thread overview]
Message-ID: <87v94jalck.fsf@disp2133> (raw)
In-Reply-To: <94478003-8259-4b57-6d93-5a07e0750946@kernel.org> (Nathan Chancellor's message of "Wed, 4 Aug 2021 13:27:08 -0700")

Nathan Chancellor <nathan@kernel.org> writes:

> Hi Eric,
>
> On 8/4/2021 12:47 PM, Eric W. Biederman wrote:
>> Nathan Chancellor <nathan@kernel.org> writes:
>>
>>> On Fri, Jul 30, 2021 at 08:28:54AM +0200, Sven Schnelle wrote:
>>>> commit f9c82a4ea89c3 ("Increase size of ucounts to atomic_long_t")
>>>> changed the data type of ucounts/ucounts_max to long, but missed to
>>>> adjust a few other places. This is noticeable on big endian platforms
>>>> from user space because the /proc/sys/user/max_*_names files all
>>>> contain 0.
>>>>
>>>> Fixes: f9c82a4ea89c ("Increase size of ucounts to atomic_long_t")
>>>> Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
>>>
>>> This patch in -next as commit e43fc41d1f7f ("ucounts: add missing data type
>>> changes") causes Windows Subsystem for Linux to fail to start:
>>>
>>> [error 0x8007010b when launching `wsl.exe -d Arch'] Could not access starting
>>> directory "\\wsl$\Arch\home\nathan"
>>>
>>> Specifically, it is the change to max_user_watches in
>>> fs/notify/inotify/inotify_user.c, as the below diff gets me back to working.
>>> Unfortunately, I have no additional information to offer beyond that as WSL's
>>> init is custom and closed source (as far as I am aware) and there are no real
>>> debugging utilities.
>>
>> Could you try this patch and tell us what value is being set?
>>
>> The only think I can imagine is that someone wants unlimited watches and
>> sets the value to a ridiculously large value and the interpretation of
>> that value winds up being different between int and long.
>>
>> This should allow you to read either dmesg or the kernel's log as it
>> boots up and see what value is being written.  From there it should
>> be relatively straight forward to figure out what is going on.
>
> I applied this diff on top of mine and running 'dmesg |& grep intvec' shows:
>
> [    0.282500] intvec: dmesg_restrict <- 0
> [    0.282510] intvec: max_user_watches <- 524288
>
> This seems much smaller than INT_MAX so I am not sure how the value could be
> different between int and long but I am not at all familiar with the sysctl
> code.
>
> More than happy to continue to test debug patches or provide any additional
> information as I can.

Yes.  Very strange.

Could you perhaps try the instrumenting proc_doulongvec_minmax the same
way and see what is written in the failing case?

While looking at the code I did see one other serious bug.  The min and
max values are int constants intstead of long constants.

Could you test the change below and see if it makes a difference?

Eric


diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 6576657a1a25..28b67cb9458d 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -54,6 +54,9 @@ static int fanotify_max_queued_events __read_mostly;
 
 #include <linux/sysctl.h>
 
+static long ft_zero = 0;
+static long ft_int_max = INT_MAX;
+
 struct ctl_table fanotify_table[] = {
 	{
 		.procname	= "max_user_groups",
@@ -61,8 +64,8 @@ struct ctl_table fanotify_table[] = {
 		.maxlen		= sizeof(long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_INT_MAX,
+		.extra1		= &ft_zero,
+		.extra2		= &ft_int_max,
 	},
 	{
 		.procname	= "max_user_marks",
@@ -70,8 +73,8 @@ struct ctl_table fanotify_table[] = {
 		.maxlen		= sizeof(long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_INT_MAX,
+		.extra1		= &ft_zero,
+		.extra2		= &ft_int_max,
 	},
 	{
 		.procname	= "max_queued_events",
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index 55fe7cdea2fb..62051247f6d2 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -55,6 +55,9 @@ struct kmem_cache *inotify_inode_mark_cachep __read_mostly;
 
 #include <linux/sysctl.h>
 
+static long it_zero = 0;
+static long it_int_max = INT_MAX;
+
 struct ctl_table inotify_table[] = {
 	{
 		.procname	= "max_user_instances",
@@ -62,8 +65,8 @@ struct ctl_table inotify_table[] = {
 		.maxlen		= sizeof(long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_INT_MAX,
+		.extra1		= &it_zero,
+		.extra2		= &it_int_max,
 	},
 	{
 		.procname	= "max_user_watches",
@@ -71,8 +74,8 @@ struct ctl_table inotify_table[] = {
 		.maxlen		= sizeof(long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_INT_MAX,
+		.extra1		= &it_zero,
+		.extra2		= &it_int_max,
 	},
 	{
 		.procname	= "max_queued_events",
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 260ae7da815f..bb51849e6375 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -58,14 +58,17 @@ static struct ctl_table_root set_root = {
 	.permissions = set_permissions,
 };
 
+static long ue_zero = 0;
+static long ue_int_max = INT_MAX;
+
 #define UCOUNT_ENTRY(name)					\
 	{							\
 		.procname	= name,				\
 		.maxlen		= sizeof(long),			\
 		.mode		= 0644,				\
 		.proc_handler	= proc_doulongvec_minmax,	\
-		.extra1		= SYSCTL_ZERO,			\
-		.extra2		= SYSCTL_INT_MAX,		\
+		.extra1		= &ue_zero,			\
+		.extra2		= &ue_int_max,			\
 	}
 static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_user_namespaces"),




  reply	other threads:[~2021-08-05 16:49 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30  6:28 Sven Schnelle
2021-07-30 17:52 ` Eric W. Biederman
2021-08-04  2:40 ` Nathan Chancellor
2021-08-04 19:47   ` Eric W. Biederman
2021-08-04 20:27     ` Nathan Chancellor
2021-08-05 16:48       ` Eric W. Biederman [this message]
2021-08-05 19:26         ` Nathan Chancellor
2021-08-06 10:36           ` Naresh Kamboju
2021-08-09 20:43             ` [PATCH v4] " Eric W. Biederman
2021-08-10  9:01               ` Jan Kara

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87v94jalck.fsf@disp2133 \
    --to=ebiederm@xmission.com \
    --cc=legion@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=nathan@kernel.org \
    --cc=svens@linux.ibm.com \
    --subject='Re: [PATCH v3] ucounts: add missing data type changes' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).