[PATCH v2 0/2] proc: Relax check of mount visibility

[PATCH v2 0/2] proc: Relax check of mount visibility

[Alexey Gladkov]

If only the dynamic part of procfs is mounted (subset=pid), then there is no
need to check if procfs is fully visible to the user in the new user namespace.

Alexey Gladkov (2):
  proc: Relax check of mount visibility
  Show /proc/self/net only for CAP_NET_ADMIN

 fs/namespace.c          | 27 ++++++++++++++++-----------
 fs/proc/proc_net.c      |  8 ++++++++
 fs/proc/root.c          | 21 +++++++++++++++------
 include/linux/fs.h      |  1 +
 include/linux/proc_fs.h |  1 +
 5 files changed, 41 insertions(+), 17 deletions(-)

-- 
2.25.4

[PATCH v2 1/2] proc: Relax check of mount visibility

[Alexey Gladkov]

Allow to mount of procfs with subset=pid option even if the entire
procfs is not fully accessible to the user.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 fs/namespace.c     | 27 ++++++++++++++++-----------
 fs/proc/root.c     | 16 +++++++++-------
 include/linux/fs.h |  1 +
 3 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 4a0f600a3328..ab9d607921da 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3949,18 +3949,23 @@ static bool mnt_already_visible(struct mnt_namespace *ns,
 		    ((mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
 			continue;
 
-		/* This mount is not fully visible if there are any
-		 * locked child mounts that cover anything except for
-		 * empty directories.
+		/* If this filesystem is completely dynamic, then it
+		 * makes no sense to check for any child mounts.
 		 */
-		list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
-			struct inode *inode = child->mnt_mountpoint->d_inode;
-			/* Only worry about locked mounts */
-			if (!(child->mnt.mnt_flags & MNT_LOCKED))
-				continue;
-			/* Is the directory permanetly empty? */
-			if (!is_empty_dir_inode(inode))
-				goto next;
+		if (!(sb->s_iflags & SB_I_DYNAMIC)) {
+			/* This mount is not fully visible if there are any
+			 * locked child mounts that cover anything except for
+			 * empty directories.
+			 */
+			list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
+				struct inode *inode = child->mnt_mountpoint->d_inode;
+				/* Only worry about locked mounts */
+				if (!(child->mnt.mnt_flags & MNT_LOCKED))
+					continue;
+				/* Is the directory permanetly empty? */
+				if (!is_empty_dir_inode(inode))
+					goto next;
+			}
 		}
 		/* Preserve the locked attributes */
 		*new_mnt_flags |= mnt_flags & (MNT_LOCK_READONLY | \
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 5e444d4f9717..c6bf74de1906 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -145,18 +145,21 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 	return 0;
 }
 
-static void proc_apply_options(struct proc_fs_info *fs_info,
+static void proc_apply_options(struct super_block *s,
 			       struct fs_context *fc,
 			       struct user_namespace *user_ns)
 {
 	struct proc_fs_context *ctx = fc->fs_private;
+	struct proc_fs_info *fs_info = proc_sb_info(s);
 
 	if (ctx->mask & (1 << Opt_gid))
 		fs_info->pid_gid = make_kgid(user_ns, ctx->gid);
 	if (ctx->mask & (1 << Opt_hidepid))
 		fs_info->hide_pid = ctx->hidepid;
-	if (ctx->mask & (1 << Opt_subset))
+	if (ctx->mask & (1 << Opt_subset)) {
 		fs_info->pidonly = ctx->pidonly;
+		s->s_iflags |= SB_I_DYNAMIC;
+	}
 }
 
 static int proc_fill_super(struct super_block *s, struct fs_context *fc)
@@ -170,9 +173,6 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	if (!fs_info)
 		return -ENOMEM;
 
-	fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
-	proc_apply_options(fs_info, fc, current_user_ns());
-
 	/* User space would break if executables or devices appear on proc */
 	s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
 	s->s_flags |= SB_NODIRATIME | SB_NOSUID | SB_NOEXEC;
@@ -183,6 +183,9 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_time_gran = 1;
 	s->s_fs_info = fs_info;
 
+	fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
+	proc_apply_options(s, fc, current_user_ns());
+
 	/*
 	 * procfs isn't actually a stacking filesystem; however, there is
 	 * too much magic going on inside it to permit stacking things on
@@ -216,11 +219,10 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 static int proc_reconfigure(struct fs_context *fc)
 {
 	struct super_block *sb = fc->root->d_sb;
-	struct proc_fs_info *fs_info = proc_sb_info(sb);
 
 	sync_filesystem(sb);
 
-	proc_apply_options(fs_info, fc, current_user_ns());
+	proc_apply_options(sb, fc, current_user_ns());
 	return 0;
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f5abba86107d..aff5ed9e8f82 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1413,6 +1413,7 @@ extern int send_sigurg(struct fown_struct *fown);
 #define SB_I_USERNS_VISIBLE		0x00000010 /* fstype already mounted */
 #define SB_I_IMA_UNVERIFIABLE_SIGNATURE	0x00000020
 #define SB_I_UNTRUSTED_MOUNTER		0x00000040
+#define SB_I_DYNAMIC			0x00000080
 
 #define SB_I_SKIP_SYNC	0x00000100	/* Skip superblock at global sync */
 
-- 
2.25.4

[PATCH v2 2/2] Show /proc/self/net only for CAP_NET_ADMIN

[Alexey Gladkov]

Cache the mounters credentials and make access to the net directories
contingent of the permissions of the mounter of proc.

Show /proc/self/net only if mounter has CAP_NET_ADMIN and if proc is
mounted with subset=pid option.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 fs/proc/proc_net.c      | 8 ++++++++
 fs/proc/root.c          | 7 +++++++
 include/linux/proc_fs.h | 1 +
 3 files changed, 16 insertions(+)

diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index dba63b2429f0..c43fc5c907db 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -26,6 +26,7 @@
 #include <linux/uidgid.h>
 #include <net/net_namespace.h>
 #include <linux/seq_file.h>
+#include <linux/security.h>
 
 #include "internal.h"
 
@@ -275,6 +276,7 @@ static struct net *get_proc_task_net(struct inode *dir)
 	struct task_struct *task;
 	struct nsproxy *ns;
 	struct net *net = NULL;
+	struct proc_fs_info *fs_info = proc_sb_info(dir->i_sb);
 
 	rcu_read_lock();
 	task = pid_task(proc_pid(dir), PIDTYPE_PID);
@@ -287,6 +289,12 @@ static struct net *get_proc_task_net(struct inode *dir)
 	}
 	rcu_read_unlock();
 
+	if (net && (fs_info->pidonly == PROC_PIDONLY_ON) &&
+	    security_capable(fs_info->mounter_cred, net->user_ns, CAP_NET_ADMIN, CAP_OPT_NONE) < 0) {
+		put_net(net);
+		net = NULL;
+	}
+
 	return net;
 }
 
diff --git a/fs/proc/root.c b/fs/proc/root.c
index c6bf74de1906..eeeda375cf85 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -184,6 +184,8 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_fs_info = fs_info;
 
 	fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
+	fs_info->mounter_cred = get_cred(fc->cred);
+
 	proc_apply_options(s, fc, current_user_ns());
 
 	/*
@@ -219,9 +221,13 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 static int proc_reconfigure(struct fs_context *fc)
 {
 	struct super_block *sb = fc->root->d_sb;
+	struct proc_fs_info *fs_info = proc_sb_info(sb);
 
 	sync_filesystem(sb);
 
+	put_cred(fs_info->mounter_cred);
+	fs_info->mounter_cred = get_cred(fc->cred);
+
 	proc_apply_options(sb, fc, current_user_ns());
 	return 0;
 }
@@ -276,6 +282,7 @@ static void proc_kill_sb(struct super_block *sb)
 
 	kill_anon_super(sb);
 	put_pid_ns(fs_info->pid_ns);
+	put_cred(fs_info->mounter_cred);
 	kfree(fs_info);
 }
 
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index d1eed1b43651..671c6dafc4ee 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -63,6 +63,7 @@ struct proc_fs_info {
 	kgid_t pid_gid;
 	enum proc_hidepid hide_pid;
 	enum proc_pidonly pidonly;
+	struct cred *mounter_cred;
 };
 
 static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)
-- 
2.25.4

Re: [PATCH v2 2/2] Show /proc/self/net only for CAP_NET_ADMIN

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 3986 bytes --]

Hi Alexey,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linux/master]
[also build test WARNING on kees/for-next/pstore linus/master v5.9-rc1 next-20200819]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Alexey-Gladkov/proc-Relax-check-of-mount-visibility/20200820-031542
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git bcf876870b95592b52519ed4aafcf9d95999bc9c
config: xtensa-allyesconfig (attached as .config)
compiler: xtensa-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=xtensa 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   fs/proc/root.c: In function 'proc_fill_super':
>> fs/proc/root.c:187:24: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
     187 |  fs_info->mounter_cred = get_cred(fc->cred);
         |                        ^
   fs/proc/root.c: In function 'proc_reconfigure':
   fs/proc/root.c:229:24: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
     229 |  fs_info->mounter_cred = get_cred(fc->cred);
         |                        ^

# https://github.com/0day-ci/linux/commit/9c2a0eea7f38b1a4e201b8f2da0c5fd7b423daf9
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Alexey-Gladkov/proc-Relax-check-of-mount-visibility/20200820-031542
git checkout 9c2a0eea7f38b1a4e201b8f2da0c5fd7b423daf9
vim +/const +187 fs/proc/root.c

   164	
   165	static int proc_fill_super(struct super_block *s, struct fs_context *fc)
   166	{
   167		struct proc_fs_context *ctx = fc->fs_private;
   168		struct inode *root_inode;
   169		struct proc_fs_info *fs_info;
   170		int ret;
   171	
   172		fs_info = kzalloc(sizeof(*fs_info), GFP_KERNEL);
   173		if (!fs_info)
   174			return -ENOMEM;
   175	
   176		/* User space would break if executables or devices appear on proc */
   177		s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
   178		s->s_flags |= SB_NODIRATIME | SB_NOSUID | SB_NOEXEC;
   179		s->s_blocksize = 1024;
   180		s->s_blocksize_bits = 10;
   181		s->s_magic = PROC_SUPER_MAGIC;
   182		s->s_op = &proc_sops;
   183		s->s_time_gran = 1;
   184		s->s_fs_info = fs_info;
   185	
   186		fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
 > 187		fs_info->mounter_cred = get_cred(fc->cred);
   188	
   189		proc_apply_options(s, fc, current_user_ns());
   190	
   191		/*
   192		 * procfs isn't actually a stacking filesystem; however, there is
   193		 * too much magic going on inside it to permit stacking things on
   194		 * top of it
   195		 */
   196		s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
   197	
   198		/* procfs dentries and inodes don't require IO to create */
   199		s->s_shrink.seeks = 0;
   200	
   201		pde_get(&proc_root);
   202		root_inode = proc_get_inode(s, &proc_root);
   203		if (!root_inode) {
   204			pr_err("proc_fill_super: get root inode failed\n");
   205			return -ENOMEM;
   206		}
   207	
   208		s->s_root = d_make_root(root_inode);
   209		if (!s->s_root) {
   210			pr_err("proc_fill_super: allocate dentry failed\n");
   211			return -ENOMEM;
   212		}
   213	
   214		ret = proc_setup_self(s);
   215		if (ret) {
   216			return ret;
   217		}
   218		return proc_setup_thread_self(s);
   219	}
   220	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
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Re: [PATCH v2 2/2] Show /proc/self/net only for CAP_NET_ADMIN

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 4177 bytes --]

Hi Alexey,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linux/master]
[also build test WARNING on kees/for-next/pstore linus/master v5.9-rc1 next-20200819]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Alexey-Gladkov/proc-Relax-check-of-mount-visibility/20200820-031542
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git bcf876870b95592b52519ed4aafcf9d95999bc9c
config: m68k-randconfig-s032-20200819 (attached as .config)
compiler: m68k-linux-gcc (GCC) 9.3.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.2-183-gaa6ede3b-dirty
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=m68k 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)

>> fs/proc/root.c:187:31: sparse: sparse: incorrect type in assignment (different modifiers) @@     expected struct cred *mounter_cred @@     got struct cred const * @@
>> fs/proc/root.c:187:31: sparse:     expected struct cred *mounter_cred
>> fs/proc/root.c:187:31: sparse:     got struct cred const *
   fs/proc/root.c:229:31: sparse: sparse: incorrect type in assignment (different modifiers) @@     expected struct cred *mounter_cred @@     got struct cred const * @@
   fs/proc/root.c:229:31: sparse:     expected struct cred *mounter_cred
   fs/proc/root.c:229:31: sparse:     got struct cred const *

# https://github.com/0day-ci/linux/commit/9c2a0eea7f38b1a4e201b8f2da0c5fd7b423daf9
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Alexey-Gladkov/proc-Relax-check-of-mount-visibility/20200820-031542
git checkout 9c2a0eea7f38b1a4e201b8f2da0c5fd7b423daf9
vim +187 fs/proc/root.c

   164	
   165	static int proc_fill_super(struct super_block *s, struct fs_context *fc)
   166	{
   167		struct proc_fs_context *ctx = fc->fs_private;
   168		struct inode *root_inode;
   169		struct proc_fs_info *fs_info;
   170		int ret;
   171	
   172		fs_info = kzalloc(sizeof(*fs_info), GFP_KERNEL);
   173		if (!fs_info)
   174			return -ENOMEM;
   175	
   176		/* User space would break if executables or devices appear on proc */
   177		s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
   178		s->s_flags |= SB_NODIRATIME | SB_NOSUID | SB_NOEXEC;
   179		s->s_blocksize = 1024;
   180		s->s_blocksize_bits = 10;
   181		s->s_magic = PROC_SUPER_MAGIC;
   182		s->s_op = &proc_sops;
   183		s->s_time_gran = 1;
   184		s->s_fs_info = fs_info;
   185	
   186		fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
 > 187		fs_info->mounter_cred = get_cred(fc->cred);
   188	
   189		proc_apply_options(s, fc, current_user_ns());
   190	
   191		/*
   192		 * procfs isn't actually a stacking filesystem; however, there is
   193		 * too much magic going on inside it to permit stacking things on
   194		 * top of it
   195		 */
   196		s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
   197	
   198		/* procfs dentries and inodes don't require IO to create */
   199		s->s_shrink.seeks = 0;
   200	
   201		pde_get(&proc_root);
   202		root_inode = proc_get_inode(s, &proc_root);
   203		if (!root_inode) {
   204			pr_err("proc_fill_super: get root inode failed\n");
   205			return -ENOMEM;
   206		}
   207	
   208		s->s_root = d_make_root(root_inode);
   209		if (!s->s_root) {
   210			pr_err("proc_fill_super: allocate dentry failed\n");
   211			return -ENOMEM;
   212		}
   213	
   214		ret = proc_setup_self(s);
   215		if (ret) {
   216			return ret;
   217		}
   218		return proc_setup_thread_self(s);
   219	}
   220	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 23980 bytes --]

Re: [PATCH v2 2/2] Show /proc/self/net only for CAP_NET_ADMIN

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 4201 bytes --]

Hi Alexey,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linux/master]
[also build test ERROR on kees/for-next/pstore linus/master v5.9-rc1 next-20200819]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Alexey-Gladkov/proc-Relax-check-of-mount-visibility/20200820-031542
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git bcf876870b95592b52519ed4aafcf9d95999bc9c
config: s390-randconfig-r034-20200818 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project b34b1e38381fa4d1b1d9751a6b5233b68e734cfe)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install s390 cross compiling tool for clang build
        # apt-get install binutils-s390x-linux-gnu
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=s390 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> fs/proc/root.c:187:24: error: assigning to 'struct cred *' from 'const struct cred *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
           fs_info->mounter_cred = get_cred(fc->cred);
                                 ^ ~~~~~~~~~~~~~~~~~~
   fs/proc/root.c:229:24: error: assigning to 'struct cred *' from 'const struct cred *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
           fs_info->mounter_cred = get_cred(fc->cred);
                                 ^ ~~~~~~~~~~~~~~~~~~
   2 errors generated.

# https://github.com/0day-ci/linux/commit/9c2a0eea7f38b1a4e201b8f2da0c5fd7b423daf9
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Alexey-Gladkov/proc-Relax-check-of-mount-visibility/20200820-031542
git checkout 9c2a0eea7f38b1a4e201b8f2da0c5fd7b423daf9
vim +187 fs/proc/root.c

   164	
   165	static int proc_fill_super(struct super_block *s, struct fs_context *fc)
   166	{
   167		struct proc_fs_context *ctx = fc->fs_private;
   168		struct inode *root_inode;
   169		struct proc_fs_info *fs_info;
   170		int ret;
   171	
   172		fs_info = kzalloc(sizeof(*fs_info), GFP_KERNEL);
   173		if (!fs_info)
   174			return -ENOMEM;
   175	
   176		/* User space would break if executables or devices appear on proc */
   177		s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
   178		s->s_flags |= SB_NODIRATIME | SB_NOSUID | SB_NOEXEC;
   179		s->s_blocksize = 1024;
   180		s->s_blocksize_bits = 10;
   181		s->s_magic = PROC_SUPER_MAGIC;
   182		s->s_op = &proc_sops;
   183		s->s_time_gran = 1;
   184		s->s_fs_info = fs_info;
   185	
   186		fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
 > 187		fs_info->mounter_cred = get_cred(fc->cred);
   188	
   189		proc_apply_options(s, fc, current_user_ns());
   190	
   191		/*
   192		 * procfs isn't actually a stacking filesystem; however, there is
   193		 * too much magic going on inside it to permit stacking things on
   194		 * top of it
   195		 */
   196		s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
   197	
   198		/* procfs dentries and inodes don't require IO to create */
   199		s->s_shrink.seeks = 0;
   200	
   201		pde_get(&proc_root);
   202		root_inode = proc_get_inode(s, &proc_root);
   203		if (!root_inode) {
   204			pr_err("proc_fill_super: get root inode failed\n");
   205			return -ENOMEM;
   206		}
   207	
   208		s->s_root = d_make_root(root_inode);
   209		if (!s->s_root) {
   210			pr_err("proc_fill_super: allocate dentry failed\n");
   211			return -ENOMEM;
   212		}
   213	
   214		ret = proc_setup_self(s);
   215		if (ret) {
   216			return ret;
   217		}
   218		return proc_setup_thread_self(s);
   219	}
   220	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 29945 bytes --]

[PATCH v2 2/2] Show /proc/self/net only for CAP_NET_ADMIN

[Alexey Gladkov]

Cache the mounters credentials and make access to the net directories
contingent of the permissions of the mounter of proc.

Show /proc/self/net only if mounter has CAP_NET_ADMIN and if proc is
mounted with subset=pid option.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
 fs/proc/proc_net.c      | 8 ++++++++
 fs/proc/root.c          | 7 +++++++
 include/linux/proc_fs.h | 1 +
 3 files changed, 16 insertions(+)

diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index dba63b2429f0..c43fc5c907db 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -26,6 +26,7 @@
 #include <linux/uidgid.h>
 #include <net/net_namespace.h>
 #include <linux/seq_file.h>
+#include <linux/security.h>
 
 #include "internal.h"
 
@@ -275,6 +276,7 @@ static struct net *get_proc_task_net(struct inode *dir)
 	struct task_struct *task;
 	struct nsproxy *ns;
 	struct net *net = NULL;
+	struct proc_fs_info *fs_info = proc_sb_info(dir->i_sb);
 
 	rcu_read_lock();
 	task = pid_task(proc_pid(dir), PIDTYPE_PID);
@@ -287,6 +289,12 @@ static struct net *get_proc_task_net(struct inode *dir)
 	}
 	rcu_read_unlock();
 
+	if (net && (fs_info->pidonly == PROC_PIDONLY_ON) &&
+	    security_capable(fs_info->mounter_cred, net->user_ns, CAP_NET_ADMIN, CAP_OPT_NONE) < 0) {
+		put_net(net);
+		net = NULL;
+	}
+
 	return net;
 }
 
diff --git a/fs/proc/root.c b/fs/proc/root.c
index c6bf74de1906..eeeda375cf85 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -184,6 +184,8 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_fs_info = fs_info;
 
 	fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
+	fs_info->mounter_cred = get_cred(fc->cred);
+
 	proc_apply_options(s, fc, current_user_ns());
 
 	/*
@@ -219,9 +221,13 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 static int proc_reconfigure(struct fs_context *fc)
 {
 	struct super_block *sb = fc->root->d_sb;
+	struct proc_fs_info *fs_info = proc_sb_info(sb);
 
 	sync_filesystem(sb);
 
+	put_cred(fs_info->mounter_cred);
+	fs_info->mounter_cred = get_cred(fc->cred);
+
 	proc_apply_options(sb, fc, current_user_ns());
 	return 0;
 }
@@ -276,6 +282,7 @@ static void proc_kill_sb(struct super_block *sb)
 
 	kill_anon_super(sb);
 	put_pid_ns(fs_info->pid_ns);
+	put_cred(fs_info->mounter_cred);
 	kfree(fs_info);
 }
 
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index d1eed1b43651..671c6dafc4ee 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -63,6 +63,7 @@ struct proc_fs_info {
 	kgid_t pid_gid;
 	enum proc_hidepid hide_pid;
 	enum proc_pidonly pidonly;
+	struct cred *mounter_cred;
 };
 
 static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)
-- 
2.25.4