[PATCH] proc: align mnt_id in /proc/pid/fdinfo and /proc/pid/mountinfo

[PATCH] proc: align mnt_id in /proc/pid/fdinfo and /proc/pid/mountinfo

[Chen, Hu]

For Android application process, we found that the mnt_id read from
/proc/pid/fdinfo doesn't exist in /proc/pid/mountinfo. Thus CRIU fails
to dump such process and it complains

"(00.019206) Error (criu/files-reg.c:1299): Can't lookup mount=42 for
fd=-3 path=/data/dalvik-cache/x86_64/system@framework@boot.art"

This is due to how Android application is launched. In Android, there is
a special process called Zygote which handles the forking of each new
application process:
0. Zygote opens and maps some files, for example
   "/data/dalvik-cache/x86_64/system@framework@boot.art" in its current
   mount namespace, say "old mnt ns".
1. Zygote waits for the request to fork a new application.
2. Zygote gets a request, it forks and run the new process in a new
   mount namespace, say "new mnt ns".

The file opened in step 0 ties to the mount point in "old mnt ns". The
mnt_id of that mount is listed in /proc/pid/fdinfo. However,
/proc/pid/mountinfo points to current ns, i.e., "new mnt ns".

Althgouh this issue is exposed in Android, we believe it's generic.
Prcoess may open files and enter new mnt ns.

To address it, this patch searches the mirror mount in current ns with
MAJOR and MINOR and shows the mirror's mnt_id.

Signed-off-by: Chen, Hu <hu1.chen@intel.com>

diff --git a/fs/mount.h b/fs/mount.h
index 711a4093e475..6bbfc2b3b8ba 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -153,3 +153,5 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
 {
 	return ns->seq == 0;
 }
+
+extern struct mount *lookup_mirror_mnt(const struct mount *mnt);
diff --git a/fs/namespace.c b/fs/namespace.c
index 2adfe7b166a3..4ea9b4464cd0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -683,6 +683,36 @@ bool __is_local_mountpoint(struct dentry *dentry)
 	return is_covered;
 }
 
+/*
+ * lookup_mirror_mnt - Return @mnt's mirror mount in the current/local mount
+ * namespace. If mirror isn't found, just return NULL.
+ */
+struct mount *lookup_mirror_mnt(const struct mount *mnt)
+{
+	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
+	struct mount *mnt_local;
+	bool is_matched = false;
+
+	/* mnt belongs to current namesapce */
+	if (mnt->mnt_ns == ns)
+		return mnt;
+
+	down_read(&namespace_sem);
+	list_for_each_entry(mnt_local, &ns->list, mnt_list) {
+		struct super_block *sb = mnt->mnt.mnt_sb;
+		struct super_block *sb_local = mnt_local->mnt.mnt_sb;
+
+		if (MAJOR(sb->s_dev) == MAJOR(sb_local->s_dev) &&
+		    MINOR(sb->s_dev) == MINOR(sb_local->s_dev)) {
+			is_matched = true;
+			break;
+		}
+	}
+	up_read(&namespace_sem);
+
+	return is_matched ? mnt_local : NULL;
+}
+
 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
 {
 	struct hlist_head *chain = mp_hash(dentry);
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 81882a13212d..cbf2571b0620 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -23,6 +23,7 @@ static int seq_show(struct seq_file *m, void *v)
 	int f_flags = 0, ret = -ENOENT;
 	struct file *file = NULL;
 	struct task_struct *task;
+	struct mount *mount = NULL;
 
 	task = get_proc_task(m->private);
 	if (!task)
@@ -53,9 +54,16 @@ static int seq_show(struct seq_file *m, void *v)
 	if (ret)
 		return ret;
 
+	/* After unshare -m, real_mount(file->f_path.mnt) is not meaningful in
+	 * current mount namesapce. We want to know the mnt_id in current mount
+	 * namespace
+	 */
+	mount = lookup_mirror_mnt(real_mount(file->f_path.mnt));
+	if (!mount)
+		mount = real_mount(file->f_path.mnt);
+
 	seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
-		   (long long)file->f_pos, f_flags,
-		   real_mount(file->f_path.mnt)->mnt_id);
+		   (long long)file->f_pos, f_flags, mount->mnt_id);
 
 	show_fd_locks(m, file, files);
 	if (seq_has_overflowed(m))
-- 
2.22.0

Re: [PATCH] proc: align mnt_id in /proc/pid/fdinfo and /proc/pid/mountinfo

[Miklos Szeredi]

On Thu, Nov 21, 2019 at 8:28 AM Chen, Hu <hu1.chen@intel.com> wrote:
>
> For Android application process, we found that the mnt_id read from
> /proc/pid/fdinfo doesn't exist in /proc/pid/mountinfo. Thus CRIU fails
> to dump such process and it complains
>
> "(00.019206) Error (criu/files-reg.c:1299): Can't lookup mount=42 for
> fd=-3 path=/data/dalvik-cache/x86_64/system@framework@boot.art"
>
> This is due to how Android application is launched. In Android, there is
> a special process called Zygote which handles the forking of each new
> application process:
> 0. Zygote opens and maps some files, for example
>    "/data/dalvik-cache/x86_64/system@framework@boot.art" in its current
>    mount namespace, say "old mnt ns".
> 1. Zygote waits for the request to fork a new application.
> 2. Zygote gets a request, it forks and run the new process in a new
>    mount namespace, say "new mnt ns".
>
> The file opened in step 0 ties to the mount point in "old mnt ns". The
> mnt_id of that mount is listed in /proc/pid/fdinfo. However,
> /proc/pid/mountinfo points to current ns, i.e., "new mnt ns".
>
> Althgouh this issue is exposed in Android, we believe it's generic.
> Prcoess may open files and enter new mnt ns.
>
> To address it, this patch searches the mirror mount in current ns with
> MAJOR and MINOR and shows the mirror's mnt_id.

This is a hack.   I suggest instead to add a new line to fdinfo with
the MAJOR:MINOR number of the device.

Thanks,
Miklos

Re: [PATCH] proc: align mnt_id in /proc/pid/fdinfo and /proc/pid/mountinfo

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 2532 bytes --]

Hi Hu",

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v5.4-rc8 next-20191121]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Chen-Hu/proc-align-mnt_id-in-proc-pid-fdinfo-and-proc-pid-mountinfo/20191122-093927
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 81429eb8d9ca40b0c65bb739d29fa856c5d5e958
config: parisc-c3000_defconfig (attached as .config)
compiler: hppa-linux-gcc (GCC) 7.4.0
reproduce:
        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
        GCC_VERSION=7.4.0 make.cross ARCH=parisc 

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

All warnings (new ones prefixed by >>):

   fs/namespace.c: In function 'lookup_mirror_mnt':
>> fs/namespace.c:698:10: warning: return discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
      return mnt;
             ^~~

vim +/const +698 fs/namespace.c

   685	
   686	/*
   687	 * lookup_mirror_mnt - Return @mnt's mirror mount in the current/local mount
   688	 * namespace. If mirror isn't found, just return NULL.
   689	 */
   690	struct mount *lookup_mirror_mnt(const struct mount *mnt)
   691	{
   692		struct mnt_namespace *ns = current->nsproxy->mnt_ns;
   693		struct mount *mnt_local;
   694		bool is_matched = false;
   695	
   696		/* mnt belongs to current namesapce */
   697		if (mnt->mnt_ns == ns)
 > 698			return mnt;
   699	
   700		down_read(&namespace_sem);
   701		list_for_each_entry(mnt_local, &ns->list, mnt_list) {
   702			struct super_block *sb = mnt->mnt.mnt_sb;
   703			struct super_block *sb_local = mnt_local->mnt.mnt_sb;
   704	
   705			if (MAJOR(sb->s_dev) == MAJOR(sb_local->s_dev) &&
   706			    MINOR(sb->s_dev) == MINOR(sb_local->s_dev)) {
   707				is_matched = true;
   708				break;
   709			}
   710		}
   711		up_read(&namespace_sem);
   712	
   713		return is_matched ? mnt_local : NULL;
   714	}
   715	

---
0-DAY kernel test infrastructure                 Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation

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Re: [PATCH] proc: align mnt_id in /proc/pid/fdinfo and /proc/pid/mountinfo

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 2601 bytes --]

Hi Hu",

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v5.4-rc8 next-20191121]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Chen-Hu/proc-align-mnt_id-in-proc-pid-fdinfo-and-proc-pid-mountinfo/20191122-093927
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 81429eb8d9ca40b0c65bb739d29fa856c5d5e958
config: parisc-c3000_defconfig (attached as .config)
compiler: hppa-linux-gcc (GCC) 7.4.0
reproduce:
        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
        GCC_VERSION=7.4.0 make.cross ARCH=parisc 

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

All warnings (new ones prefixed by >>):

   fs/namespace.c: In function 'lookup_mirror_mnt':
>> fs/namespace.c:698:10: warning: return discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
      return mnt;
             ^~~

vim +/const +698 fs/namespace.c

   685	
   686	/*
   687	 * lookup_mirror_mnt - Return @mnt's mirror mount in the current/local mount
   688	 * namespace. If mirror isn't found, just return NULL.
   689	 */
   690	struct mount *lookup_mirror_mnt(const struct mount *mnt)
   691	{
   692		struct mnt_namespace *ns = current->nsproxy->mnt_ns;
   693		struct mount *mnt_local;
   694		bool is_matched = false;
   695	
   696		/* mnt belongs to current namesapce */
   697		if (mnt->mnt_ns == ns)
 > 698			return mnt;
   699	
   700		down_read(&namespace_sem);
   701		list_for_each_entry(mnt_local, &ns->list, mnt_list) {
   702			struct super_block *sb = mnt->mnt.mnt_sb;
   703			struct super_block *sb_local = mnt_local->mnt.mnt_sb;
   704	
   705			if (MAJOR(sb->s_dev) == MAJOR(sb_local->s_dev) &&
   706			    MINOR(sb->s_dev) == MINOR(sb_local->s_dev)) {
   707				is_matched = true;
   708				break;
   709			}
   710		}
   711		up_read(&namespace_sem);
   712	
   713		return is_matched ? mnt_local : NULL;
   714	}
   715	

---
0-DAY kernel test infrastructure                 Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org Intel Corporation

[-- Attachment #2: config.gz --]
[-- Type: application/gzip, Size: 15671 bytes --]

[PATCH v2] proc: align mnt_id in /proc/pid/fdinfo and /proc/pid/mountinfo

[Chen, Hu]

For Android application process, we found that the mnt_id read from
/proc/pid/fdinfo doesn't exist in /proc/pid/mountinfo. Thus CRIU fails
to dump such process and it complains

"(00.019206) Error (criu/files-reg.c:1299): Can't lookup mount=42 for
fd=-3 path=/data/dalvik-cache/x86_64/system@framework@boot.art"

This is due to how Android application is launched. In Android, there is
a special process called Zygote which handles the forking of each new
application process:
0. Zygote opens and maps some files, for example
   "/data/dalvik-cache/x86_64/system@framework@boot.art" in its current
   mount namespace, say "old mnt ns".
1. Zygote waits for the request to fork a new application.
2. Zygote gets a request, it forks and run the new process in a new
   mount namespace, say "new mnt ns".

The file opened in step 0 ties to the mount point in "old mnt ns". The
mnt_id of that mount is listed in /proc/pid/fdinfo. However,
/proc/pid/mountinfo points to current ns, i.e., "new mnt ns".

Althgouh this issue is exposed in Android, we believe it's generic.
Prcoess may open files and enter new mnt ns.

To address it, this patch searches the mirror mount in current ns with
MAJOR and MINOR and shows the mirror's mnt_id.

v2: fix warning reported by lkp

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Chen, Hu <hu1.chen@intel.com>
---
 fs/mount.h     |  2 ++
 fs/namespace.c | 30 ++++++++++++++++++++++++++++++
 fs/proc/fd.c   | 12 ++++++++++--
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index 711a4093e475..6bbfc2b3b8ba 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -153,3 +153,5 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
 {
 	return ns->seq == 0;
 }
+
+extern struct mount *lookup_mirror_mnt(const struct mount *mnt);
diff --git a/fs/namespace.c b/fs/namespace.c
index 2adfe7b166a3..131b36517472 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -683,6 +683,36 @@ bool __is_local_mountpoint(struct dentry *dentry)
 	return is_covered;
 }
 
+/*
+ * lookup_mirror_mnt - Return @mnt's mirror mount in the current/local mount
+ * namespace. If mirror isn't found, just return NULL.
+ */
+struct mount *lookup_mirror_mnt(const struct mount *mnt)
+{
+	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
+	struct mount *mnt_local;
+	bool is_matched = false;
+
+	/* mnt belongs to current namesapce */
+	if (mnt->mnt_ns == ns)
+		return (struct mount *) mnt;
+
+	down_read(&namespace_sem);
+	list_for_each_entry(mnt_local, &ns->list, mnt_list) {
+		struct super_block *sb = mnt->mnt.mnt_sb;
+		struct super_block *sb_local = mnt_local->mnt.mnt_sb;
+
+		if (MAJOR(sb->s_dev) == MAJOR(sb_local->s_dev) &&
+		    MINOR(sb->s_dev) == MINOR(sb_local->s_dev)) {
+			is_matched = true;
+			break;
+		}
+	}
+	up_read(&namespace_sem);
+
+	return is_matched ? mnt_local : NULL;
+}
+
 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
 {
 	struct hlist_head *chain = mp_hash(dentry);
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 81882a13212d..cbf2571b0620 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -23,6 +23,7 @@ static int seq_show(struct seq_file *m, void *v)
 	int f_flags = 0, ret = -ENOENT;
 	struct file *file = NULL;
 	struct task_struct *task;
+	struct mount *mount = NULL;
 
 	task = get_proc_task(m->private);
 	if (!task)
@@ -53,9 +54,16 @@ static int seq_show(struct seq_file *m, void *v)
 	if (ret)
 		return ret;
 
+	/* After unshare -m, real_mount(file->f_path.mnt) is not meaningful in
+	 * current mount namesapce. We want to know the mnt_id in current mount
+	 * namespace
+	 */
+	mount = lookup_mirror_mnt(real_mount(file->f_path.mnt));
+	if (!mount)
+		mount = real_mount(file->f_path.mnt);
+
 	seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
-		   (long long)file->f_pos, f_flags,
-		   real_mount(file->f_path.mnt)->mnt_id);
+		   (long long)file->f_pos, f_flags, mount->mnt_id);
 
 	show_fd_locks(m, file, files);
 	if (seq_has_overflowed(m))
-- 
2.22.0