[PATCH 1/2] fs/proc: show correct device and inode numbers in /proc/pid/maps

[Andrei Vagin <avagin@google.com>]

Device and inode numbers in /proc/pid/maps have to match numbers returned by
statx for the same files.

/proc/pid/maps shows device and inode numbers of vma->vm_file-s. Here is
an issue. If a mapped file is on a stackable file system (e.g.,
overlayfs), vma->vm_file is a backing file whose f_inode is on the
underlying filesystem. To show correct numbers, we need to get a user
file and shows its numbers. The same trick is used to show file paths in
/proc/pid/maps.

But it isn't the end of this story. A file system can manipulate inode numbers
within the getattr callback (e.g., ovl_getattr), so vfs_getattr must be used to
get correct numbers.

Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Alexander Mikhalitsyn <alexander@mihalicyn.com>
Signed-off-by: Andrei Vagin <avagin@google.com>
---
 fs/proc/task_mmu.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 435b61054b5b..abbf96c091ad 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -273,9 +273,23 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
 	const char *name = NULL;
 
 	if (file) {
-		struct inode *inode = file_inode(vma->vm_file);
-		dev = inode->i_sb->s_dev;
-		ino = inode->i_ino;
+		const struct path *path;
+		struct kstat stat;
+
+		path = file_user_path(file);
+		/*
+		 * A file system can manipulate inode numbers within the
+		 * getattr callback (e.g. ovl_getattr).
+		 */
+		if (!vfs_getattr_nosec(path, &stat, STATX_INO, AT_STATX_DONT_SYNC)) {
+			dev = stat.dev;
+			ino = stat.ino;
+		} else {
+			struct inode *inode = d_backing_inode(path->dentry);
+
+			dev = inode->i_sb->s_dev;
+			ino = inode->i_ino;
+		}
 		pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;
 	}
 
-- 
2.43.0.472.g3155946c3a-goog