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fs/proc: show correct device and inode numbers in /proc/pid/maps 

/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.

Cc: Alexander Mikhalitsyn <alexander@mihalicyn.com>
Suggested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Andrei Vagin <avagin@google.com>
Link: https://lore.kernel.org/r/20231214064439.1023011-1-avagin@google.com
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Andrei Vagin 2023-12-13 22:44:38 -08:00 committed by Christian Brauner
parent 4342252300
commit 3efdc78fdc
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GPG Key ID: 91C61BC06578DCA2
2 changed files with 15 additions and 6 deletions
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3
fs/proc/task_mmu.c
View File

@ -273,7 +273,8 @@ 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);
const struct inode *inode = file_user_inode(vma->vm_file);
dev = inode->i_sb->s_dev;
ino = inode->i_ino;
pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;

18
include/linux/fs.h
View File

@ -2523,20 +2523,28 @@ struct file *backing_file_open(const struct path *user_path, int flags,
struct path *backing_file_user_path(struct file *f);
/*
* file_user_path - get the path to display for memory mapped file
*
* When mmapping a file on a stackable filesystem (e.g., overlayfs), the file
* stored in ->vm_file is a backing file whose f_inode is on the underlying
* filesystem. When the mapped file path is displayed to user (e.g. via
* /proc/<pid>/maps), this helper should be used to get the path to display
* to the user, which is the path of the fd that user has requested to map.
* filesystem. When the mapped file path and inode number are displayed to
* user (e.g. via /proc/<pid>/maps), these helpers should be used to get the
* path and inode number to display to the user, which is the path of the fd
* that user has requested to map and the inode number that would be returned
* by fstat() on that same fd.
*/
/* Get the path to display in /proc/<pid>/maps */
static inline const struct path *file_user_path(struct file *f)
{
if (unlikely(f->f_mode & FMODE_BACKING))
return backing_file_user_path(f);
return &f->f_path;
}
/* Get the inode whose inode number to display in /proc/<pid>/maps */
static inline const struct inode *file_user_inode(struct file *f)
{
if (unlikely(f->f_mode & FMODE_BACKING))
return d_inode(backing_file_user_path(f)->dentry);
return file_inode(f);
}
static inline struct file *file_clone_open(struct file *file)
{