[PATCH] fs: prevent data-race due to missing inode_lock when calling vfs_getattr

[Jeongjun Park <aha310510@gmail.com>]

Many filesystems lock inodes before calling vfs_getattr, so there is no
data-race for inodes. However, some functions in fs/stat.c that call
vfs_getattr do not lock inodes, so the data-race occurs.

Therefore, we need to apply a patch to remove the long-standing data-race
for inodes in some functions that do not lock inodes.

Cc: <stable@vger.kernel.org>
Fixes: da9aa5d96bfe ("fs: remove vfs_statx_fd")
Fixes: 0ef625bba6fb ("vfs: support statx(..., NULL, AT_EMPTY_PATH, ...)")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 fs/stat.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/stat.c b/fs/stat.c
index 41e598376d7e..da532b611aa3 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -220,13 +220,21 @@ EXPORT_SYMBOL(vfs_getattr);
  */
 int vfs_fstat(int fd, struct kstat *stat)
 {
+	const struct path *path;
+	struct inode *inode;
 	struct fd f;
 	int error;
 
 	f = fdget_raw(fd);
 	if (!fd_file(f))
 		return -EBADF;
-	error = vfs_getattr(&fd_file(f)->f_path, stat, STATX_BASIC_STATS, 0);
+
+	path = &fd_file(f)->f_path;
+	inode = d_backing_inode(path->dentry);
+
+	inode_lock_shared(inode);
+	error = vfs_getattr(path, stat, STATX_BASIC_STATS, 0);
+	inode_unlock_shared(inode);
 	fdput(f);
 	return error;
 }
@@ -248,7 +256,11 @@ int getname_statx_lookup_flags(int flags)
 static int vfs_statx_path(struct path *path, int flags, struct kstat *stat,
 			  u32 request_mask)
 {
+	struct inode *inode = d_backing_inode(path->dentry);
+
+	inode_lock_shared(inode);
 	int error = vfs_getattr(path, stat, request_mask, flags);
+	inode_unlock_shared(inode);
 
 	if (request_mask & STATX_MNT_ID_UNIQUE) {
 		stat->mnt_id = real_mount(path->mnt)->mnt_id_unique;
--