When the lowerdir of an overlayfs is a merged directory of another overlayfs, ovl_open_realfile() will fail to open the real file and point to a lower dentry copy, without the proper parent path. After this, d_path() will then display the path incorrectly as if the file is placed in the root directory. This bug can be triggered with the following setup: mkdir -p ovl-A/lower ovl-A/upper ovl-A/merge ovl-A/work mkdir -p ovl-B/upper ovl-B/merge ovl-B/work cp /bin/cat ovl-A/lower/ mount -t overlay overlay -o \ lowerdir=ovl-A/lower,upperdir=ovl-A/upper,workdir=ovl-A/work \ ovl-A/merge mount -t overlay overlay -o \ lowerdir=ovl-A/merge,upperdir=ovl-B/upper,workdir=ovl-B/work \ ovl-B/merge ovl-A/merge/cat /proc/self/maps | grep --color cat ovl-B/merge/cat /proc/self/maps | grep --color cat The first cat will correctly show `/ovl-A/merge/cat`, while the second one shows just `/cat`. To fix that, uses file_user_path() inside of backing_file_open() to get the correct file path for the dentry. Co-developed-by: John Schoenick <johns@xxxxxxxxxxxxxxxxx> Signed-off-by: John Schoenick <johns@xxxxxxxxxxxxxxxxx> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx> --- fs/overlayfs/file.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index 969b458100fe..dfea7bd800cb 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -48,8 +48,8 @@ static struct file *ovl_open_realfile(const struct file *file, if (!inode_owner_or_capable(real_idmap, realinode)) flags &= ~O_NOATIME; - realfile = backing_file_open(&file->f_path, flags, realpath, - current_cred()); + realfile = backing_file_open(file_user_path((struct file *) file), + flags, realpath, current_cred()); } ovl_revert_creds(old_cred); -- 2.49.0
