[PATCH v2] ovl: do not generate duplicate fsnotify events for "fake" path

[Amir Goldstein <amir73il@gmail.com>]

Overlayfs "fake" path is used for stacked file operations on
underlying files.  Operations on files with "fake" path must not
generate fsnotify events with path data, because those events have
already been generated at overlayfs layer and because the reported
event->fd for fanotify marks on underlying inode/filesystem will
have the wrong path (the overlayfs path).

Link: https://lore.kernel.org/linux-fsdevel/20190423065024.12695-1-jencce.kernel@gmail.com/
Reported-by: Murphy Zhou <jencce.kernel@gmail.com>
Fixes: d1d04ef8572b ("ovl: stack file ops")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---

Miklos,

V1 was addressed to Jan and was trying to teach fsnotify about fake path.
V2 leaves fsnotify subsystem alone and just sets the FMODE_NONOTIFY
flag on realfile. All the rest of the complications with mark mounts
are irrelevant.

Same extended fanotify06 that was used to verify V1 also verified V2.

Thanks,
Amir.

 fs/overlayfs/file.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index ddfd93f13cc5..7d2f01957e40 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -29,10 +29,11 @@ static struct file *ovl_open_realfile(const struct file *file,
 	struct inode *inode = file_inode(file);
 	struct file *realfile;
 	const struct cred *old_cred;
+	int flags = file->f_flags | O_NOATIME | FMODE_NONOTIFY;
 
 	old_cred = ovl_override_creds(inode->i_sb);
-	realfile = open_with_fake_path(&file->f_path, file->f_flags | O_NOATIME,
-				       realinode, current_cred());
+	realfile = open_with_fake_path(&file->f_path, flags, realinode,
+				       current_cred());
 	revert_creds(old_cred);
 
 	pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
@@ -50,7 +51,7 @@ static int ovl_change_flags(struct file *file, unsigned int flags)
 	int err;
 
 	/* No atime modificaton on underlying */
-	flags |= O_NOATIME;
+	flags |= O_NOATIME | FMODE_NONOTIFY;
 
 	/* If some flag changed that cannot be changed then something's amiss */
 	if (WARN_ON((file->f_flags ^ flags) & ~OVL_SETFL_MASK))
-- 
2.17.1