On Tue 25-04-17 14:29:35, Amir Goldstein wrote:
> When delivering an event to userspace for a file on an NFS share,
> if the file is deleted on server side before user reads the event,
> user will not get the event.
>
> If the event queue contained several events, the stale event is
> quietly dropped and read() returns to user with events read so far
> in the buffer.
>
> If the event queue contains a single stale event or if the stale
> event is a permission event, read() returns to user with the kernel
> internal error code 518 (EOPENSTALE), which is not a POSIX error code.
>
> Check the internal return value -EOPENSTALE in fanotify_read(), just
> the same as it is checked in path_openat() and drop the event in the
> cases that it is not already dropped.
>
> This is a reproducer from Marko Rauhamaa:
>
> Just take the example program listed under "man fanotify" ("fantest")
> and follow these steps:
>
> ==============================================================
> NFS Server NFS Client(1) NFS Client(2)
> ==============================================================
> # echo foo >/nfsshare/bar.txt
> # cat /nfsshare/bar.txt
> foo
> # ./fantest /nfsshare
> Press enter key to terminate.
> Listening for events.
> # rm -f /nfsshare/bar.txt
> # cat /nfsshare/bar.txt
> read: Unknown error 518
> cat: /nfsshare/bar.txt: Operation not permitted
> ==============================================================
>
> where NFS Client (1) and (2) are two terminal sessions on a single NFS
> Client machine.
>
> Reported-by: Marko Rauhamaa <marko.rauhamaa@xxxxxxxxxxxx>
> Tested-by: Marko Rauhamaa <marko.rauhamaa@xxxxxxxxxxxx>
> Cc: <linux-api@xxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/notify/fanotify/fanotify_user.c | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> Jan,
>
> This is v2 patch that was tested by Marko.
> It includes your fix to my v1 patch.
>
> Marko tested both blocking and non-blocking fanotify fd.
> I did not test with stale NFS files myself, but I did test by emulating
> stale NFS files with orphan files, using this test patch to create_fd():
>
> put_unused_fd(client_fd);
> client_fd = PTR_ERR(new_file);
> > } else if (!event->path.dentry->d_inode ||
> > !event->path.dentry->d_inode->i_nlink) {
> > put_unused_fd(client_fd);
> > fput(new_file);
> > return -EOPENSTALE;
> } else {
> *file = new_file;
> }
>
> I CC'ed linux-api in case Michael would want to add a BUGS note on this
> and CC'ed stable because we should consider patching this bug in older
> kernels. After all, Marko discovered this bug in a RHEL kernel.
Thanks! I've merged the patch to my tree and will push it to Linus during
the merge window.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
