Re: [PATCH] cifs: check if mid was deleted in async read callback

[Paulo Alcantara <pc@cjr.nz>]

Enzo Matsumiya <ematsumiya@suse.de> writes:

> There's a race when cifs_readv_receive() might dequeue the mid,
> and mid->callback(), called from demultiplex thread, will try to
> access it to verify the signature before the mid is actually
> released/deleted.
>
> Currently the signature verification fails, but the verification
> shouldn't have happened at all because the mid was deleted because
> of an error, and hence not really supposed to be passed to
> ->callback(). There are no further errors because the mid is
> effectivelly gone by the end of the callback.
>
> This patch checks if the mid doesn't have the MID_DELETED flag set (by
> dequeue_mid()) right before trying to verify the signature. According to
> my tests, trying to check it earlier, e.g. after the ->receive() call in
> cifs_demultiplex_thread, will fail most of the time as dequeue_mid()
> might not have been called yet.
>
> This behaviour can be seen in xfstests generic/465, for example, where
> mids with STATUS_END_OF_FILE (-ENODATA) are dequeued and supposed to be
> discarded, but instead have their signature computed, but mismatched.
>
> Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
> ---
>  fs/cifs/cifssmb.c | 2 +-
>  fs/cifs/smb2pdu.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)

Good catch!

Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>