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

[Enzo Matsumiya <ematsumiya@suse.de>]

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(-)

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index addf3fc62aef..116f6afe33c6 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -1308,7 +1308,7 @@ cifs_readv_callback(struct mid_q_entry *mid)
 	switch (mid->mid_state) {
 	case MID_RESPONSE_RECEIVED:
 		/* result already set, check signature */
-		if (server->sign) {
+		if (server->sign && !(mid->mid_flags & MID_DELETED)) {
 			int rc = 0;
 
 			rc = cifs_verify_signature(&rqst, server,
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 5da0b596c8a0..394996c4f729 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -4136,7 +4136,7 @@ smb2_readv_callback(struct mid_q_entry *mid)
 		credits.value = le16_to_cpu(shdr->CreditRequest);
 		credits.instance = server->reconnect_instance;
 		/* result already set, check signature */
-		if (server->sign && !mid->decrypted) {
+		if (server->sign && !mid->decrypted && !(mid->mid_flags & MID_DELETED)) {
 			int rc;
 
 			rc = smb2_verify_signature(&rqst, server);
-- 
2.35.3