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CIFS: avoid using MID 0xFFFF

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According to MS-CIFS specification MID 0xFFFF should not be used by the
CIFS client, but we actually do. Besides, this has proven to cause races
leading to oops between SendReceive2/cifs_demultiplex_thread. On SMB1,
MID is a 2 byte value easy to reach in CurrentMid which may conflict with
an oplock break notification request coming from server

Signed-off-by: Roberto Bergantinos Corpas <rbergant@redhat.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>
This commit is contained in:
Roberto Bergantinos Corpas 2019-10-14 10:59:23 +02:00 committed by Steve French
parent 553292a634
commit 03d9a9fe3f
1 changed files with 3 additions and 0 deletions
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3
fs/cifs/smb1ops.c
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@ -171,6 +171,9 @@ cifs_get_next_mid(struct TCP_Server_Info *server)
/* we do not want to loop forever */
last_mid = cur_mid;
cur_mid++;
/* avoid 0xFFFF MID */
if (cur_mid == 0xffff)
cur_mid++;
/*
* This nested loop looks more expensive than it is.