From: Roberto Bergantinos Corpas <rbergant@redhat.com>
Date: Mon, 14 Oct 2019 10:59:23 +0200
Subject: CIFS: avoid using MID 0xFFFF
Git-commit: 03d9a9fe3f3aec508e485dd3dcfa1e99933b4bdb
Patch-mainline: 5.4-rc5
References: bnc#1151927 5.3.8

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 fs/cifs/smb1ops.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/fs/cifs/smb1ops.c
+++ b/fs/cifs/smb1ops.c
@@ -171,6 +171,9 @@ cifs_get_next_mid(struct TCP_Server_Info
 	/* 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.