The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 05946d4b7a7349ae58bfa2d51ae832e64a394c2d Mon Sep 17 00:00:00 2001

From: Vincent Whitchurch vincent.whitchurch@axis.com Date: Wed, 10 Mar 2021 13:20:40 +0100 Subject: [PATCH] cifs: Fix preauth hash corruption

smb311_update_preauth_hash() uses the shash in server->secmech without appropriate locking, and this can lead to sessions corrupting each other's preauth hashes.

The following script can easily trigger the problem:

#!/bin/sh -e

NMOUNTS=10 for i in $(seq $NMOUNTS); mkdir -p /tmp/mnt$i umount /tmp/mnt$i 2>/dev/null || : done while :; do for i in $(seq $NMOUNTS); do mount -t cifs //192.168.0.1/test /tmp/mnt$i -o ... & done wait for i in $(seq $NMOUNTS); do umount /tmp/mnt$i done done

Usually within seconds this leads to one or more of the mounts failing with the following errors, and a "Bad SMB2 signature for message" is seen in the server logs:

CIFS: VFS: \192.168.0.1 failed to connect to IPC (rc=-13) CIFS: VFS: cifs_mount failed w/return code = -13

Fix it by holding the server mutex just like in the other places where the shashes are used.

Fixes: 8bd68c6e47abff34e4 ("CIFS: implement v3.11 preauth integrity") Signed-off-by: Vincent Whitchurch vincent.whitchurch@axis.com CC: stable@vger.kernel.org Reviewed-by: Aurelien Aptel aaptel@suse.com Signed-off-by: Steve French stfrench@microsoft.com

diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c index 007d99437c77..c1725b55f364 100644 --- a/fs/cifs/transport.c +++ b/fs/cifs/transport.c @@ -1196,9 +1196,12 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses, /* * Compounding is never used during session establish. */ - if ((ses->status == CifsNew) || (optype & CIFS_NEG_OP) || (optype & CIFS_SESS_OP)) + if ((ses->status == CifsNew) || (optype & CIFS_NEG_OP) || (optype & CIFS_SESS_OP)) { + mutex_lock(&server->srv_mutex); smb311_update_preauth_hash(ses, rqst[0].rq_iov, rqst[0].rq_nvec); + mutex_unlock(&server->srv_mutex); + }

for (i = 0; i < num_rqst; i++) { rc = wait_for_response(server, midQ[i]); @@ -1266,7 +1269,9 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses, .iov_base = resp_iov[0].iov_base, .iov_len = resp_iov[0].iov_len }; + mutex_lock(&server->srv_mutex); smb311_update_preauth_hash(ses, &iov, 1); + mutex_unlock(&server->srv_mutex); }

out: