Re: FAILED: patch "[PATCH] cifs: Fix preauth hash corruption" failed to apply to 4.19-stable tree

[Aurélien Aptel <aaptel@xxxxxxxx>]

Hi Greg,

<gregkh@xxxxxxxxxxxxxxxxxxx> writes:
> 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@xxxxxxxxxxxxxxx>.

This should apply for 4.19.

For 4.14 you can drop the patch, it predates preauth hash implementation.

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

>From a844f9f9a55fb6a100aee7c517f87c116c5866d8 Mon Sep 17 00:00:00 2001
From: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
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@xxxxxxxx>
CC: <stable@xxxxxxxxxxxxxxx>
Reviewed-by: Aurelien Aptel <aaptel@xxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>

[aaptel: backport to kernel without CIFS_SESS_OP and multichannel]
Signed-off-by: Aurelien Aptel <aaptel@xxxxxxxx>
---
 fs/cifs/transport.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 70412944b267..59643acb6d67 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -891,9 +891,12 @@ 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))
+	if ((ses->status == CifsNew) || (optype & CIFS_NEG_OP)) {
+		mutex_lock(&ses->server->srv_mutex);
 		smb311_update_preauth_hash(ses, rqst[0].rq_iov,
 					   rqst[0].rq_nvec);
+		mutex_unlock(&ses->server->srv_mutex);
+	}
 
 	if (timeout == CIFS_ASYNC_OP)
 		goto out;
@@ -964,7 +967,9 @@ 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(&ses->server->srv_mutex);
 		smb311_update_preauth_hash(ses, &iov, 1);
+		mutex_unlock(&ses->server->srv_mutex);
 	}
 
 out:
-- 
2.30.0

Cheers,
-- 
Aurélien Aptel / SUSE Labs Samba Team
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