linux-kernel - [PATCH 3.16 032/202] cifs: Fix potential OOB access of lock element array

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Message-ID: <lsq.1556377989.596434863@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Steve French" <stfrench@...rosoft.com>,
        "Ross Lagerwall" <ross.lagerwall@...rix.com>
Subject: [PATCH 3.16 032/202] cifs: Fix potential OOB access of lock
 element array

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ross Lagerwall <ross.lagerwall@...rix.com>

commit b9a74cde94957d82003fb9f7ab4777938ca851cd upstream.

If maxBuf is small but non-zero, it could result in a zero sized lock
element array which we would then try and access OOB.

Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/cifs/file.c     | 8 ++++----
 fs/cifs/smb2file.c | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1066,10 +1066,10 @@ cifs_push_mandatory_locks(struct cifsFil
 
 	/*
 	 * Accessing maxBuf is racy with cifs_reconnect - need to store value
-	 * and check it for zero before using.
+	 * and check it before using.
 	 */
 	max_buf = tcon->ses->server->maxBuf;
-	if (!max_buf) {
+	if (max_buf < (sizeof(struct smb_hdr) + sizeof(LOCKING_ANDX_RANGE))) {
 		free_xid(xid);
 		return -EINVAL;
 	}
@@ -1403,10 +1403,10 @@ cifs_unlock_range(struct cifsFileInfo *c
 
 	/*
 	 * Accessing maxBuf is racy with cifs_reconnect - need to store value
-	 * and check it for zero before using.
+	 * and check it before using.
 	 */
 	max_buf = tcon->ses->server->maxBuf;
-	if (!max_buf)
+	if (max_buf < (sizeof(struct smb_hdr) + sizeof(LOCKING_ANDX_RANGE)))
 		return -EINVAL;
 
 	max_num = (max_buf - sizeof(struct smb_hdr)) /
--- a/fs/cifs/smb2file.c
+++ b/fs/cifs/smb2file.c
@@ -101,10 +101,10 @@ smb2_unlock_range(struct cifsFileInfo *c
 
 	/*
 	 * Accessing maxBuf is racy with cifs_reconnect - need to store value
-	 * and check it for zero before using.
+	 * and check it before using.
 	 */
 	max_buf = tcon->ses->server->maxBuf;
-	if (!max_buf)
+	if (max_buf < sizeof(struct smb2_lock_element))
 		return -EINVAL;
 
 	max_num = max_buf / sizeof(struct smb2_lock_element);