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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Ross Lagerwall <ross.lagerwall@citrix.com>,
        Steve French <stfrench@microsoft.com>
Subject: [PATCH 4.9 03/16] cifs: Fix potential OOB access of lock element array
Date:   Tue, 15 Jan 2019 17:35:46 +0100
Message-Id: <20190115154848.502629068@linuxfoundation.org>
In-Reply-To: <20190115154848.164648613@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Ross Lagerwall <ross.lagerwall@citrix.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@citrix.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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
@@ -1118,10 +1118,10 @@ 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;
 	}
@@ -1456,10 +1456,10 @@ 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
@@ -123,10 +123,10 @@ 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);