From b9a74cde94957d82003fb9f7ab4777938ca851cd Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <ross.lagerwall@citrix.com>
Date: Tue, 8 Jan 2019 18:30:57 +0000
Subject: [PATCH] cifs: Fix potential OOB access of lock element array
Git-commit: b9a74cde94957d82003fb9f7ab4777938ca851cd
Patch-mainline: v5.0-rc2
References: bsc#1051510, bsc#1144333

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>
Acked-by: Paulo Alcantara <palcantara@suse.de>
---
 fs/cifs/file.c     | 8 ++++----
 fs/cifs/smb2file.c | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 673f948e4760..5b6f8392d9db 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1132,10 +1132,10 @@ cifs_push_mandatory_locks(struct cifsFileInfo *cfile)
 
 	/*
 	 * 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;
 	}
@@ -1476,10 +1476,10 @@ cifs_unlock_range(struct cifsFileInfo *cfile, struct file_lock *flock,
 
 	/*
 	 * 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;
 
 	BUILD_BUG_ON(sizeof(struct smb_hdr) + sizeof(LOCKING_ANDX_RANGE) >
diff --git a/fs/cifs/smb2file.c b/fs/cifs/smb2file.c
index eff01ed6db0a..b204e84b87fb 100644
--- a/fs/cifs/smb2file.c
+++ b/fs/cifs/smb2file.c
@@ -122,10 +122,10 @@ smb2_unlock_range(struct cifsFileInfo *cfile, struct file_lock *flock,
 
 	/*
 	 * 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;
 
 	BUILD_BUG_ON(sizeof(struct smb2_lock_element) > PAGE_SIZE);
-- 
2.16.4