[PATCH 3.16 238/328] cifs: integer overflow in in SMB2_ioctl()

[Ben Hutchings]

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

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

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

commit 2d204ee9d671327915260071c19350d84344e096 upstream.

The "le32_to_cpu(rsp->OutputOffset) + *plen" addition can overflow and
wrap around to a smaller value which looks like it would lead to an
information leak.

Fixes: 4a72dafa19ba ("SMB2 FSCTL and IOCTL worker function")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Reviewed-by: Aurelien Aptel <aaptel@xxxxxxxx>
[bwh: Backported to 3.16: Use get_rfc1002_length(rsp) instead of
 rsp->iov.iov_len]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/cifs/smb2pdu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -1394,14 +1394,14 @@ SMB2_ioctl(const unsigned int xid, struc
 	/* We check for obvious errors in the output buffer length and offset */
 	if (*plen == 0)
 		goto ioctl_exit; /* server returned no data */
-	else if (*plen > 0xFF00) {
+	else if (*plen > get_rfc1002_length(rsp) || *plen > 0xFF00) {
 		cifs_dbg(VFS, "srv returned invalid ioctl length: %d\n", *plen);
 		*plen = 0;
 		rc = -EIO;
 		goto ioctl_exit;
 	}
 
-	if (get_rfc1002_length(rsp) < le32_to_cpu(rsp->OutputOffset) + *plen) {
+	if (get_rfc1002_length(rsp) - *plen < le32_to_cpu(rsp->OutputOffset)) {
 		cifs_dbg(VFS, "Malformed ioctl resp: len %d offset %d\n", *plen,
 			le32_to_cpu(rsp->OutputOffset));
 		*plen = 0;