Bluetooth: Prevent buffer overflow in l2cap config request

A remote user can provide a small value for the command size field in the command header of an l2cap configuration request, resulting in an integer underflow when subtracting the size of the configuration request header. This results in copying a very large amount of data via memcpy() and destroying the kernel heap. Check for underflow.

---
 net/bluetooth/l2cap_core.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index e64a1c2..06ea272 100644
@@ -2334,7 +2334,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr
 
 	/* Reject if config buffer is too small. */
 	len = cmd_len - sizeof(*req);
-	if (chan->conf_len + len > sizeof(chan->conf_req)) {
+	if (len < 0 || chan->conf_len + len > sizeof(chan->conf_req)) {
 		l2cap_send_cmd(conn, cmd->ident, L2CAP_CONF_RSP,
 				l2cap_build_conf_rsp(chan, rsp,
 					L2CAP_CONF_REJECT, flags), rsp);

Hi Dan,

Applied, thanks.

Gustavo