Bluetooth: Prevent buffer overflow in l2cap config request

commit 7ac28817536797fd40e9646452183606f9e17f71 upstream.

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.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 514aa8fbbee20989db0d0c4af0cd5ad46c3c917e..71120ee8511e8e07277220dbae719b54840a4549 100644 (file)
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -2720,7 +2720,7 @@ 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 (l2cap_pi(sk)->conf_len + len > sizeof(l2cap_pi(sk)->conf_req)) {
+       if (len < 0 || l2cap_pi(sk)->conf_len + len > sizeof(l2cap_pi(sk)->conf_req)) {
                l2cap_send_cmd(conn, cmd->ident, L2CAP_CONF_RSP,
                                l2cap_build_conf_rsp(sk, rsp,
                                        L2CAP_CONF_REJECT, flags), rsp);