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>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 9610a9c85b9896e69cd6c62712cb5f8376a33040..fed5d8bb1be66916cc074b3dd08277a4d16c2ed2 100644 (file)
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -1737,7 +1737,7 @@ 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);