Bluetooth: Fix potential double-frees of L2CAP skbs

The l2cap_recv_frame function is expected to take ownership and
eventually free the skb passed to it. We need to ensure that the
conn->rx_skb pointer is no longer reachable when calling
l2cap_recv_frame so that no other function, such as l2cap_conn_del, may
think that it can free conn->rx_skb.

An actual situation when this can happen is when smp_sig_channel (called
from l2cap_recv_frame) fails and l2cap_conn_del gets called as a
consequence. The l2cap_conn_del function would then try to free
conn->rx_skb, but as the same skb was just passed to smp_sig_channel and
freed we get a double-free.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index a9a7df6639a7..06e7173c2d13 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -6798,9 +6798,13 @@ int l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
                 conn->rx_len -= skb->len;
 
                 if (!conn->rx_len) {
-                        /* Complete frame received */
-                        l2cap_recv_frame(conn, conn->rx_skb);
+                        /* Complete frame received. l2cap_recv_frame
+                         * takes ownership of the skb so set the global
+                         * rx_skb pointer to NULL first.
+                         */
+                        struct sk_buff *rx_skb = conn->rx_skb;
                         conn->rx_skb = NULL;
+                        l2cap_recv_frame(conn, rx_skb);
                 }
                 break;
         }