net/llc: avoid BUG_ON() in skb_orphan()

commit 8b74d439e1697110c5e5c600643e823eb1dd0762 upstream.

It seems nobody used LLC since linux-3.12.

Fortunately fuzzers like syzkaller still know how to run this code,
otherwise it would be no fun.

Setting skb->sk without skb->destructor leads to all kinds of
bugs, we now prefer to be very strict about it.

Ideally here we would use skb_set_owner() but this helper does not exist yet,
only CAN seems to have a private helper for that.

Fixes: 376c7311bdb6 ("net: add a temporary sanity check in skb_orphan()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/llc/llc_conn.c b/net/llc/llc_conn.c
index ba137a6..f3125b9 100644 (file)
--- a/net/llc/llc_conn.c
+++ b/net/llc/llc_conn.c
@@ -821,7 +821,10 @@ void llc_conn_handler(struct llc_sap *sap, struct sk_buff *skb)
                 * another trick required to cope with how the PROCOM state
                 * machine works. -acme
                 */
+               skb_orphan(skb);
+               sock_hold(sk);
                skb->sk = sk;
+               skb->destructor = sock_efree;
        }
        if (!sock_owned_by_user(sk))
                llc_conn_rcv(sk, skb);

diff --git a/net/llc/llc_sap.c b/net/llc/llc_sap.c
index 94e7fca..687fe74 100644 (file)
--- a/net/llc/llc_sap.c
+++ b/net/llc/llc_sap.c
@@ -294,7 +294,10 @@ static void llc_sap_rcv(struct llc_sap *sap, struct sk_buff *skb,
 
        ev->type   = LLC_SAP_EV_TYPE_PDU;
        ev->reason = 0;
+       skb_orphan(skb);
+       sock_hold(sk);
        skb->sk = sk;
+       skb->destructor = sock_efree;
        llc_sap_state_process(sap, skb);
 }