[PATCH net] net/llc: avoid BUG_ON() in skb_orphan()

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

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 <eduma...@google.com>
Reported-by: Andrey Konovalov <andreyk...@google.com>
---
 net/llc/llc_conn.c |    3 +++
 net/llc/llc_sap.c  |    3 +++
 2 files changed, 6 insertions(+)

diff --git a/net/llc/llc_conn.c b/net/llc/llc_conn.c
index 
3e821daf9dd4a2fbf00550591e92b153efd4a73a..8bc5a1bd2d453542df31506f543feb64b64cdd96
 100644
--- 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 
d0e1e804ebd73dcebcf2f930b921233a49b0f454..5404d0d195cc581613e356b75bd70321e617673e
 100644
--- a/net/llc/llc_sap.c
+++ b/net/llc/llc_sap.c
@@ -290,7 +290,10 @@ 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);
 }