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

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>

2 files changed, 6 insertions, 0 deletions

diff --git a/net/llc/llc_conn.c b/net/llc/llc_conn.c
index 3e821daf9dd4..8bc5a1bd2d45 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 d0e1e804ebd7..5404d0d195cc 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);
 }