[PATCH 3.18 057/145] net/llc: avoid BUG_ON() in skb_orphan()

Greg Kroah-Hartman
2017-04-16T11:16:07Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 8b74d439e1697110c5e5c600643e823eb1dd0762 ]

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/llc/llc_conn.c | 3 +++
net/llc/llc_sap.c | 3 +++
2 files changed, 6 insertions(+)

--- a/net/llc/llc_conn.c
+++ b/net/llc/llc_conn.c
@@ -821,7 +821,10 @@ void llc_conn_handler(struct llc_sap *sa
* 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);
--- a/net/llc/llc_sap.c
+++ b/net/llc/llc_sap.c
@@ -290,7 +290,10 @@ static void llc_sap_rcv(struct llc_sap *

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);
}