[PATCH 3.12 071/113] net/llc: avoid BUG_ON() in skb_orphan()

[Jiri Slaby]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ 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.

[js] take sock_efree from 62bccb8cdb6905

Fixes: 376c7311bdb6 ("net: add a temporary sanity check in skb_orphan()")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 include/net/sock.h | 1 +
 net/core/sock.c    | 6 ++++++
 net/llc/llc_conn.c | 3 +++
 net/llc/llc_sap.c  | 3 +++
 4 files changed, 13 insertions(+)

diff --git a/include/net/sock.h b/include/net/sock.h
index 238e934dd3c3..467d2f810fb3 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1554,6 +1554,7 @@ extern struct sk_buff		*sock_rmalloc(struct sock *sk,
 extern void			sock_wfree(struct sk_buff *skb);
 extern void			skb_orphan_partial(struct sk_buff *skb);
 extern void			sock_rfree(struct sk_buff *skb);
+void sock_efree(struct sk_buff *skb);
 extern void			sock_edemux(struct sk_buff *skb);
 
 extern int			sock_setsockopt(struct socket *sock, int level,
diff --git a/net/core/sock.c b/net/core/sock.c
index 7fa427ed41bc..d765d6411a5b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1656,6 +1656,12 @@ void sock_rfree(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(sock_rfree);
 
+void sock_efree(struct sk_buff *skb)
+{
+	sock_put(skb->sk);
+}
+EXPORT_SYMBOL(sock_efree);
+
 void sock_edemux(struct sk_buff *skb)
 {
 	struct sock *sk = skb->sk;
diff --git a/net/llc/llc_conn.c b/net/llc/llc_conn.c
index cd8724177965..6d36b3241b98 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 e5850699098e..4ee1e1142e8e 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);
 }
 
-- 
2.12.0