netdev - [PATCH net] phonet: properly unshare skbs in phonet

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Message-ID: <1452617880.1223.21.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 12 Jan 2016 08:58:00 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Remi Denis-Courmont <courmisch@...il.com>
Cc:	Salam Noureddine <noureddine@...sta.com>,
	"David S. Miller" <davem@...emloft.net>,
	Pali Rohár <pali.rohar@...il.com>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Sebastian Reichel <sre@...nel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: [PATCH net] phonet: properly unshare skbs in phonet_rcv()

From: Eric Dumazet <edumazet@...gle.com>

Ivaylo Dimitrov reported a regression caused by commit 7866a621043f
("dev: add per net_device packet type chains").

skb->dev becomes NULL and we crash in __netif_receive_skb_core().

Before above commit, different kind of bugs or corruptions could happen
without major crash.

But the root cause is that phonet_rcv() can queue skb without checking
if skb is shared or not.

Many thanks to Ivaylo Dimitrov for his help, diagnosis and tests.

Reported-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Tested-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Remi Denis-Courmont <courmisch@...il.com>
---
 net/phonet/af_phonet.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/phonet/af_phonet.c b/net/phonet/af_phonet.c
index 10d42f3220ab..f925753668a7 100644
--- a/net/phonet/af_phonet.c
+++ b/net/phonet/af_phonet.c
@@ -377,6 +377,10 @@ static int phonet_rcv(struct sk_buff *skb, struct net_device *dev,
 	struct sockaddr_pn sa;
 	u16 len;
 
+	skb = skb_share_check(skb, GFP_ATOMIC);
+	if (!skb)
+		return NET_RX_DROP;
+
 	/* check we have at least a full Phonet header */
 	if (!pskb_pull(skb, sizeof(struct phonethdr)))
 		goto out;