linux-kernel - [PATCH 3.16.y-ckt 30/58] ping: Fix race in free in receive path

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Message-Id: <1424353948-31863-31-git-send-email-luis.henriques@canonical.com>
Date:	Thu, 19 Feb 2015 13:52:00 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 30/58] ping: Fix race in free in receive path

3.16.7-ckt7 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "subashab@...eaurora.org" <subashab@...eaurora.org>

commit fc752f1f43c1c038a2c6ae58cc739ebb5953ccb0 upstream.

An exception is seen in ICMP ping receive path where the skb
destructor sock_rfree() tries to access a freed socket. This happens
because ping_rcv() releases socket reference with sock_put() and this
internally frees up the socket. Later icmp_rcv() will try to free the
skb and as part of this, skb destructor is called and which leads
to a kernel panic as the socket is freed already in ping_rcv().

-->|exception
-007|sk_mem_uncharge
-007|sock_rfree
-008|skb_release_head_state
-009|skb_release_all
-009|__kfree_skb
-010|kfree_skb
-011|icmp_rcv
-012|ip_local_deliver_finish

Fix this incorrect free by cloning this skb and processing this cloned
skb instead.

This patch was suggested by Eric Dumazet

Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Cc: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 net/ipv4/ping.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 620e8ffa62e8..7dec0787b4a2 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -973,8 +973,11 @@ void ping_rcv(struct sk_buff *skb)
 
 	sk = ping_lookup(net, skb, ntohs(icmph->un.echo.id));
 	if (sk != NULL) {
+		struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
+
 		pr_debug("rcv on socket %p\n", sk);
-		ping_queue_rcv_skb(sk, skb_get(skb));
+		if (skb2)
+			ping_queue_rcv_skb(sk, skb2);
 		sock_put(sk);
 		return;
 	}
-- 
2.1.4

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