[PATCH 3.2 189/221] ping: Fix race in free in receive path

[Ben Hutchings]

3.2.69-rc1 review patch.  If anyone has any objections, please let me know.

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

From: "subashab@xxxxxxxxxxxxxx" <subashab@xxxxxxxxxxxxxx>

[ Upstream commit fc752f1f43c1c038a2c6ae58cc739ebb5953ccb0 ]

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@xxxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/ipv4/ping.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -717,8 +717,11 @@ void ping_rcv(struct sk_buff *skb)
 	sk = ping_v4_lookup(net, saddr, daddr, ntohs(icmph->un.echo.id),
 			    skb->dev->ifindex);
 	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;
 	}

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