ping: Fix race in free in receive path

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@codeaurora.org>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index c0d82f7..2a3720f 100644 (file)
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -966,8 +966,11 @@ bool 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 true;
        }