[PATCH] ping: Fix race in free in receive path

[PATCH] ping: Fix race in free in receive path

[subashab]

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>
---
 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 c0d82f7..2a3720f 100644
--- 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;
 	}
-- 
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 a Linux Foundation Collaborative Project

Re: [PATCH] ping: Fix race in free in receive path

[Eric Dumazet]

On Fri, 2015-01-23 at 22:26 +0000, subashab@codeaurora.org wrote:
> 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().
...
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
> Cc: Eric Dumazet <edumazet@google.com>
> ---

Thanks !

Signed-off-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH] ping: Fix race in free in receive path

[David Miller]

From: subashab@codeaurora.org
Date: Fri, 23 Jan 2015 22:26:02 -0000

> 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>

Applied and queued up for -stable, thanks.