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Commit a0a2a660 authored by Herbert Xu's avatar Herbert Xu Committed by David S. Miller
Browse files

net: Fix skb_set_peeked use-after-free bug 



The commit 738ac1eb ("net: Clone
skb before setting peeked flag") introduced a use-after-free bug
in skb_recv_datagram.  This is because skb_set_peeked may create
a new skb and free the existing one.  As it stands the caller will
continue to use the old freed skb.

This patch fixes it by making skb_set_peeked return the new skb
(or the old one if unchanged).

Fixes: 738ac1eb ("net: Clone skb before setting peeked flag")
Reported-by: default avatarBrenden Blanco <bblanco@plumgrid.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Tested-by: default avatarBrenden Blanco <bblanco@plumgrid.com>
Reviewed-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 14d2b7c1

net/core/datagram.c

+7 −6
Original line number Diff line number Diff line
@@ -131,12 +131,12 @@ static int wait_for_more_packets(struct sock *sk, int *err, long *timeo_p, 
	goto out;

}



static int skb_set_peeked(struct sk_buff *skb)

static struct sk_buff *skb_set_peeked(struct sk_buff *skb)

{

	struct sk_buff *nskb;



	if (skb->peeked)

		return 0;

		return skb;



	/* We have to unshare an skb before modifying it. */

	if (!skb_shared(skb))
@@ -144,7 +144,7 @@ static int skb_set_peeked(struct sk_buff *skb) 


	nskb = skb_clone(skb, GFP_ATOMIC);

	if (!nskb)

		return -ENOMEM;

		return ERR_PTR(-ENOMEM);



	skb->prev->next = nskb;

	skb->next->prev = nskb;
@@ -157,7 +157,7 @@ static int skb_set_peeked(struct sk_buff *skb) 
done:

	skb->peeked = 1;



	return 0;

	return skb;

}



/**
@@ -229,8 +229,9 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags, 
					continue;

				}



				error = skb_set_peeked(skb);

				if (error)

				skb = skb_set_peeked(skb);

				error = PTR_ERR(skb);

				if (IS_ERR(skb))

					goto unlock_err;



				atomic_inc(&skb->users);