Commit 85c4f2cf authored Aug 04, 2015 by Herbert Xu Committed by Ravinder Konka Feb 16, 2016

net: Fix skb_set_peeked use-after-free bug



[ Upstream commit a0a2a6602496a45ae838a96db8b8173794b5d398 ]

The commit 738ac1ebb96d02e0d23bc320302a6ea94c612dec ("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).

Change-Id: I5b4b543caef8640987876f6ab5a87a9dd1b42524
Fixes: 738ac1ebb96d ("net: Clone skb before setting peeked flag")
Reported-by: Brenden Blanco <bblanco@plumgrid.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Brenden Blanco <bblanco@plumgrid.com>
Reviewed-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: e308dd584ec309635129444e41dd4c90abf61842
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Ravinder Konka <rkonka@codeaurora.org>

parent 9de04e6b

net/core/datagram.c

+7 −6

Original line number	Diff line number	Diff line
		@@ -130,12 +130,12 @@ out_noerr:
		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))
		@@ -143,7 +143,7 @@ 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;
		@@ -156,7 +156,7 @@ static int skb_set_peeked(struct sk_buff *skb)
		done:
		skb->peeked = 1;

		return 0;
		return skb;
		}

		/**
		@@ -228,8 +228,9 @@ 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);