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Subject[PATCH 2.6.32 12/38] [PATCH 12/38] net: Fix skb_set_peeked use-after-free bug
2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

commit a0a2a6602496a45ae838a96db8b8173794b5d398 upstream.

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).

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: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit e553622ccb6b6e06079f980f55cf04128db3420c)
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
net/core/datagram.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index cbb3100..c855336 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -127,12 +127,12 @@ 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))
@@ -140,7 +140,7 @@ 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;
@@ -153,7 +153,7 @@ static int skb_set_peeked(struct sk_buff *skb)
done:
skb->peeked = 1;

- return 0;
+ return skb;
}

/**
@@ -214,8 +214,9 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned flags,
*peeked = skb->peeked;
if (flags & MSG_PEEK) {

- 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);
--
1.7.12.2.21.g234cd45.dirty




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