3.2.72-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Tested-by: Brenden Blanco <bblanco@xxxxxxxxxxxx>
Reviewed-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
net/core/datagram.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -128,12 +128,12 @@ 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))
@@ -141,7 +141,7 @@ static int skb_set_peeked(struct sk_buff
nskb = skb_clone(skb, GFP_ATOMIC);
if (!nskb)
- return -ENOMEM;
+ return ERR_PTR(-ENOMEM);
skb->prev->next = nskb;
skb->next->prev = nskb;
@@ -154,7 +154,7 @@ static int skb_set_peeked(struct sk_buff
done:
skb->peeked = 1;
- return 0;
+ return skb;
}
/**
@@ -216,8 +216,9 @@ struct sk_buff *__skb_recv_datagram(stru
*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);
--
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