[3.19.y-ckt stable] Patch "net: Fix skb_set_peeked use-after-free bug" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Mon Sep 21 22:26:40 UTC 2015


This is a note to let you know that I have just added a patch titled

    net: Fix skb_set_peeked use-after-free bug

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt7.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From e3d2cda52ecf6bb28f80c2ac4abe274b471be03a Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert at gondor.apana.org.au>
Date: Tue, 4 Aug 2015 15:42:47 +0800
Subject: net: Fix skb_set_peeked use-after-free bug

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 at plumgrid.com>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Tested-by: Brenden Blanco <bblanco at plumgrid.com>
Reviewed-by: Konstantin Khlebnikov <khlebnikov at yandex-team.ru>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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 91dbcfa..f5cce20 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -131,12 +131,12 @@ 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))
@@ -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);
--
1.9.1





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