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af_unix: don't append consumed skbs to sk_receive_queue 

In case multiple writes to a unix stream socket race we could end up in a
situation where we pre-allocate a new skb for use in unix_stream_sendpage
but have to free it again in the locked section because another skb
has been appended meanwhile, which we must use. Accidentally we didn't
clear the pointer after consuming it and so we touched freed memory
while appending it to the sk_receive_queue. So, clear the pointer after
consuming the skb.

This bug has been found with syzkaller
(http://github.com/google/syzkaller) by Dmitry Vyukov.

Fixes: 869e7c6248 ("net: af_unix: implement stream sendpage support")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hannes Frederic Sowa 2015-11-16 16:25:56 +01:00 committed by David S. Miller
parent 24cb7055a3
commit 8844f97238
1 changed files with 1 additions and 0 deletions
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1
net/unix/af_unix.c
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@ -1800,6 +1800,7 @@ alloc_skb:
* this - does no harm
*/
consume_skb(newskb);
newskb = NULL;
}
if (skb_append_pagefrags(skb, page, offset, size)) {