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tcp: Fix for race due to temporary drop of the socket lock in skb_splice_bits. 

skb_splice_bits temporary drops the socket lock while iterating over
the socket queue in order to break a reverse locking condition which
happens with sendfile. This, however, opens a window of opportunity
for tcp_collapse() to aggregate skbs and thus potentially free the
current skb used in skb_splice_bits and tcp_read_sock.

This patch fixes the problem by (re-)getting the same "logical skb"
after the lock has been temporary dropped.

Based on idea and initial patch from Evgeniy Polyakov.

Signed-off-by: Octavian Purdila <opurdila@ixiacom.com>
Acked-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Octavian Purdila 2008-06-04 15:45:58 -07:00 committed by David S. Miller
parent 26af65cbeb
commit 293ad60401
2 changed files with 11 additions and 3 deletions
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5
net/core/skbuff.c
View File

@ -1445,6 +1445,7 @@ done:
if (spd.nr_pages) {
int ret;
struct sock *sk = __skb->sk;
/*
* Drop the socket lock, otherwise we have reverse
@ -1455,9 +1456,9 @@ done:
* we call into ->sendpage() with the i_mutex lock held
* and networking will grab the socket lock.
*/
release_sock(__skb->sk);
release_sock(sk);
ret = splice_to_pipe(pipe, &spd);
lock_sock(__skb->sk);
lock_sock(sk);
return ret;
}

9
net/ipv4/tcp.c
View File

@ -1227,7 +1227,14 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
copied += used;
offset += used;
}
if (offset != skb->len)
/*
* If recv_actor drops the lock (e.g. TCP splice
* receive) the skb pointer might be invalid when
* getting here: tcp_collapse might have deleted it
* while aggregating skbs from the socket queue.
*/
skb = tcp_recv_skb(sk, seq-1, &offset);
if (!skb || (offset+1 != skb->len))
break;
}
if (tcp_hdr(skb)->fin) {