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>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f886531..ab66683 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1227,7 +1227,14 @@
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) {