On Wed, Nov 11, 2015, at 20:14, Hannes Frederic Sowa wrote: > On Wed, Nov 11, 2015, at 19:58, Eric Dumazet wrote: > > On Tue, 2015-11-10 at 16:23 +0100, Hannes Frederic Sowa wrote: > > > During splicing an af-unix socket to a pipe we have to drop all > > > af-unix socket locks. While doing so we allow another reader to enter > > > unix_stream_read_generic which can read, copy and finally free another > > > skb. If exactly this skb is just in process of being spliced we get a > > > use-after-free report by kasan. > > > > > > First, we must make sure to not have a free while the skb is used during > > > the splice operation. We simply increment its use counter before unlocking > > > the reader lock. > > > > > > Stream sockets have the nice characteristic that we don't care about > > > zero length writes and they never reach the peer socket's queue. That > > > said, we can take the UNIXCB.consumed field as the indicator if the > > > skb was already freed from the socket's receive queue. If the skb was > > > fully consumed after we locked the reader side again we know it has been > > > dropped by a second reader. We indicate a short read to user space and > > > abort the current splice operation. > > > > > > This bug has been found with syzkaller > > > (http://github.com/google/syzkaller) by Dmitry Vyukov. > > > > > > Fixes: 2b514574f7e8 ("net: af_unix: implement splice for stream af_unix > > > sockets") > > > Reported-by: Dmitry Vyukov <dvyu...@google.com> > > > Cc: Dmitry Vyukov <dvyu...@google.com> > > > Cc: Eric Dumazet <eric.duma...@gmail.com> > > > Acked-by: Eric Dumazet <eduma...@google.com> > > > Signed-off-by: Hannes Frederic Sowa <han...@stressinduktion.org> > > > --- > > > v2: add missing consume_skb in error path of recv_actor > > > v3: move skb_get to separate line as proposed by Eric Dumazet (thanks!) > > > > > > > I believe there is another bug in unix_stream_sendpage() > > > > skb = skb_peek_tail(&other->sk_receive_queue); > > if (tail && tail == skb) { > > > > Is clearly not safe ? > > Can you elaborate? > > I use tail as a cookie and check if we already tried to append to the > same tail skb with skb_append_pagefrags. If during allocation, which we > do outside of the locks, a new skb arrives, we take that and try to > append again (and free the old skb), to correctly not create any > reordering in the data stream. > > You think that tail could be reused in the meanwhile?
Also note, I never use the content of the tail pointer and we don't trim the skb from the end when it is still alive in the socket queue. Bye, Hannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
