On Tue, Oct 17, 2017 at 09:44:10AM -0700, Eric Dumazet wrote:
> On Tue, Oct 17, 2017 at 9:28 AM, Marcelo Ricardo Leitner
> <marcelo.leitner@xxxxxxxxx> wrote:
> > On Tue, Oct 17, 2017 at 11:31:30PM +0800, Xin Long wrote:
> >> On Tue, Oct 17, 2017 at 9:45 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> >> > SCTP experts.
> >> >
> >> > syszkaller reported a few crashes in sctp_packet_config() with invalid
> >> > access to a deleted dst.
> >> >
> >> > The rcu_read_lock() in sctp_packet_config() is suspect.
> >> >
> >> > It does not protect anything at the moment.
> >> >
> >> > If we expect tp->dst to be manipulated/changed by another cpu/thread,
> >> > then we need proper rcu protection.
> >> >
> >> > Following patch to show what would be a minimal change (but obviously
> >> > bigger changes are needed, like sctp_transport_pmtu_check() and
> >> > sctp_transport_dst_check(), and proper sparse annotations)
> >> will check all places accessing tp->dst in sctp.
> >
> > I checked some and sctp_transport_dst_check() should be fine because
> > by then we are holding a reference on dst. Same goes to
> > sctp_transport_pmtu_check().
>
> Really ?
>
Yes,
> What about sctp_v4_err() -> sctp_icmp_redirect() -> sctp_transport_dst_check()
>
> It seems quite possible that the BH handler can access it, while
> socket is owned by user.
hidden here:
sctp_v4_err() {
...
sk = sctp_err_lookup(net, AF_INET, skb, sctp_hdr(skb), &asoc,
&transport);
...
out_unlock:
sctp_err_finish(sk, transport);
}
sctp_err_lookup() {
...
bh_lock_sock(sk);
/* If too many ICMPs get dropped on busy
* servers this needs to be solved differently.
*/
if (sock_owned_by_user(sk)) [A]
__NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS);
*app = asoc;
*tpp = transport;
return sk;
...
}
Though that if() on [A] should be bailing out without returning
nothing. That's a bug. More like:
if (sock_owned_by_user(sk)) {
__NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS);
goto out;
}
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