On Thu, Nov 29, 2018 at 02:44:07PM +0800, Xin Long wrote:
> Without holding transport to dereference its asoc, a use after
> free panic can be caused in sctp_epaddr_lookup_transport. Note
> that a sock lock can't protect these transports that belong to
> other socks.
>
> A similar fix as Commit bab1be79a516 ("sctp: hold transport
> before accessing its asoc in sctp_transport_get_next") is
> needed to hold the transport before accessing its asoc in
> sctp_epaddr_lookup_transport.
>
> Note that this extra atomic operation is on the datapath,
> but as rhlist keeps the lists to a small size, it won't
> see a noticeable performance hurt.
>
> v1->v2:
> - improve the changelog.
>
> Fixes: 7fda702f9315 ("sctp: use new rhlist interface on sctp transport rhashtable")
> Reported-by: syzbot+aad231d51b1923158444@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> ---
> net/sctp/input.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index 5c36a99..ce7351c 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -967,9 +967,15 @@ struct sctp_transport *sctp_epaddr_lookup_transport(
> list = rhltable_lookup(&sctp_transport_hashtable, &arg,
> sctp_hash_params);
>
> - rhl_for_each_entry_rcu(t, tmp, list, node)
> - if (ep == t->asoc->ep)
> + rhl_for_each_entry_rcu(t, tmp, list, node) {
> + if (!sctp_transport_hold(t))
> + continue;
> + if (ep == t->asoc->ep) {
> + sctp_transport_put(t);
> return t;
> + }
> + sctp_transport_put(t);
> + }
>
> return NULL;
> }
> --
> 2.1.0
>
