Re: [PATCH net-next] sctp: bring inet(6)_skb_parm back to sctp_input_cb

Marcelo Ricardo Leitner
2020-11-05T03:49:16Z

On Wed, Nov 04, 2020 at 02:55:32PM +0800, Xin Long wrote:
> inet(6)_skb_parm was removed from sctp_input_cb by Commit a1dd2cf2f1ae
> ("sctp: allow changing transport encap_port by peer packets"), as it
> thought sctp_input_cb->header is not used any more in SCTP.
>
> syzbot reported a crash:
>
> [ ] BUG: KASAN: use-after-free in decode_session6+0xe7c/0x1580
> [ ]
> [ ] Call Trace:
> [ ] <IRQ>
> [ ] dump_stack+0x107/0x163
> [ ] kasan_report.cold+0x1f/0x37
> [ ] decode_session6+0xe7c/0x1580
> [ ] __xfrm_policy_check+0x2fa/0x2850
> [ ] sctp_rcv+0x12b0/0x2e30
> [ ] sctp6_rcv+0x22/0x40
> [ ] ip6_protocol_deliver_rcu+0x2e8/0x1680
> [ ] ip6_input_finish+0x7f/0x160
> [ ] ip6_input+0x9c/0xd0
> [ ] ipv6_rcv+0x28e/0x3c0
>
> It was caused by sctp_input_cb->header/IP6CB(skb) still used in sctp rx
> path decode_session6() but some members overwritten by sctp6_rcv().
>
> This patch is to fix it by bring inet(6)_skb_parm back to sctp_input_cb
> and not overwriting it in sctp4/6_rcv() and sctp_udp_rcv().
>
> Reported-by: syzbot+5be8aebb1b7dfa90ef31@syzkaller.appspotmail.com
> Fixes: a1dd2cf2f1ae ("sctp: allow changing transport encap_port by peer packets")
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Thanks Xin.