netdev - [PATCH net 1/3] sctp: do asoc update earlier in sctp_sf_do_dupcook

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Date:   Sat,  1 May 2021 02:15:55 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        jere.leppanen@...ia.com,
        Alexander Sverdlin <alexander.sverdlin@...ia.com>
Subject: [PATCH net 1/3] sctp: do asoc update earlier in sctp_sf_do_dupcook_a

There's a panic that occurs in a few of envs, the call trace is as below:

  [] general protection fault, ... 0x29acd70f1000a: 0000 [#1] SMP PTI
  [] RIP: 0010:sctp_ulpevent_notify_peer_addr_change+0x4b/0x1fa [sctp]
  []  sctp_assoc_control_transport+0x1b9/0x210 [sctp]
  []  sctp_do_8_2_transport_strike.isra.16+0x15c/0x220 [sctp]
  []  sctp_cmd_interpreter.isra.21+0x1231/0x1a10 [sctp]
  []  sctp_do_sm+0xc3/0x2a0 [sctp]
  []  sctp_generate_timeout_event+0x81/0xf0 [sctp]

This is caused by a transport use-after-free issue. When processing a
duplicate COOKIE-ECHO chunk in sctp_sf_do_dupcook_a(), both COOKIE-ACK
and SHUTDOWN chunks are allocated with the transort from the new asoc.
However, later in the sideeffect machine, the old asoc is used to send
them out and old asoc's shutdown_last_sent_to is set to the transport
that SHUTDOWN chunk attached to in sctp_cmd_setup_t2(), which actually
belongs to the new asoc. After the new_asoc is freed and the old asoc
T2 timeout, the old asoc's shutdown_last_sent_to that is already freed
would be accessed in sctp_sf_t2_timer_expire().

Thanks Alexander and Jere for helping dig into this issue.

To fix it, this patch is to do the asoc update first, then allocate
the COOKIE-ACK and SHUTDOWN chunks with the 'updated' old asoc. This
would make more sense, as a chunk from an asoc shouldn't be sent out
with another asoc. We had fixed quite a few issues caused by this.

Fixes: 145cb2f7177d ("sctp: Fix bundling of SHUTDOWN with COOKIE-ACK")
Reported-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>
Reported-by: syzbot+bbe538efd1046586f587@...kaller.appspotmail.com
Reported-by: Michal Tesar <mtesar@...hat.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/sctp/sm_statefuns.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 7632714..30cb946 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -1852,20 +1852,35 @@ static enum sctp_disposition sctp_sf_do_dupcook_a(
 			SCTP_TO(SCTP_EVENT_TIMEOUT_T4_RTO));
 	sctp_add_cmd_sf(commands, SCTP_CMD_PURGE_ASCONF_QUEUE, SCTP_NULL());
 
-	repl = sctp_make_cookie_ack(new_asoc, chunk);
+	/* Update the content of current association. */
+	if (sctp_assoc_update((struct sctp_association *)asoc, new_asoc)) {
+		struct sctp_chunk *abort;
+
+		abort = sctp_make_abort(asoc, NULL, sizeof(struct sctp_errhdr));
+		if (abort) {
+			sctp_init_cause(abort, SCTP_ERROR_RSRC_LOW, 0);
+			sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
+		}
+		sctp_add_cmd_sf(commands, SCTP_CMD_SET_SK_ERR, SCTP_ERROR(ECONNABORTED));
+		sctp_add_cmd_sf(commands, SCTP_CMD_ASSOC_FAILED,
+				SCTP_PERR(SCTP_ERROR_RSRC_LOW));
+		SCTP_INC_STATS(net, SCTP_MIB_ABORTEDS);
+		SCTP_DEC_STATS(net, SCTP_MIB_CURRESTAB);
+		goto nomem;
+	}
+
+	repl = sctp_make_cookie_ack(asoc, chunk);
 	if (!repl)
 		goto nomem;
 
 	/* Report association restart to upper layer. */
 	ev = sctp_ulpevent_make_assoc_change(asoc, 0, SCTP_RESTART, 0,
-					     new_asoc->c.sinit_num_ostreams,
-					     new_asoc->c.sinit_max_instreams,
+					     asoc->c.sinit_num_ostreams,
+					     asoc->c.sinit_max_instreams,
 					     NULL, GFP_ATOMIC);
 	if (!ev)
 		goto nomem_ev;
 
-	/* Update the content of current association. */
-	sctp_add_cmd_sf(commands, SCTP_CMD_UPDATE_ASSOC, SCTP_ASOC(new_asoc));
 	sctp_add_cmd_sf(commands, SCTP_CMD_EVENT_ULP, SCTP_ULPEVENT(ev));
 	if ((sctp_state(asoc, SHUTDOWN_PENDING) ||
 	     sctp_state(asoc, SHUTDOWN_SENT)) &&
-- 
2.1.0