[PATCH 6.18 034/227] sctp: move SCTP_CMD_ASSOC_SHKEY right after SCTP_CMD_PEER_INIT

Greg Kroah-Hartman
2026-01-28T15:53:51Z

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit a80c9d945aef55b23b54838334345f20251dad83 ]

A null-ptr-deref was reported in the SCTP transmit path when SCTP-AUTH key
initialization fails:

==================================================================
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 0 PID: 16 Comm: ksoftirqd/0 Tainted: G W 6.6.0 #2
RIP: 0010:sctp_packet_bundle_auth net/sctp/output.c:264 [inline]
RIP: 0010:sctp_packet_append_chunk+0xb36/0x1260 net/sctp/output.c:401
Call Trace:

sctp_packet_transmit_chunk+0x31/0x250 net/sctp/output.c:189
sctp_outq_flush_data+0xa29/0x26d0 net/sctp/outqueue.c:1111
sctp_outq_flush+0xc80/0x1240 net/sctp/outqueue.c:1217
sctp_cmd_interpreter.isra.0+0x19a5/0x62c0 net/sctp/sm_sideeffect.c:1787
sctp_side_effects net/sctp/sm_sideeffect.c:1198 [inline]
sctp_do_sm+0x1a3/0x670 net/sctp/sm_sideeffect.c:1169
sctp_assoc_bh_rcv+0x33e/0x640 net/sctp/associola.c:1052
sctp_inq_push+0x1dd/0x280 net/sctp/inqueue.c:88
sctp_rcv+0x11ae/0x3100 net/sctp/input.c:243
sctp6_rcv+0x3d/0x60 net/sctp/ipv6.c:1127

The issue is triggered when sctp_auth_asoc_init_active_key() fails in
sctp_sf_do_5_1C_ack() while processing an INIT_ACK. In this case, the
command sequence is currently:

- SCTP_CMD_PEER_INIT
- SCTP_CMD_TIMER_STOP (T1_INIT)
- SCTP_CMD_TIMER_START (T1_COOKIE)
- SCTP_CMD_NEW_STATE (COOKIE_ECHOED)
- SCTP_CMD_ASSOC_SHKEY
- SCTP_CMD_GEN_COOKIE_ECHO

If SCTP_CMD_ASSOC_SHKEY fails, asoc->shkey remains NULL, while
asoc->peer.auth_capable and asoc->peer.peer_chunks have already been set by
SCTP_CMD_PEER_INIT. This allows a DATA chunk with auth = 1 and shkey = NULL
to be queued by sctp_datamsg_from_user().

Since command interpretation stops on failure, no COOKIE_ECHO should been
sent via SCTP_CMD_GEN_COOKIE_ECHO. However, the T1_COOKIE timer has already
been started, and it may enqueue a COOKIE_ECHO into the outqueue later. As
a result, the DATA chunk can be transmitted together with the COOKIE_ECHO
in sctp_outq_flush_data(), leading to the observed issue.

Similar to the other places where it calls sctp_auth_asoc_init_active_key()
right after sctp_process_init(), this patch moves the SCTP_CMD_ASSOC_SHKEY
immediately after SCTP_CMD_PEER_INIT, before stopping T1_INIT and starting
T1_COOKIE. This ensures that if shared key generation fails, authenticated
DATA cannot be sent. It also allows the T1_INIT timer to retransmit INIT,
giving the client another chance to process INIT_ACK and retry key setup.

Fixes: 730fc3d05cd4 ("[SCTP]: Implete SCTP-AUTH parameter processing")
Reported-by: Zhen Chen <chenzhen126@huawei.com>
Tested-by: Zhen Chen <chenzhen126@huawei.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/44881224b375aa8853f5e19b4055a1a56d895813.1768324226.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sctp/sm_statefuns.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 3755ba079d077..7b823d7591419 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -603,6 +603,11 @@ enum sctp_disposition sctp_sf_do_5_1C_ack(struct net *net,
sctp_add_cmd_sf(commands, SCTP_CMD_PEER_INIT,
SCTP_PEER_INIT(initchunk));

+ /* SCTP-AUTH: generate the association shared keys so that
+ * we can potentially sign the COOKIE-ECHO.
+ */
+ sctp_add_cmd_sf(commands, SCTP_CMD_ASSOC_SHKEY, SCTP_NULL());
+
/* Reset init error count upon receipt of INIT-ACK. */
sctp_add_cmd_sf(commands, SCTP_CMD_INIT_COUNTER_RESET, SCTP_NULL());

@@ -617,11 +622,6 @@ enum sctp_disposition sctp_sf_do_5_1C_ack(struct net *net,
sctp_add_cmd_sf(commands, SCTP_CMD_NEW_STATE,
SCTP_STATE(SCTP_STATE_COOKIE_ECHOED));

- /* SCTP-AUTH: generate the association shared keys so that
- * we can potentially sign the COOKIE-ECHO.
- */
- sctp_add_cmd_sf(commands, SCTP_CMD_ASSOC_SHKEY, SCTP_NULL());
-
/* 5.1 C) "A" shall then send the State Cookie received in the
* INIT ACK chunk in a COOKIE ECHO chunk, ...
*/
--
2.51.0