[PATCH net] sctp: move SCTP_CMD_ASSOC_SHKEY right after SCTP_CMD_PEER_INIT

[PATCH net] sctp: move SCTP_CMD_ASSOC_SHKEY right after SCTP_CMD_PEER_INIT

[Xin Long]

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>
---
 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 3755ba079d07..7b823d759141 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, ...
 	 */
-- 
2.47.1

Re: [PATCH net] sctp: move SCTP_CMD_ASSOC_SHKEY right after SCTP_CMD_PEER_INIT

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 13 Jan 2026 12:10:26 -0500 you wrote:
> 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:
> 
> [...]

Here is the summary with links:
  - [net] sctp: move SCTP_CMD_ASSOC_SHKEY right after SCTP_CMD_PEER_INIT
    https://git.kernel.org/netdev/net/c/a80c9d945aef

You are awesome, thank you!
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