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 Tested-by: Zhen Chen Signed-off-by: Xin Long --- 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