sctp_sendmsg_to_asoc() selects a transport before waiting for a new interleaved association to become established. sctp_wait_for_connect() drops the socket lock while sleeping. While the lock is dropped, backlog processing can handle a COOKIE ACK and an ASCONF DEL-IP that removes the selected transport. sctp_assoc_rm_peer() then marks the transport dead and drops its association-owned reference. The transport can be freed through RCU before the send path resumes. After the wait, the stale pointer is assigned to newly created DATA or I-DATA chunks and later dereferenced by sctp_outq_select_transport(). Hold a reference to the selected transport across sctp_wait_for_connect(). After the socket lock is reacquired, abort the send if the transport was marked dead. Callers without a selected transport pass NULL and retain their existing behavior. Cc: stable@vger.kernel.org Fixes: 668c9beb9020 ("sctp: implement assign_number for sctp_stream_interleave") Acked-by: Xin Long Assisted-by: LLM Signed-off-by: Seung Min Shin --- Notes (sctp-connect-wait-v2): v2: - Rebase onto current net/main after commit 4f1da630d13de. - Preserve the RCV_SHUTDOWN check added by that commit. - Add the stable list now that the issue is public. v1: https://lore.kernel.org/netdev/20260928152132.3705137-1-guncraft2000@naver.com/ Tested on net/main af32da41b032 with CONFIG_KASAN=y on x86-64. Before the patch, the reproducer triggered a KASAN slab-use-after-free in sctp_outq_select_transport() on its first run. After the patch, 64 attempts completed without a KASAN, refcount, BUG, WARNING, oops, or panic report. A diagnostic run returned ESRCH in all 64 attempts and left the association in SCTP_ESTABLISHED state. A normal interleaved connect/send smoke test passed. net/sctp/socket.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) diff --git a/net/sctp/socket.c b/net/sctp/socket.c index e35692dd8d30..189b89a40d46 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c @@ -75,7 +75,8 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, struct sctp_transport *transport, long *timeo_p, size_t msg_len); static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p); -static int sctp_wait_for_connect(struct sctp_association *, long *timeo_p); +static int sctp_wait_for_connect(struct sctp_association *, + struct sctp_transport *, long *timeo_p); static int sctp_wait_for_accept(struct sock *sk, long timeo); static void sctp_wait_for_close(struct sock *sk, long timeo); static void sctp_destruct_sock(struct sock *sk); @@ -1245,7 +1246,7 @@ static int __sctp_connect(struct sock *sk, struct sockaddr *kaddrs, *assoc_id = asoc->assoc_id; timeo = sock_sndtimeo(sk, flags & O_NONBLOCK); - return sctp_wait_for_connect(asoc, &timeo); + return sctp_wait_for_connect(asoc, NULL, &timeo); out_free: pr_debug("%s: took out_free path with asoc:%p kaddrs:%p err:%d\n", @@ -1843,7 +1844,7 @@ static int sctp_sendmsg_to_asoc(struct sctp_association *asoc, if (asoc->ep->intl_enable) { timeo = sock_sndtimeo(sk, 0); - err = sctp_wait_for_connect(asoc, &timeo); + err = sctp_wait_for_connect(asoc, transport, &timeo); if (err || sk->sk_shutdown & RCV_SHUTDOWN) { err = -ESRCH; goto err; @@ -1881,7 +1882,7 @@ static int sctp_sendmsg_to_asoc(struct sctp_association *asoc, if (unlikely(wait_connect)) { timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT); - sctp_wait_for_connect(asoc, &timeo); + sctp_wait_for_connect(asoc, NULL, &timeo); } err = msg_len; @@ -9381,7 +9382,9 @@ static bool sctp_writeable(const struct sock *sk) /* Wait for an association to go into ESTABLISHED state. If timeout is 0, * returns immediately with EINPROGRESS. */ -static int sctp_wait_for_connect(struct sctp_association *asoc, long *timeo_p) +static int sctp_wait_for_connect(struct sctp_association *asoc, + struct sctp_transport *transport, + long *timeo_p) { struct sock *sk = asoc->base.sk; int err = 0; @@ -9390,12 +9393,16 @@ static int sctp_wait_for_connect(struct sctp_association *asoc, long *timeo_p) pr_debug("%s: asoc:%p, timeo:%ld\n", __func__, asoc, *timeo_p); - /* Increment the association's refcnt. */ + /* Hold references while the socket lock is dropped. */ + if (transport) + sctp_transport_hold(transport); sctp_association_hold(asoc); for (;;) { prepare_to_wait_exclusive(&asoc->wait, &wait, TASK_INTERRUPTIBLE); + if (transport && transport->dead) + goto do_transport_dead; if (!*timeo_p) goto do_nonblock; if (sk->sk_shutdown & RCV_SHUTDOWN) @@ -9424,7 +9431,8 @@ static int sctp_wait_for_connect(struct sctp_association *asoc, long *timeo_p) out: finish_wait(&asoc->wait, &wait); - /* Release the association's refcnt. */ + if (transport) + sctp_transport_put(transport); sctp_association_put(asoc); return err; @@ -9443,6 +9451,10 @@ static int sctp_wait_for_connect(struct sctp_association *asoc, long *timeo_p) do_nonblock: err = -EINPROGRESS; goto out; + +do_transport_dead: + err = -EAGAIN; + goto out; } static int sctp_wait_for_accept(struct sock *sk, long timeo) base-commit: af32da41b0327b9c6a37856ba82b6760d6c8d10e -- 2.34.1