From 92b62b7416af11fcfaab7373b15a32a471500bab Mon Sep 17 00:00:00 2001 From: Maoyi Xie Date: Tue, 19 May 2026 03:40:23 +0800 Subject: [PATCH] ALSA: seq: avoid past-the-end iterator in snd_seq_create_port() snd_seq_create_port() walks client->ports_list_head looking for the ordered insertion point and on loop fall-through passes &p->list to list_add_tail(): list_for_each_entry(p, &client->ports_list_head, list) { if (p->addr.port == port) { kfree(new_port); return -EBUSY; } if (p->addr.port > num) break; ... } list_add_tail(&new_port->list, &p->list); When the loop walks all entries without break (e.g., the new port sorts last), p is past-the-end. &p->list aliases &client->ports_list_head (the list head) via container_of offset cancellation, so the insert lands at the list tail. That is the intended behaviour, but the access is undefined per C11 even though it works in practice. Track an explicit insert_before pointer initialised to the list head and overwritten to &p->list only when the loop breaks early. The observable behaviour is unchanged. Fixes: 9244b2c3079f ("[ALSA] alsa core: convert to list_for_each_entry*") Signed-off-by: Maoyi Xie Link: https://patch.msgid.link/20260518194023.1667857-3-maoyixie.tju@gmail.com Signed-off-by: Takashi Iwai --- sound/core/seq/seq_ports.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c index da8d358958f1..31ab4681c601 100644 --- a/sound/core/seq/seq_ports.c +++ b/sound/core/seq/seq_ports.c @@ -144,18 +144,21 @@ int snd_seq_create_port(struct snd_seq_client *client, int port, num = max(port, 0); guard(mutex)(&client->ports_mutex); guard(write_lock_irq)(&client->ports_lock); + struct list_head *insert_before = &client->ports_list_head; list_for_each_entry(p, &client->ports_list_head, list) { if (p->addr.port == port) { kfree(new_port); return -EBUSY; } - if (p->addr.port > num) + if (p->addr.port > num) { + insert_before = &p->list; break; + } if (port < 0) /* auto-probe mode */ num = p->addr.port + 1; } /* insert the new port */ - list_add_tail(&new_port->list, &p->list); + list_add_tail(&new_port->list, insert_before); client->num_ports++; new_port->addr.port = num; /* store the port number in the port */ sprintf(new_port->name, "port-%d", num);