From dbd9d1cbf9700528c8595ab1fa7ef832e79821fe Mon Sep 17 00:00:00 2001 From: Nguyen Ngoc Thang Date: Tue, 15 Sep 2026 23:31:10 +0700 Subject: ALSA: usb-audio: fix list_add double-add in push_back_to_ready_list stop_urbs() clears ep->ready_playback_urbs with a bare INIT_LIST_HEAD() instead of unlinking each queued snd_urb_ctx. If a URB survives past wait_clear_urbs()'s forced STOPPING->STOPPED timeout, its ctx is left looking "linked" (stale next/prev) even though the list head has forgotten it. When the endpoint later restarts and re-queues that same ctx onto the (now real) ready list, and the old URB's completion handler then calls push_back_to_ready_list() for it a second time, the ctx is still the list's own tail and list_add's double-add check trips: kernel BUG at lib/list_debug.c:35 (list_add double add) Guard push_back_to_ready_list() with a list_empty() check so a still-linked ctx isn't re-added, and make stop_urbs() actually unlink each ctx via list_del_init() instead of only resetting the head, so a dropped ctx doesn't keep looking linked to that guard. Reported-by: syzbot+9fe3b8d9f5c64ff410a7@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9fe3b8d9f5c64ff410a7 Signed-off-by: Nguyen Ngoc Thang Link: https://patch.msgid.link/20260915163110.58124-1-ngocthang2710.1999@gmail.com Signed-off-by: Takashi Iwai --- sound/usb/endpoint.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c index b72ce1e9bfb1..879d0451536e 100644 --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -449,7 +449,9 @@ static void push_back_to_ready_list(struct snd_usb_endpoint *ep, struct snd_urb_ctx *ctx) { guard(spinlock_irqsave)(&ep->lock); - list_add_tail(&ctx->ready_list, &ep->ready_playback_urbs); + /* ctx may still be linked: a stale completion racing a stop/restart. */ + if (list_empty(&ctx->ready_list)) + list_add_tail(&ctx->ready_list, &ep->ready_playback_urbs); } /* @@ -1037,6 +1039,7 @@ void snd_usb_endpoint_sync_pending_stop(struct snd_usb_endpoint *ep) */ static int stop_urbs(struct snd_usb_endpoint *ep, bool force, bool keep_pending) { + struct snd_urb_ctx *ctx, *n; unsigned int i; if (!force && atomic_read(&ep->running)) @@ -1046,7 +1049,9 @@ static int stop_urbs(struct snd_usb_endpoint *ep, bool force, bool keep_pending) return 0; scoped_guard(spinlock_irqsave, &ep->lock) { - INIT_LIST_HEAD(&ep->ready_playback_urbs); + /* Unlink each ctx; INIT_LIST_HEAD() alone would leave them looking linked. */ + list_for_each_entry_safe(ctx, n, &ep->ready_playback_urbs, ready_list) + list_del_init(&ctx->ready_list); ep->next_packet_head = 0; ep->next_packet_queued = 0; } -- cgit v1.2.3