6.9-stable review patch. If anyone has any objections, please let me know.
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From: Takashi Iwai tiwai@suse.de
commit 39381fe7394e5eafac76e7e9367e7351138a29c1 upstream.
The commit 81033c6b584b ("ALSA: core: Warn on empty module") introduced a WARN_ON() for a NULL module pointer passed at snd_card object creation, and it also wraps the code around it with '#ifdef MODULE'. This works in most cases, but the devils are always in details. "MODULE" is defined when the target code (i.e. the sound core) is built as a module; but this doesn't mean that the caller is also built-in or not. Namely, when only the sound core is built-in (CONFIG_SND=y) while the driver is a module (CONFIG_SND_USB_AUDIO=m), the passed module pointer is ignored even if it's non-NULL, and card->module remains as NULL. This would result in the missing module reference up/down at the device open/close, leading to a race with the code execution after the module removal.
For addressing the bug, move the assignment of card->module again out of ifdef. The WARN_ON() is still wrapped with ifdef because the module can be really NULL when all sound drivers are built-in.
Note that we keep 'ifdef MODULE' for WARN_ON(), otherwise it would lead to a false-positive NULL module check. Admittedly it won't catch perfectly, i.e. no check is performed when CONFIG_SND=y. But, it's no real problem as it's only for debugging, and the condition is pretty rare.
Fixes: 81033c6b584b ("ALSA: core: Warn on empty module") Reported-by: Xu Yang xu.yang_2@nxp.com Closes: https://lore.kernel.org/r/20240520170349.2417900-1-xu.yang_2@nxp.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de Tested-by: Xu Yang xu.yang_2@nxp.com Link: https://lore.kernel.org/r/20240522070442.17786-1-tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- sound/core/init.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/sound/core/init.c +++ b/sound/core/init.c @@ -313,8 +313,8 @@ static int snd_card_init(struct snd_card card->number = idx; #ifdef MODULE WARN_ON(!module); - card->module = module; #endif + card->module = module; INIT_LIST_HEAD(&card->devices); init_rwsem(&card->controls_rwsem); rwlock_init(&card->ctl_files_rwlock);