ALSA: core: Add async signal helpers

Currently the call of kill_fasync() from an interrupt handler might
lead to potential spin deadlocks, as spotted by syzkaller.
Unfortunately, it's not so trivial to fix this lock chain as it's
involved with the tasklist_lock that is touched in allover places.

As a temporary workaround, this patch provides the way to defer the
async signal notification in a work.  The new helper functions,
snd_fasync_helper() and snd_kill_faync() are replacements for
fasync_helper() and kill_fasync(), respectively.  In addition,
snd_fasync_free() needs to be called at the destructor of the relevant
file object.

Link: https://lore.kernel.org/r/20220728125945.29533-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2022-07-28 14:59:42 +02:00
parent 87eb04bb87
commit ef34a0ae7a
2 changed files with 102 additions and 0 deletions

View File

@ -507,4 +507,12 @@ snd_pci_quirk_lookup_id(u16 vendor, u16 device,
}
#endif
/* async signal helpers */
struct snd_fasync;
int snd_fasync_helper(int fd, struct file *file, int on,
struct snd_fasync **fasyncp);
void snd_kill_fasync(struct snd_fasync *fasync, int signal, int poll);
void snd_fasync_free(struct snd_fasync *fasync);
#endif /* __SOUND_CORE_H */

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@ -10,6 +10,7 @@
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/ioport.h>
#include <linux/fs.h>
#include <sound/core.h>
#ifdef CONFIG_SND_DEBUG
@ -145,3 +146,96 @@ snd_pci_quirk_lookup(struct pci_dev *pci, const struct snd_pci_quirk *list)
}
EXPORT_SYMBOL(snd_pci_quirk_lookup);
#endif
/*
* Deferred async signal helpers
*
* Below are a few helper functions to wrap the async signal handling
* in the deferred work. The main purpose is to avoid the messy deadlock
* around tasklist_lock and co at the kill_fasync() invocation.
* fasync_helper() and kill_fasync() are replaced with snd_fasync_helper()
* and snd_kill_fasync(), respectively. In addition, snd_fasync_free() has
* to be called at releasing the relevant file object.
*/
struct snd_fasync {
struct fasync_struct *fasync;
int signal;
int poll;
int on;
struct list_head list;
};
static DEFINE_SPINLOCK(snd_fasync_lock);
static LIST_HEAD(snd_fasync_list);
static void snd_fasync_work_fn(struct work_struct *work)
{
struct snd_fasync *fasync;
spin_lock_irq(&snd_fasync_lock);
while (!list_empty(&snd_fasync_list)) {
fasync = list_first_entry(&snd_fasync_list, struct snd_fasync, list);
list_del_init(&fasync->list);
spin_unlock_irq(&snd_fasync_lock);
if (fasync->on)
kill_fasync(&fasync->fasync, fasync->signal, fasync->poll);
spin_lock_irq(&snd_fasync_lock);
}
spin_unlock_irq(&snd_fasync_lock);
}
static DECLARE_WORK(snd_fasync_work, snd_fasync_work_fn);
int snd_fasync_helper(int fd, struct file *file, int on,
struct snd_fasync **fasyncp)
{
struct snd_fasync *fasync = NULL;
if (on) {
fasync = kzalloc(sizeof(*fasync), GFP_KERNEL);
if (!fasync)
return -ENOMEM;
INIT_LIST_HEAD(&fasync->list);
}
spin_lock_irq(&snd_fasync_lock);
if (*fasyncp) {
kfree(fasync);
fasync = *fasyncp;
} else {
if (!fasync) {
spin_unlock_irq(&snd_fasync_lock);
return 0;
}
*fasyncp = fasync;
}
fasync->on = on;
spin_unlock_irq(&snd_fasync_lock);
return fasync_helper(fd, file, on, &fasync->fasync);
}
EXPORT_SYMBOL_GPL(snd_fasync_helper);
void snd_kill_fasync(struct snd_fasync *fasync, int signal, int poll)
{
unsigned long flags;
if (!fasync || !fasync->on)
return;
spin_lock_irqsave(&snd_fasync_lock, flags);
fasync->signal = signal;
fasync->poll = poll;
list_move(&fasync->list, &snd_fasync_list);
schedule_work(&snd_fasync_work);
spin_unlock_irqrestore(&snd_fasync_lock, flags);
}
EXPORT_SYMBOL_GPL(snd_kill_fasync);
void snd_fasync_free(struct snd_fasync *fasync)
{
if (!fasync)
return;
fasync->on = 0;
flush_work(&snd_fasync_work);
kfree(fasync);
}
EXPORT_SYMBOL_GPL(snd_fasync_free);