The ALSA proc helper manages the child nodes in a linked list, but its addition and deletion is done without any lock. This leads to a corruption if they are operated concurrently. Usually this isn't a problem because the proc entries are added sequentially in the driver probe procedure itself. But the card registrations are done often asynchronously, and the crash could be actually reproduced with syzkaller.
This patch papers over it by protecting the link addition and deletion with the parent's mutex. There is "access" mutex that is used for the file access, and this can be reused for this purpose as well.
Reported-by: syzbot+48df349490c36f9f54ab@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/core/info.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/sound/core/info.c b/sound/core/info.c index 96a074019c33..0eb169acc850 100644 --- a/sound/core/info.c +++ b/sound/core/info.c @@ -713,8 +713,11 @@ snd_info_create_entry(const char *name, struct snd_info_entry *parent, INIT_LIST_HEAD(&entry->list); entry->parent = parent; entry->module = module; - if (parent) + if (parent) { + mutex_lock(&parent->access); list_add_tail(&entry->list, &parent->children); + mutex_unlock(&parent->access); + } return entry; }
@@ -792,7 +795,12 @@ void snd_info_free_entry(struct snd_info_entry * entry) list_for_each_entry_safe(p, n, &entry->children, list) snd_info_free_entry(p);
- list_del(&entry->list); + p = entry->parent; + if (p) { + mutex_lock(&p->access); + list_del(&entry->list); + mutex_unlock(&p->access); + } kfree(entry->name); if (entry->private_free) entry->private_free(entry);