From 8c2f870890fd28e023b0fcf49dcee333f2c8bad7 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Tue, 16 Apr 2019 15:25:00 +0200 Subject: [PATCH] ALSA: info: Fix racy addition/deletion of nodes 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: Signed-off-by: Takashi Iwai --- 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);