The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From b3defb791b26ea0683a93a4f49c77ec45ec96f10 Mon Sep 17 00:00:00 2001
From: Takashi Iwai tiwai@suse.de Date: Tue, 9 Jan 2018 23:11:03 +0100 Subject: [PATCH] ALSA: seq: Make ioctls race-free
The ALSA sequencer ioctls have no protection against racy calls while the concurrent operations may lead to interfere with each other. As reported recently, for example, the concurrent calls of setting client pool with a combination of write calls may lead to either the unkillable dead-lock or UAF.
As a slightly big hammer solution, this patch introduces the mutex to make each ioctl exclusive. Although this may reduce performance via parallel ioctl calls, usually it's not demanded for sequencer usages, hence it should be negligible.
Reported-by: Luo Quan a4651386@163.com Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de
diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c index 6e22eea72654..d01913404581 100644 --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -221,6 +221,7 @@ static struct snd_seq_client *seq_create_client1(int client_index, int poolsize) rwlock_init(&client->ports_lock); mutex_init(&client->ports_mutex); INIT_LIST_HEAD(&client->ports_list_head); + mutex_init(&client->ioctl_mutex);
/* find free slot in the client table */ spin_lock_irqsave(&clients_lock, flags); @@ -2130,7 +2131,9 @@ static long snd_seq_ioctl(struct file *file, unsigned int cmd, return -EFAULT; }
+ mutex_lock(&client->ioctl_mutex); err = handler->func(client, &buf); + mutex_unlock(&client->ioctl_mutex); if (err >= 0) { /* Some commands includes a bug in 'dir' field. */ if (handler->cmd == SNDRV_SEQ_IOCTL_SET_QUEUE_CLIENT || diff --git a/sound/core/seq/seq_clientmgr.h b/sound/core/seq/seq_clientmgr.h index c6614254ef8a..0611e1e0ed5b 100644 --- a/sound/core/seq/seq_clientmgr.h +++ b/sound/core/seq/seq_clientmgr.h @@ -61,6 +61,7 @@ struct snd_seq_client { struct list_head ports_list_head; rwlock_t ports_lock; struct mutex ports_mutex; + struct mutex ioctl_mutex; int convert32; /* convert 32->64bit */
/* output pool */