Re: [PATCH 4.14 61/81] ALSA: seq: Protect in-kernel ioctl calls with mutex

[Takashi Iwai]

On Thu, 13 Jun 2019 10:33:44 +0200,
Greg Kroah-Hartman wrote:
> 
> [ Upstream commit feb689025fbb6f0aa6297d3ddf97de945ea4ad32 ]
> 
> ALSA OSS sequencer calls the ioctl function indirectly via
> snd_seq_kernel_client_ctl().  While we already applied the protection
> against races between the normal ioctls and writes via the client's
> ioctl_mutex, this code path was left untouched.  And this seems to be
> the cause of still remaining some rare UAF as spontaneously triggered
> by syzkaller.
> 
> For the sake of robustness, wrap the ioctl_mutex also for the call via
> snd_seq_kernel_client_ctl(), too.
> 
> Reported-by: syzbot+e4c8abb920efa77bace9@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

This commit is reverted later by commit f0654ba94e33.
So please drop this.  The proper fix is done later by commit
7c32ae35fbf9 ("ALSA: seq: Cover unsubscribe_port() in list_mutex")

Ditto for 4.19.y and 5.1.y.


thanks,

Takashi

> ---
>  sound/core/seq/seq_clientmgr.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
> index 3bcd7a2f0394..692631bd4a35 100644
> --- a/sound/core/seq/seq_clientmgr.c
> +++ b/sound/core/seq/seq_clientmgr.c
> @@ -2348,14 +2348,19 @@ int snd_seq_kernel_client_ctl(int clientid, unsigned int cmd, void *arg)
>  {
>  	const struct ioctl_handler *handler;
>  	struct snd_seq_client *client;
> +	int err;
>  
>  	client = clientptr(clientid);
>  	if (client == NULL)
>  		return -ENXIO;
>  
>  	for (handler = ioctl_handlers; handler->cmd > 0; ++handler) {
> -		if (handler->cmd == cmd)
> -			return handler->func(client, arg);
> +		if (handler->cmd == cmd) {
> +			mutex_lock(&client->ioctl_mutex);
> +			err = handler->func(client, arg);
> +			mutex_unlock(&client->ioctl_mutex);
> +			return err;
> +		}
>  	}
>  
>  	pr_debug("ALSA: seq unknown ioctl() 0x%x (type='%c', number=0x%02x)\n",
> -- 
> 2.20.1
> 
> 
>