linux-kernel - Re: [PATCH 5.1 043/115] ALSA: seq: Protect in-kernel ioctl calls with mutex

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Date:   Wed, 19 Jun 2019 14:16:38 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+e4c8abb920efa77bace9@...kaller.appspotmail.com,
        Takashi Iwai <tiwai@...e.de>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.1 043/115] ALSA: seq: Protect in-kernel ioctl calls
 with mutex

Hi!

> [ 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.

This is reverted with patch after the next one. Should simply this and
the revert be deleted from the queue?

Thanks,
								Pavel


> diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
> index 38e7deab6384..b3280e81bfd1 100644
> --- a/sound/core/seq/seq_clientmgr.c
> +++ b/sound/core/seq/seq_clientmgr.c
> @@ -2343,14 +2343,19 @@ 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",

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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