ALSA: rawmidi: Change resized buffers atomically

The SNDRV_RAWMIDI_IOCTL_PARAMS ioctl may resize the buffers and the
current code is racy.  For example, the sequencer client may write to
buffer while it being resized.

As a simple workaround, let's switch to the resized buffer inside the
stream runtime lock.

Reported-by: syzbot+52f83f0ea8df16932f7f@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index 69616d0..b53026a 100644 (file)
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -635,7 +635,7 @@ static int snd_rawmidi_info_select_user(struct snd_card *card,
 int snd_rawmidi_output_params(struct snd_rawmidi_substream *substream,
                              struct snd_rawmidi_params * params)
 {
-       char *newbuf;
+       char *newbuf, *oldbuf;
        struct snd_rawmidi_runtime *runtime = substream->runtime;
        
        if (substream->append && substream->use_count > 1)
@@ -648,13 +648,17 @@ int snd_rawmidi_output_params(struct snd_rawmidi_substream *substream,
                return -EINVAL;
        }
        if (params->buffer_size != runtime->buffer_size) {
-               newbuf = krealloc(runtime->buffer, params->buffer_size,
-                                 GFP_KERNEL);
+               newbuf = kmalloc(params->buffer_size, GFP_KERNEL);
                if (!newbuf)
                        return -ENOMEM;
+               spin_lock_irq(&runtime->lock);
+               oldbuf = runtime->buffer;
                runtime->buffer = newbuf;
                runtime->buffer_size = params->buffer_size;
                runtime->avail = runtime->buffer_size;
+               runtime->appl_ptr = runtime->hw_ptr = 0;
+               spin_unlock_irq(&runtime->lock);
+               kfree(oldbuf);
        }
        runtime->avail_min = params->avail_min;
        substream->active_sensing = !params->no_active_sensing;
@@ -665,7 +669,7 @@ EXPORT_SYMBOL(snd_rawmidi_output_params);
 int snd_rawmidi_input_params(struct snd_rawmidi_substream *substream,
                             struct snd_rawmidi_params * params)
 {
-       char *newbuf;
+       char *newbuf, *oldbuf;
        struct snd_rawmidi_runtime *runtime = substream->runtime;
 
        snd_rawmidi_drain_input(substream);
@@ -676,12 +680,16 @@ int snd_rawmidi_input_params(struct snd_rawmidi_substream *substream,
                return -EINVAL;
        }
        if (params->buffer_size != runtime->buffer_size) {
-               newbuf = krealloc(runtime->buffer, params->buffer_size,
-                                 GFP_KERNEL);
+               newbuf = kmalloc(params->buffer_size, GFP_KERNEL);
                if (!newbuf)
                        return -ENOMEM;
+               spin_lock_irq(&runtime->lock);
+               oldbuf = runtime->buffer;
                runtime->buffer = newbuf;
                runtime->buffer_size = params->buffer_size;
+               runtime->appl_ptr = runtime->hw_ptr = 0;
+               spin_unlock_irq(&runtime->lock);
+               kfree(oldbuf);
        }
        runtime->avail_min = params->avail_min;
        return 0;