ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

commit 43c54b8c7cfe22f868a751ba8a59abf1724160b1 upstream.

This reverts one hunk of
commit ef44a1ec6eee ("ALSA: sound/core: use memdup_user()"), which
replaced a number of kmalloc followed by memcpy with memdup calls.

In this case, we are copying from a struct snd_pcm_hw_params32 to
a struct snd_pcm_hw_params, but the latter is 4 bytes longer than
the 32-bit version, so we need to separate kmalloc and copy calls.

This actually leads to an out-of-bounds memory access later on
in sound/soc/soc-pcm.c:soc_pcm_hw_params() (detected using KASan).

Fixes: ef44a1ec6eee ('ALSA: sound/core: use memdup_user()')
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index 4dbb66e..ceada09 100644 (file)
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -235,10 +235,15 @@ static int snd_pcm_ioctl_hw_params_compat(struct snd_pcm_substream *substream,
        if (! (runtime = substream->runtime))
                return -ENOTTY;
 
-       /* only fifo_size is different, so just copy all */
-       data = memdup_user(data32, sizeof(*data32));
-       if (IS_ERR(data))
-               return PTR_ERR(data);
+       data = kmalloc(sizeof(*data), GFP_KERNEL);
+       if (!data)
+               return -ENOMEM;
+
+       /* only fifo_size (RO from userspace) is different, so just copy all */
+       if (copy_from_user(data, data32, sizeof(*data32))) {
+               err = -EFAULT;
+               goto error;
+       }
 
        if (refine)
                err = snd_pcm_hw_refine(substream, data);