On Mon, Jan 18, 2016 at 2:37 PM, Takashi Iwai tiwai@suse.de wrote:
On Mon, 18 Jan 2016 04:49:18 +0100, Nicolas Boichat wrote:
Running a kernel with KASan enabled, we spotted that the following read in sound/soc/soc-pcm.c:soc_pcm_hw_params() is out of bounds:
/* copy params for each codec */ codec_params = *params;The problem comes from sound/core/pcm_compat.c, snd_pcm_ioctl_hw_params_compat, where we're copying from a struct snd_pcm_hw_params to a struct snd_pcm_hw_params32:
/* only fifo_size is different, so just copy all */ data = memdup_user(data32, sizeof(*data32));It turns out that snd_pcm_hw_params is 4 bytes longer than snd_pcm_hw_params32, that's why an out-of-bounds read happens.
We separate kmalloc and memory copy operations to make sure data has the correct length.
Signed-off-by: Nicolas Boichat drinkcat@chromium.org
Thanks for reporting. This is indeed effectively a revert of the commit ef44a1ec6eee ('ALSA: sound/core: use memdup_user()'), which is obviously wrong. Sigh, it's a really danger of such a "cleanup" patch.
Oh, well spotted!
Could you rephrase the changelog mentioning the affecting commit and resubmit?
Sure. Looking at that commit, there is another suspicious memdup_user in sound/seq/seq_compat.c (similar issue: struct snd_seq_port_info32 is 4 bytes shorter than struct snd_seq_port_info). I'll revert that one as well.
Takashi
sound/core/pcm_compat.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c index b48b434..9630e9f 100644 --- a/sound/core/pcm_compat.c +++ b/sound/core/pcm_compat.c @@ -255,10 +255,15 @@ 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);-- 2.6.0.rc2.230.g3dd15c0