ALSA: pcm: oss: Fix potential out-of-bounds shift (175b8d89) · Commits · 戴 / test

syzbot spotted a potential out-of-bounds shift in the PCM OSS layer where it calculates the buffer size with the arbitrary shift value given via an ioctl. Add a range check for avoiding the undefined behavior. As the value can be treated by a signed integer, the max shift should be 30. Reported-by:

<syzbot+df7dc146ebdd6435eea3@syzkaller.appspotmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20201209084552.17109-2-tiwai@suse.de Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/core/oss/pcm_oss.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -1935,11 +1935,15 @@ static int snd_pcm_oss_set_subdivide(struct snd_pcm_oss_file *pcm_oss_file, int
		static int snd_pcm_oss_set_fragment1(struct snd_pcm_substream *substream, unsigned int val)
		{
		struct snd_pcm_runtime *runtime;
		int fragshift;

		runtime = substream->runtime;
		if (runtime->oss.subdivision \|\| runtime->oss.fragshift)
		return -EINVAL;
		runtime->oss.fragshift = val & 0xffff;
		fragshift = val & 0xffff;
		if (fragshift >= 31)
		return -EINVAL;
		runtime->oss.fragshift = fragshift;
		runtime->oss.maxfrags = (val >> 16) & 0xffff;
		if (runtime->oss.fragshift < 4) /* < 16 */
		runtime->oss.fragshift = 4;

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