ALSA: pcm: Fix UAF in snd_pcm_oss_get_formats() (01c0b426) · Commits · 戴 / test

snd_pcm_oss_get_formats() has an obvious use-after-free around snd_mask_test() calls, as spotted by syzbot. The passed format_mask argument is a pointer to the hw_params object that is freed before the loop. What a surprise that it has been present since the original code of decades ago... Reported-by:

<syzbot+4090700a4f13fccaf648@syzkaller.appspotmail.com> Cc: <stable@vger.kernel.org> Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/core/oss/pcm_oss.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -1762,10 +1762,9 @@ static int snd_pcm_oss_get_formats(struct snd_pcm_oss_file *pcm_oss_file)
		return -ENOMEM;
		_snd_pcm_hw_params_any(params);
		err = snd_pcm_hw_refine(substream, params);
		format_mask = hw_param_mask_c(params, SNDRV_PCM_HW_PARAM_FORMAT);
		kfree(params);
		if (err < 0)
		return err;
		goto error;
		format_mask = hw_param_mask_c(params, SNDRV_PCM_HW_PARAM_FORMAT);
		for (fmt = 0; fmt < 32; ++fmt) {
		if (snd_mask_test(format_mask, fmt)) {
		int f = snd_pcm_oss_format_to(fmt);
		@@ -1773,7 +1772,10 @@ static int snd_pcm_oss_get_formats(struct snd_pcm_oss_file *pcm_oss_file)
		formats \|= f;
		}
		}
		return formats;

		error:
		kfree(params);
		return err < 0 ? err : formats;
		}

		static int snd_pcm_oss_set_format(struct snd_pcm_oss_file *pcm_oss_file, int format)

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