Patch "ALSA: pcm: Fix UAF in snd_pcm_oss_get_formats()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ALSA: pcm: Fix UAF in snd_pcm_oss_get_formats()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alsa-pcm-fix-uaf-in-snd_pcm_oss_get_formats.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Takashi Iwai <[email protected]>
Date: Sat, 10 Mar 2018 23:04:23 +0100
Subject: ALSA: pcm: Fix UAF in snd_pcm_oss_get_formats()

From: Takashi Iwai <[email protected]>

commit 01c0b4265cc16bc1f43f475c5944c55c10d5768f upstream.

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...

---
 sound/core/oss/pcm_oss.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

@@ -1814,10 +1814,9 @@ static int snd_pcm_oss_get_formats(struc
 		return -ENOMEM;
 	_snd_pcm_hw_params_any(params);
 	err = snd_pcm_hw_refine(substream, params);
-	format_mask = *hw_param_mask(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);

@@ -1825,7 +1824,10 @@ static int snd_pcm_oss_get_formats(struc
 				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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/alsa-firewire-digi00x-handle-all-midi-messages-on-streaming-packets.patch queue-4.4/alsa-pcm-fix-uaf-in-snd_pcm_oss_get_formats.patch queue-4.4/alsa-seq-fix-possible-uaf-in-snd_seq_check_queue.patch queue-4.4/alsa-hda-revert-power_save-option-default-value.patch queue-4.4/alsa-seq-clear-client-entry-before-deleting-else-at-closing.patch