Patch "ALSA: control: Fix memory corruption risk in snd_ctl_elem_read" has been added to the 4.15-stable tree

[<gregkh@linuxfoundation.org>]

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

    ALSA: control: Fix memory corruption risk in snd_ctl_elem_read

to the 4.15-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-control-fix-memory-corruption-risk-in-snd_ctl_elem_read.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 5a23699a39abc5328921a81b89383d088f6ba9cc Mon Sep 17 00:00:00 2001
From: Richard Fitzgerald <rf@opensource.cirrus.com>
Date: Tue, 27 Feb 2018 17:01:18 +0000
Subject: ALSA: control: Fix memory corruption risk in snd_ctl_elem_read

From: Richard Fitzgerald <rf@opensource.cirrus.com>

commit 5a23699a39abc5328921a81b89383d088f6ba9cc upstream.

The patch "ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE
operations" introduced a potential for kernel memory corruption due
to an incorrect if statement allowing non-readable controls to fall
through and call the get function. For TLV controls a driver can omit
SNDRV_CTL_ELEM_ACCESS_READ to ensure that only the TLV get function
can be called. Instead the normal get() can be invoked unexpectedly
and as the driver expects that this will only be called for controls
<= 512 bytes, potentially try to copy >512 bytes into the 512 byte
return array, so corrupting kernel memory.

The problem is an attempt to refactor the snd_ctl_elem_read function
to invert the logic so that it conditionally aborted if the control
is unreadable instead of conditionally executing. But the if statement
wasn't inverted correctly.

The correct inversion of

    if (a && !b)

is
    if (!a || b)

Fixes: becf9e5d553c2 ("ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE operations")
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 sound/core/control.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -888,7 +888,7 @@ static int snd_ctl_elem_read(struct snd_
 
 	index_offset = snd_ctl_get_ioff(kctl, &control->id);
 	vd = &kctl->vd[index_offset];
-	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) && kctl->get == NULL)
+	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) || kctl->get == NULL)
 		return -EPERM;
 
 	snd_ctl_build_ioff(&control->id, kctl, index_offset);


Patches currently in stable-queue which might be from rf@opensource.cirrus.com are

queue-4.15/alsa-control-fix-memory-corruption-risk-in-snd_ctl_elem_read.patch