9bef081.diff

From 9bef081cc296e8448057a83221bcb263d4622c64 Mon Sep 17 00:00:00 2001
From: Clement Lecigne <clecigne@google.com>
Date: Fri, 13 Jan 2023 13:07:45 +0100
Subject: [PATCH] UPSTREAM: ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF

commit 56b88b50565cd8b946a2d00b0c83927b7ebb055e upstream.

Takes rwsem lock inside snd_ctl_elem_read instead of snd_ctl_elem_read_user
like it was done for write in commit 1fa4445f9adf1 ("ALSA: control - introduce
snd_ctl_notify_one() helper"). Doing this way we are also fixing the following
locking issue happening in the compat path which can be easily triggered and
turned into an use-after-free.

64-bits:
snd_ctl_ioctl
  snd_ctl_elem_read_user
    [takes controls_rwsem]
    snd_ctl_elem_read [lock properly held, all good]
    [drops controls_rwsem]

32-bits:
snd_ctl_ioctl_compat
  snd_ctl_elem_write_read_compat
    ctl_elem_write_read
      snd_ctl_elem_read [missing lock, not good]

CVE-2023-0266 was assigned for this issue.

Bug: 265303544
Cc: stable@kernel.org # 5.13+
Signed-off-by: Clement Lecigne <clecigne@google.com>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230113120745.25464-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: Ib0e85251a8fe47a52706fa5aaa2ea034370979fe
---

diff --git a/sound/core/control.c b/sound/core/control.c
index 6a8fd993..3ef27b4 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1177,14 +1177,19 @@
 	const u32 pattern = 0xdeadbeef;
 	int ret;
 
+	down_read(&card->controls_rwsem);
 	kctl = snd_ctl_find_id(card, &control->id);
-	if (kctl == NULL)
-		return -ENOENT;
+	if (kctl == NULL) {
+		ret = -ENOENT;
+		goto unlock;
+	}
 
 	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)
-		return -EPERM;
+	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) || kctl->get == NULL) {
+		ret = -EPERM;
+		goto unlock;
+	}
 
 	snd_ctl_build_ioff(&control->id, kctl, index_offset);
 
@@ -1194,7 +1199,7 @@
 	info.id = control->id;
 	ret = __snd_ctl_elem_info(card, kctl, &info, NULL);
 	if (ret < 0)
-		return ret;
+		goto unlock;
 #endif
 
 	if (!snd_ctl_skip_validation(&info))
@@ -1204,7 +1209,7 @@
 		ret = kctl->get(kctl, control);
 	snd_power_unref(card);
 	if (ret < 0)
-		return ret;
+		goto unlock;
 	if (!snd_ctl_skip_validation(&info) &&
 	    sanity_check_elem_value(card, control, &info, pattern) < 0) {
 		dev_err(card->dev,
@@ -1212,8 +1217,11 @@
 			control->id.iface, control->id.device,
 			control->id.subdevice, control->id.name,
 			control->id.index);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto unlock;
 	}
+unlock:
+	up_read(&card->controls_rwsem);
 	return ret;
 }
 
@@ -1227,9 +1235,7 @@
 	if (IS_ERR(control))
 		return PTR_ERR(control);
 
-	down_read(&card->controls_rwsem);
 	result = snd_ctl_elem_read(card, control);
-	up_read(&card->controls_rwsem);
 	if (result < 0)
 		goto error;