ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF

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.

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>

diff --git a/sound/core/control.c b/sound/core/control.c
index 50e7ba66f1876efd03e31e7cf1ab4d5ddcb4fb88..82aa1af1d1d873566fef0b188750e03995626aad 100644 (file)
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1203,14 +1203,19 @@ static int snd_ctl_elem_read(struct snd_card *card,
        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);
 
@@ -1220,7 +1225,7 @@ static int snd_ctl_elem_read(struct snd_card *card,
        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))
@@ -1230,7 +1235,7 @@ static int snd_ctl_elem_read(struct snd_card *card,
                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,
@@ -1238,8 +1243,11 @@ static int snd_ctl_elem_read(struct snd_card *card,
                        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;
 }
 
@@ -1253,9 +1261,7 @@ static int snd_ctl_elem_read_user(struct snd_card *card,
        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;