diff options
author | Takashi Iwai <tiwai@suse.de> | 2018-11-22 14:36:17 +0100 |
---|---|---|
committer | Takashi Iwai <tiwai@suse.de> | 2018-11-24 19:57:51 +0100 |
commit | e1a7bfe3807974e66f971f2589d4e0197ec0fced (patch) | |
tree | 2b2d423f63b366ea45d9ac665078361b6a3096cb | |
parent | 9a20332ab373b1f8f947e0a9c923652b32dab031 (diff) |
ALSA: control: Fix race between adding and removing a user element
The procedure for adding a user control element has some window opened
for race against the concurrent removal of a user element. This was
caught by syzkaller, hitting a KASAN use-after-free error.
This patch addresses the bug by wrapping the whole procedure to add a
user control element with the card->controls_rwsem, instead of only
around the increment of card->user_ctl_count.
This required a slight code refactoring, too. The function
snd_ctl_add() is split to two parts: a core function to add the
control element and a part calling it. The former is called from the
function for adding a user control element inside the controls_rwsem.
One change to be noted is that snd_ctl_notify() for adding a control
element gets called inside the controls_rwsem as well while it was
called outside the rwsem. But this should be OK, as snd_ctl_notify()
takes another (finer) rwlock instead of rwsem, and the call of
snd_ctl_notify() inside rwsem is already done in another code path.
Reported-by: syzbot+dc09047bce3820621ba2@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
-rw-r--r-- | sound/core/control.c | 80 |
1 files changed, 45 insertions, 35 deletions
diff --git a/sound/core/control.c b/sound/core/control.c index 9aa15bfc7936..649d3217590e 100644 --- a/sound/core/control.c +++ b/sound/core/control.c @@ -348,6 +348,40 @@ static int snd_ctl_find_hole(struct snd_card *card, unsigned int count) return 0; } +/* add a new kcontrol object; call with card->controls_rwsem locked */ +static int __snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol) +{ + struct snd_ctl_elem_id id; + unsigned int idx; + unsigned int count; + + id = kcontrol->id; + if (id.index > UINT_MAX - kcontrol->count) + return -EINVAL; + + if (snd_ctl_find_id(card, &id)) { + dev_err(card->dev, + "control %i:%i:%i:%s:%i is already present\n", + id.iface, id.device, id.subdevice, id.name, id.index); + return -EBUSY; + } + + if (snd_ctl_find_hole(card, kcontrol->count) < 0) + return -ENOMEM; + + list_add_tail(&kcontrol->list, &card->controls); + card->controls_count += kcontrol->count; + kcontrol->id.numid = card->last_numid + 1; + card->last_numid += kcontrol->count; + + id = kcontrol->id; + count = kcontrol->count; + for (idx = 0; idx < count; idx++, id.index++, id.numid++) + snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_ADD, &id); + + return 0; +} + /** * snd_ctl_add - add the control instance to the card * @card: the card instance @@ -364,45 +398,18 @@ static int snd_ctl_find_hole(struct snd_card *card, unsigned int count) */ int snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol) { - struct snd_ctl_elem_id id; - unsigned int idx; - unsigned int count; int err = -EINVAL; if (! kcontrol) return err; if (snd_BUG_ON(!card || !kcontrol->info)) goto error; - id = kcontrol->id; - if (id.index > UINT_MAX - kcontrol->count) - goto error; down_write(&card->controls_rwsem); - if (snd_ctl_find_id(card, &id)) { - up_write(&card->controls_rwsem); - dev_err(card->dev, "control %i:%i:%i:%s:%i is already present\n", - id.iface, - id.device, - id.subdevice, - id.name, - id.index); - err = -EBUSY; - goto error; - } - if (snd_ctl_find_hole(card, kcontrol->count) < 0) { - up_write(&card->controls_rwsem); - err = -ENOMEM; - goto error; - } - list_add_tail(&kcontrol->list, &card->controls); - card->controls_count += kcontrol->count; - kcontrol->id.numid = card->last_numid + 1; - card->last_numid += kcontrol->count; - id = kcontrol->id; - count = kcontrol->count; + err = __snd_ctl_add(card, kcontrol); up_write(&card->controls_rwsem); - for (idx = 0; idx < count; idx++, id.index++, id.numid++) - snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_ADD, &id); + if (err < 0) + goto error; return 0; error: @@ -1361,9 +1368,12 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file, kctl->tlv.c = snd_ctl_elem_user_tlv; /* This function manage to free the instance on failure. */ - err = snd_ctl_add(card, kctl); - if (err < 0) - return err; + down_write(&card->controls_rwsem); + err = __snd_ctl_add(card, kctl); + if (err < 0) { + snd_ctl_free_one(kctl); + goto unlock; + } offset = snd_ctl_get_ioff(kctl, &info->id); snd_ctl_build_ioff(&info->id, kctl, offset); /* @@ -1374,10 +1384,10 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file, * which locks the element. */ - down_write(&card->controls_rwsem); card->user_ctl_count++; - up_write(&card->controls_rwsem); + unlock: + up_write(&card->controls_rwsem); return 0; } |