4.9-stable review patch. If anyone has any objections, please let me know.
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From: Takashi Iwai tiwai@suse.de
commit e1a7bfe3807974e66f971f2589d4e0197ec0fced upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- sound/core/control.c | 80 ++++++++++++++++++++++++++++----------------------- 1 file changed, 45 insertions(+), 35 deletions(-)
--- a/sound/core/control.c +++ b/sound/core/control.c @@ -346,6 +346,40 @@ static int snd_ctl_find_hole(struct snd_ 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 @@ -362,45 +396,18 @@ static int snd_ctl_find_hole(struct snd_ */ 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: @@ -1354,9 +1361,12 @@ static int snd_ctl_elem_add(struct snd_c 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); /* @@ -1367,10 +1377,10 @@ static int snd_ctl_elem_add(struct snd_c * 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; }