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Message-ID: <30ea73dc-7be7-1fe4-5270-fb94df5184e9@xs4all.nl>
Date: Fri, 12 Apr 2019 15:55:44 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Sumit Gupta <sumitg@...dia.com>,
"mchehab@...nel.org" <mchehab@...nel.org>,
"sakari.ailus@...ux.intel.com" <sakari.ailus@...ux.intel.com>,
"paul.kocialkowski@...tlin.com" <paul.kocialkowski@...tlin.com>,
"tfiga@...omium.org" <tfiga@...omium.org>,
"keiichiw@...omium.org" <keiichiw@...omium.org>,
Bibek Basu <bbasu@...dia.com>
Cc: "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Patch V2] v4l2-core: fix use-after-free error
On 4/12/19 3:47 PM, Sumit Gupta wrote:
>
> On 4/11/19 6:01 PM, Sumit Gupta wrote:
>> From: sumitg <sumitg@...dia.com>
>>
>> Fixing use-after-free within __v4l2_ctrl_handler_setup().
>> Memory is being freed with kfree(new_ref) for duplicate control
>> reference entry but cluster is still referring to the duplicate entry.
>> Change done to update ctrl->cluster only when new control reference is
>> added. Also, checking if
>> ctrl->ncontrols is non-zero before accessing controls from
>> cluster pointer to avoid illegal access when cluster has zero
>> controls.
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in __v4l2_ctrl_handler_setup+0x388/0x428
>> Read of size 8 at addr ffffffc324e78618 by task systemd-udevd/312
>>
>> Allocated by task 312:
>>
>> Freed by task 312:
>>
>> The buggy address belongs to the object at ffffffc324e78600
>> which belongs to the cache kmalloc-64 of size 64 The buggy address
>> is located 24 bytes inside of
>> 64-byte region [ffffffc324e78600, ffffffc324e78640) The buggy
>> address belongs to the page:
>> page:ffffffbf0c939e00 count:1 mapcount:0 mapping:
>> (null) index:0xffffffc324e78f80
>> flags: 0x4000000000000100(slab)
>> raw: 4000000000000100 0000000000000000 ffffffc324e78f80
>> 000000018020001a
>> raw: 0000000000000000 0000000100000001 ffffffc37040fb80
>> 0000000000000000 page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>> ffffffc324e78500: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>> ffffffc324e78580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>> >ffffffc324e78600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>> ^
>> ffffffc324e78680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>> ffffffc324e78700: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
>> ==================================================================
>>
>> Suggested-by: Hans Verkuil <hverkuil-cisco@...all.nl>
>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
>> ---
>> v2:
>> * update ctrl->cluster only when new control reference is added.
>> * check ctrl->ncontrols to avoid illegal access when cluster has zero controls.
>>
>> drivers/media/v4l2-core/v4l2-ctrls.c | 53
>> +++++++++++++++++++-----------------
>> 1 file changed, 28 insertions(+), 25 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c
>> b/drivers/media/v4l2-core/v4l2-ctrls.c
>> index 5e3806f..3d0a952 100644
>> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
>> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
>> @@ -2154,15 +2154,6 @@ static int handler_new_ref(struct v4l2_ctrl_handler *hdl,
>> if (size_extra_req)
>> new_ref->p_req.p = &new_ref[1];
>>
>> - if (ctrl->handler == hdl) {
>> - /* By default each control starts in a cluster of its own.
>> - new_ref->ctrl is basically a cluster array with one
>> - element, so that's perfect to use as the cluster pointer.
>> - But only do this for the handler that owns the control. */
>> - ctrl->cluster = &new_ref->ctrl;
>> - ctrl->ncontrols = 1;
>> - }
>> -
>> INIT_LIST_HEAD(&new_ref->node);
>>
>> mutex_lock(hdl->lock);
>> @@ -2195,6 +2186,15 @@ static int handler_new_ref(struct v4l2_ctrl_handler *hdl,
>> hdl->buckets[bucket] = new_ref;
>> if (ctrl_ref)
>> *ctrl_ref = new_ref;
>> + if (ctrl->handler == hdl) {
>> + /* By default each control starts in a cluster of its own.
>> + * new_ref->ctrl is basically a cluster array with one
>> + * element, so that's perfect to use as the cluster pointer.
>> + * But only do this for the handler that owns the control.
>> + */
>> + ctrl->cluster = &new_ref->ctrl;
>> + ctrl->ncontrols = 1;
>> + }
>>
>> unlock:
>> mutex_unlock(hdl->lock);
>
> This looks good.
>
>> @@ -2725,25 +2725,28 @@ int __v4l2_ctrl_handler_setup(struct v4l2_ctrl_handler *hdl)
>> ctrl->done = false;
>>
>> list_for_each_entry(ctrl, &hdl->ctrls, node) {
>> - struct v4l2_ctrl *master = ctrl->cluster[0];
>> - int i;
>> -
>> - /* Skip if this control was already handled by a cluster. */
>> - /* Skip button controls and read-only controls. */
>> - if (ctrl->done || ctrl->type == V4L2_CTRL_TYPE_BUTTON ||
>> - (ctrl->flags & V4L2_CTRL_FLAG_READ_ONLY))
>> - continue;
>> + if (ctrl->ncontrols) {
>> + struct v4l2_ctrl *master = ctrl->cluster[0];
>> + int i;
>> +
>> + /* Skip if this control was already handled by a */
>> + /* cluster. Skip button controls and read-only */
>> + /* controls. */
>> + if (ctrl->done || ctrl->type == V4L2_CTRL_TYPE_BUTTON ||
>> + (ctrl->flags & V4L2_CTRL_FLAG_READ_ONLY))
>> + continue;
>>
>> - for (i = 0; i < master->ncontrols; i++) {
>> - if (master->cluster[i]) {
>> - cur_to_new(master->cluster[i]);
>> - master->cluster[i]->is_new = 1;
>> - master->cluster[i]->done = true;
>> + for (i = 0; i < master->ncontrols; i++) {
>> + if (master->cluster[i]) {
>> + cur_to_new(master->cluster[i]);
>> + master->cluster[i]->is_new = 1;
>> + master->cluster[i]->done = true;
>> + }
>> }
>> + ret = call_op(master, s_ctrl);
>> + if (ret)
>> + break;
>> }
>> - ret = call_op(master, s_ctrl);
>> - if (ret)
>> - break;
>> }
>>
>> return ret;
>>
>
> These changes shouldn't be needed: when you get here all controls are guaranteed to have a non-0 ncontrols value.
>
> If it is possible to encounter a control where ncontrols == 0, then that's a bug elsewhere. But as far as I can tell that isn't the case.
>
> Regards,
>
> Hans
>
> Yes, I am getting a control where ncontrols is zero as printed below.
> It can be another bug as you said. I think, adding check here will be
> helpful to not crash in such cases. Please share if you think otherwise,
> then will remove the check.
>
> int __v4l2_ctrl_handler_setup(struct v4l2_ctrl_handler *hdl)
> ctrl->done = false;
>
> list_for_each_entry(ctrl, &hdl->ctrls, node) {
> + if (ctrl->ncontrols == 0)
> + pr_crit("<func:%s><ctrl->name:%s><ctrl->ncontrols:%d>\n",
> + __func__, ctrl->name, ctrl->ncontrols);
>
> Log:
> [ 8.354464] <func:__v4l2_ctrl_handler_setup><ctrl->name:Group Hold><ctrl->ncontrols:0>
Something went wrong if you get this.
This should never happen. Dig a bit deeper to find out how you get into this situation.
You did check hdl->error before calling v4l2_ctrl_handler_setup? Although even if an error
occurred when adding controls, this should still not happen.
Regards,
Hans
>
>
> Regards,
> Sumit Gupta
>
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