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Message-ID: <b4519134-3053-f80a-ac03-3301abd9e63a@xs4all.nl>
Date: Fri, 12 Apr 2019 13:23:37 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Sumit Gupta <sumitg@...dia.com>, mchehab@...nel.org,
sakari.ailus@...ux.intel.com, paul.kocialkowski@...tlin.com,
tfiga@...omium.org, keiichiw@...omium.org, bbasu@...dia.com
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch V2] v4l2-core: fix use-after-free error
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
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