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Subject[Patch V2] v4l2-core: fix use-after-free error
Date
From: sumitg <sumitg@nvidia.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@xs4all.nl>
Signed-off-by: Sumit Gupta <sumitg@nvidia.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);
@@ -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;
--
2.7.4
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