media: v4l2-ctrls: fix reference to freed memory

When controls are used together with the Request API, then for
each request a v4l2_ctrl_handler struct is allocated. This contains
the controls that can be set in a request. If a control is *not* set in
the request, then the value used in the most recent previous request
must be used, or the current value if it is not found in any outstanding
requests.

The framework tried to find such a previous request and it would set
the 'req' pointer in struct v4l2_ctrl_ref to the v4l2_ctrl_ref of the
control in such a previous request. So far, so good. However, when that
previous request was applied to the hardware, returned to userspace, and
then userspace would re-init or free that request, any 'ref' pointer in
still-queued requests would suddenly point to freed memory.

This was not noticed before since the drivers that use this expected
that each request would always have the controls set, so there was
never any need to find a control in older requests. This requirement
was relaxed, and now this bug surfaced.

It was also made worse by changeset
2fae4d6aabc8 ("media: v4l2-ctrls: v4l2_ctrl_request_complete() should always set ref->req")
which increased the chance of this happening.

The use of the 'req' pointer in v4l2_ctrl_ref was very fragile, so
drop this entirely. Instead add a valid_p_req bool to indicate that
p_req contains a valid value for this control. And if it is false,
then just use the current value of the control.

Note that VIDIOC_G_EXT_CTRLS will always return -EACCES when attempting
to get a control from a request until the request is completed. And in
that case, all controls in the request will have the control value set
(i.e. valid_p_req is true). This means that the whole 'find the most
recent previous request containing a control' idea is pointless, and
the code can be simplified considerably.

The v4l2_g_ext_ctrls_common() function was refactored a bit to make
it more understandable. It also avoids updating volatile controls
in a completed request since that was already done when the request
was completed.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Fixes: 2fae4d6aabc8 ("media: v4l2-ctrls: v4l2_ctrl_request_complete() should always set ref->req")
Fixes: 6fa6f831f095 ("media: v4l2-ctrls: add core request support")
Cc: <stable@vger.kernel.org>      # for v5.9 and up
Tested-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 63 insertions, 74 deletions

diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index c7bcc5c25771..0d7fe1bd975a 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -2504,7 +2504,16 @@ static void new_to_req(struct v4l2_ctrl_ref *ref)
 	if (!ref)
 		return;
 	ptr_to_ptr(ref->ctrl, ref->ctrl->p_new, ref->p_req);
-	ref->req = ref;
+	ref->valid_p_req = true;
+}
+
+/* Copy the current value to the request value */
+static void cur_to_req(struct v4l2_ctrl_ref *ref)
+{
+	if (!ref)
+		return;
+	ptr_to_ptr(ref->ctrl, ref->ctrl->p_cur, ref->p_req);
+	ref->valid_p_req = true;
 }
 
 /* Copy the request value to the new value */
@@ -2512,8 +2521,8 @@ static void req_to_new(struct v4l2_ctrl_ref *ref)
 {
 	if (!ref)
 		return;
-	if (ref->req)
-		ptr_to_ptr(ref->ctrl, ref->req->p_req, ref->ctrl->p_new);
+	if (ref->valid_p_req)
+		ptr_to_ptr(ref->ctrl, ref->p_req, ref->ctrl->p_new);
 	else
 		ptr_to_ptr(ref->ctrl, ref->ctrl->p_cur, ref->ctrl->p_new);
 }
@@ -3694,39 +3703,8 @@ static void v4l2_ctrl_request_queue(struct media_request_object *obj)
 	struct v4l2_ctrl_handler *hdl =
 		container_of(obj, struct v4l2_ctrl_handler, req_obj);
 	struct v4l2_ctrl_handler *main_hdl = obj->priv;
-	struct v4l2_ctrl_handler *prev_hdl = NULL;
-	struct v4l2_ctrl_ref *ref_ctrl, *ref_ctrl_prev = NULL;
 
 	mutex_lock(main_hdl->lock);
-	if (list_empty(&main_hdl->requests_queued))
-		goto queue;
-
-	prev_hdl = list_last_entry(&main_hdl->requests_queued,
-				   struct v4l2_ctrl_handler, requests_queued);
-	/*
-	 * Note: prev_hdl and hdl must contain the same list of control
-	 * references, so if any differences are detected then that is a
-	 * driver bug and the WARN_ON is triggered.
-	 */
-	mutex_lock(prev_hdl->lock);
-	ref_ctrl_prev = list_first_entry(&prev_hdl->ctrl_refs,
-					 struct v4l2_ctrl_ref, node);
-	list_for_each_entry(ref_ctrl, &hdl->ctrl_refs, node) {
-		if (ref_ctrl->req)
-			continue;
-		while (ref_ctrl_prev->ctrl->id < ref_ctrl->ctrl->id) {
-			/* Should never happen, but just in case... */
-			if (list_is_last(&ref_ctrl_prev->node,
-					 &prev_hdl->ctrl_refs))
-				break;
-			ref_ctrl_prev = list_next_entry(ref_ctrl_prev, node);
-		}
-		if (WARN_ON(ref_ctrl_prev->ctrl->id != ref_ctrl->ctrl->id))
-			break;
-		ref_ctrl->req = ref_ctrl_prev->req;
-	}
-	mutex_unlock(prev_hdl->lock);
-queue:
 	list_add_tail(&hdl->requests_queued, &main_hdl->requests_queued);
 	hdl->request_is_queued = true;
 	mutex_unlock(main_hdl->lock);
@@ -3783,7 +3761,7 @@ v4l2_ctrl_request_hdl_ctrl_find(struct v4l2_ctrl_handler *hdl, u32 id)
 {
 	struct v4l2_ctrl_ref *ref = find_ref_lock(hdl, id);
 
-	return (ref && ref->req == ref) ? ref->ctrl : NULL;
+	return (ref && ref->valid_p_req) ? ref->ctrl : NULL;
 }
 EXPORT_SYMBOL_GPL(v4l2_ctrl_request_hdl_ctrl_find);
 
@@ -3972,7 +3950,13 @@ static int class_check(struct v4l2_ctrl_handler *hdl, u32 which)
 	return find_ref_lock(hdl, which | 1) ? 0 : -EINVAL;
 }
 
-/* Get extended controls. Allocates the helpers array if needed. */
+/*
+ * Get extended controls. Allocates the helpers array if needed.
+ *
+ * Note that v4l2_g_ext_ctrls_common() with 'which' set to
+ * V4L2_CTRL_WHICH_REQUEST_VAL is only called if the request was
+ * completed, and in that case valid_p_req is true for all controls.
+ */
 static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
 				   struct v4l2_ext_controls *cs,
 				   struct video_device *vdev)
@@ -3981,9 +3965,10 @@ static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
 	struct v4l2_ctrl_helper *helpers = helper;
 	int ret;
 	int i, j;
-	bool def_value;
+	bool is_default, is_request;
 
-	def_value = (cs->which == V4L2_CTRL_WHICH_DEF_VAL);
+	is_default = (cs->which == V4L2_CTRL_WHICH_DEF_VAL);
+	is_request = (cs->which == V4L2_CTRL_WHICH_REQUEST_VAL);
 
 	cs->error_idx = cs->count;
 	cs->which = V4L2_CTRL_ID2WHICH(cs->which);
@@ -4009,11 +3994,9 @@ static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
 			ret = -EACCES;
 
 	for (i = 0; !ret && i < cs->count; i++) {
-		int (*ctrl_to_user)(struct v4l2_ext_control *c,
-				    struct v4l2_ctrl *ctrl);
 		struct v4l2_ctrl *master;
-
-		ctrl_to_user = def_value ? def_to_user : cur_to_user;
+		bool is_volatile = false;
+		u32 idx = i;
 
 		if (helpers[i].mref == NULL)
 			continue;
@@ -4023,31 +4006,48 @@ static int v4l2_g_ext_ctrls_common(struct v4l2_ctrl_handler *hdl,
 
 		v4l2_ctrl_lock(master);
 
-		/* g_volatile_ctrl will update the new control values */
-		if (!def_value &&
+		/*
+		 * g_volatile_ctrl will update the new control values.
+		 * This makes no sense for V4L2_CTRL_WHICH_DEF_VAL and
+		 * V4L2_CTRL_WHICH_REQUEST_VAL. In the case of requests
+		 * it is v4l2_ctrl_request_complete() that copies the
+		 * volatile controls at the time of request completion
+		 * to the request, so you don't want to do that again.
+		 */
+		if (!is_default && !is_request &&
 		    ((master->flags & V4L2_CTRL_FLAG_VOLATILE) ||
 		    (master->has_volatiles && !is_cur_manual(master)))) {
 			for (j = 0; j < master->ncontrols; j++)
 				cur_to_new(master->cluster[j]);
 			ret = call_op(master, g_volatile_ctrl);
-			ctrl_to_user = new_to_user;
+			is_volatile = true;
 		}
-		/* If OK, then copy the current (for non-volatile controls)
-		   or the new (for volatile controls) control values to the
-		   caller */
-		if (!ret) {
-			u32 idx = i;
 
-			do {
-				if (helpers[idx].ref->req)
-					ret = req_to_user(cs->controls + idx,
-						helpers[idx].ref->req);
-				else
-					ret = ctrl_to_user(cs->controls + idx,
-						helpers[idx].ref->ctrl);
-				idx = helpers[idx].next;
-			} while (!ret && idx);
+		if (ret) {
+			v4l2_ctrl_unlock(master);
+			break;
 		}
+
+		/*
+		 * Copy the default value (if is_default is true), the
+		 * request value (if is_request is true and p_req is valid),
+		 * the new volatile value (if is_volatile is true) or the
+		 * current value.
+		 */
+		do {
+			struct v4l2_ctrl_ref *ref = helpers[idx].ref;
+
+			if (is_default)
+				ret = def_to_user(cs->controls + idx, ref->ctrl);
+			else if (is_request && ref->valid_p_req)
+				ret = req_to_user(cs->controls + idx, ref);
+			else if (is_volatile)
+				ret = new_to_user(cs->controls + idx, ref->ctrl);
+			else
+				ret = cur_to_user(cs->controls + idx, ref->ctrl);
+			idx = helpers[idx].next;
+		} while (!ret && idx);
+
 		v4l2_ctrl_unlock(master);
 	}
 
@@ -4690,8 +4690,6 @@ void v4l2_ctrl_request_complete(struct media_request *req,
 		unsigned int i;
 
 		if (ctrl->flags & V4L2_CTRL_FLAG_VOLATILE) {
-			ref->req = ref;
-
 			v4l2_ctrl_lock(master);
 			/* g_volatile_ctrl will update the current control values */
 			for (i = 0; i < master->ncontrols; i++)
@@ -4701,21 +4699,12 @@ void v4l2_ctrl_request_complete(struct media_request *req,
 			v4l2_ctrl_unlock(master);
 			continue;
 		}
-		if (ref->req == ref)
+		if (ref->valid_p_req)
 			continue;
 
+		/* Copy the current control value into the request */
 		v4l2_ctrl_lock(ctrl);
-		if (ref->req) {
-			ptr_to_ptr(ctrl, ref->req->p_req, ref->p_req);
-		} else {
-			ptr_to_ptr(ctrl, ctrl->p_cur, ref->p_req);
-			/*
-			 * Set ref->req to ensure that when userspace wants to
-			 * obtain the controls of this request it will take
-			 * this value and not the current value of the control.
-			 */
-			ref->req = ref;
-		}
+		cur_to_req(ref);
 		v4l2_ctrl_unlock(ctrl);
 	}
 
@@ -4779,7 +4768,7 @@ int v4l2_ctrl_request_setup(struct media_request *req,
 				struct v4l2_ctrl_ref *r =
 					find_ref(hdl, master->cluster[i]->id);
 
-				if (r->req && r == r->req) {
+				if (r->valid_p_req) {
 					have_new_data = true;
 					break;
 				}