Date:   Sun, 10 Apr 2022 15:22:50 -0500
From:   Frank Rowand <frowand.list@...il.com>
To:     Slawomir Stepien <sst@...zta.fm>
Cc:     Rob Herring <robh+dt@...nel.org>, pantelis.antoniou@...sulko.com,
        Slawomir Stepien <slawomir.stepien@...ia.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Alan Tull <atull@...nel.org>
Subject: Re: [PATCH 1/1] of: overlay: of_overlay_apply() kfree() errors

On 4/9/22 01:52, Slawomir Stepien wrote:
> On kwi 08, 2022 12:21, frowand.list@...il.com wrote:
>> From: Frank Rowand <frank.rowand@...y.com>
> 
> Hi Frank!
> 
> See my one comment below.
> 
>> Fix various kfree() issues related to of_overlay_apply().
>>   - Double kfree() of fdt and tree when init_overlay_changeset()
>>     returns an error.
>>   - free_overlay_changeset() free of the root of the unflattened
>>     overlay (variable tree) instead of the memory that contains
>>     the unflattened overlay.
>>   - Move similar kfree()s from multiple error locations to a
>>     common error path (err_free_tree_unlocked:).
>>
>> Double kfree()
>> Reported-by: Slawomir Stepien <slawomir.stepien@...ia.com>
>>
>> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
>> ---
>>  drivers/of/overlay.c | 64 ++++++++++++++++++++++++++++----------------
>>  1 file changed, 41 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
>> index d80160cf34bb..1b9a90d61496 100644
>> --- a/drivers/of/overlay.c
>> +++ b/drivers/of/overlay.c
>> @@ -58,6 +58,7 @@ struct fragment {
>>   * @id:			changeset identifier
>>   * @ovcs_list:		list on which we are located
>>   * @fdt:		base of memory allocated to hold aligned FDT that was unflattened to create @overlay_tree
>> + * @overlay_mem:	the memory chunk that contains @overlay_tree
>>   * @overlay_tree:	expanded device tree that contains the fragment nodes
>>   * @count:		count of fragment structures
>>   * @fragments:		fragment nodes in the overlay expanded device tree
>> @@ -68,6 +69,7 @@ struct overlay_changeset {
>>  	int id;
>>  	struct list_head ovcs_list;
>>  	const void *fdt;
>> +	const void *overlay_mem;
>>  	struct device_node *overlay_tree;
>>  	int count;
>>  	struct fragment *fragments;
>> @@ -720,6 +722,7 @@ static struct device_node *find_target(struct device_node *info_node)
>>   * init_overlay_changeset() - initialize overlay changeset from overlay tree
>>   * @ovcs:	Overlay changeset to build
>>   * @fdt:	base of memory allocated to hold aligned FDT that was unflattened to create @tree
>> + * @tree_mem:	Memory that contains @tree
>>   * @tree:	Contains the overlay fragments and overlay fixup nodes
>>   *
>>   * Initialize @ovcs.  Populate @ovcs->fragments with node information from
>> @@ -730,13 +733,23 @@ static struct device_node *find_target(struct device_node *info_node)
>>   * detected in @tree, or -ENOSPC if idr_alloc() error.
>>   */
>>  static int init_overlay_changeset(struct overlay_changeset *ovcs,
>> -		const void *fdt, struct device_node *tree)
>> +		const void *fdt, const void *tree_mem, struct device_node *tree)
>>  {
>>  	struct device_node *node, *overlay_node;
>>  	struct fragment *fragment;
>>  	struct fragment *fragments;
>>  	int cnt, id, ret;
>>  
>> +	/*
>> +	 * Must set these fields before any error return. fdt and tree_mem
>> +	 * will be freed by free_overlay_changeset(), which is called if
>> +	 * init_overlay_changeset() returns an error.
>> +	 */
>> +
>> +	ovcs->fdt = fdt;
>> +	ovcs->overlay_mem = tree_mem;
>> +	ovcs->overlay_tree = tree;
>> +
>>  	/*
>>  	 * Warn for some issues.  Can not return -EINVAL for these until
>>  	 * of_unittest_apply_overlay() is fixed to pass these checks.
>> @@ -750,9 +763,6 @@ static int init_overlay_changeset(struct overlay_changeset *ovcs,
>>  	if (!of_node_is_root(tree))
>>  		pr_debug("%s() tree is not root\n", __func__);
>>  
>> -	ovcs->overlay_tree = tree;
>> -	ovcs->fdt = fdt;
>> -
>>  	INIT_LIST_HEAD(&ovcs->ovcs_list);
>>  
>>  	of_changeset_init(&ovcs->cset);
>> @@ -865,7 +875,7 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
>>  	 * ovcs->fdt due to the policy that overlay notifiers are not allowed
>>  	 * to retain pointers into the overlay devicetree.
>>  	 */
>> -	kfree(ovcs->overlay_tree);
>> +	kfree(ovcs->overlay_mem);
>>  	kfree(ovcs->fdt);
>>  	kfree(ovcs);
>>  }
>> @@ -875,6 +885,7 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
>>   *
>>   * of_overlay_apply() - Create and apply an overlay changeset
>>   * @fdt:	base of memory allocated to hold the aligned FDT
>> + * @tree_mem:	Memory that contains @tree
>>   * @tree:	Expanded overlay device tree
>>   * @ovcs_id:	Pointer to overlay changeset id
>>   *
>> @@ -913,31 +924,27 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
>>   * id is returned to *ovcs_id.
>>   */
>>  
>> -static int of_overlay_apply(const void *fdt, struct device_node *tree,
>> -		int *ovcs_id)
>> +static int of_overlay_apply(const void *fdt, void *tree_mem,
>> +		struct device_node *tree, int *ovcs_id)
>>  {
>>  	struct overlay_changeset *ovcs;
>>  	int ret = 0, ret_revert, ret_tmp;
>>  
>>  	/*
>> -	 * As of this point, fdt and tree belong to the overlay changeset.
>> +	 * As of this point, fdt and tree_mem belong to the overlay changeset.
>>  	 * overlay changeset code is responsible for freeing them.
>>  	 */
>>  
>>  	if (devicetree_corrupt()) {
>>  		pr_err("devicetree state suspect, refuse to apply overlay\n");
>> -		kfree(fdt);
>> -		kfree(tree);
>>  		ret = -EBUSY;
>> -		goto out;
>> +		goto err_free_tree_unlocked;
>>  	}
>>  
>>  	ovcs = kzalloc(sizeof(*ovcs), GFP_KERNEL);
>>  	if (!ovcs) {
>> -		kfree(fdt);
>> -		kfree(tree);
>>  		ret = -ENOMEM;
>> -		goto out;
>> +		goto err_free_tree_unlocked;
>>  	}
>>  
>>  	of_overlay_mutex_lock();
>> @@ -947,9 +954,14 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree,
>>  	if (ret)
>>  		goto err_free_tree;
>>  
>> -	ret = init_overlay_changeset(ovcs, fdt, tree);
>> +	/*
>> +	 * init_overlay_changeset() promises to add tree_mem and tree to ovcs
>> +	 * even in the case of an early error return, so they can be freed by
>> +	 * free_overlay_changeset().
>> +	 */
>> +	ret = init_overlay_changeset(ovcs, fdt, tree_mem, tree);
>>  	if (ret)
>> -		goto err_free_tree;
>> +		goto err_free_overlay_changeset;
>>  
>>  	/*
>>  	 * after overlay_notify(), ovcs->overlay_tree related pointers may have
>> @@ -999,7 +1011,7 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree,
>>  
>>  err_free_tree:
>>  	kfree(fdt);
>> -	kfree(tree);
>> +	kfree(tree_mem);
>>  
>>  err_free_overlay_changeset:
>>  	free_overlay_changeset(ovcs);
>> @@ -1008,9 +1020,14 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree,
>>  	mutex_unlock(&of_mutex);
>>  	of_overlay_mutex_unlock();
>>  
>> -out:
>>  	pr_debug("%s() err=%d\n", __func__, ret);
>>  
>> +	return ret;
>> +
>> +err_free_tree_unlocked:
>> +	kfree(fdt);
>> +	kfree(tree_mem);
>> +
>>  	return ret;
>>  }
>>  
>> @@ -1019,6 +1036,7 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
>>  {
>>  	void *new_fdt;
>>  	void *new_fdt_align;
>> +	void *overlay_mem;
>>  	int ret;
>>  	u32 size;
>>  	struct device_node *overlay_root = NULL;
>> @@ -1046,18 +1064,17 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
>>  	new_fdt_align = PTR_ALIGN(new_fdt, FDT_ALIGN_SIZE);
>>  	memcpy(new_fdt_align, overlay_fdt, size);
>>  
>> -	of_fdt_unflatten_tree(new_fdt_align, NULL, &overlay_root);
>> -	if (!overlay_root) {
>> +	overlay_mem = of_fdt_unflatten_tree(new_fdt_align, NULL, &overlay_root);
>> +	if (!overlay_mem) {
>>  		pr_err("unable to unflatten overlay_fdt\n");
>>  		ret = -EINVAL;
>>  		goto out_free_new_fdt;
>>  	}
>>  
>> -	ret = of_overlay_apply(new_fdt, overlay_root, ovcs_id);
>> +	ret = of_overlay_apply(new_fdt, overlay_mem, overlay_root, ovcs_id);
>>  	if (ret < 0) {
>>  		/*
>> -		 * new_fdt and overlay_root now belong to the overlay
>> -		 * changeset.
>> +		 * new_fdt and overlay_mem now belong to the overlay changeset.
>>  		 * overlay changeset code is responsible for freeing them.
>>  		 */
>>  		goto out;
>> @@ -1067,6 +1084,7 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
>>  
>>  
>>  out_free_new_fdt:
>> +	kfree(overlay_mem);
> 
> There is no need to free this overlay_mem. You can end up here only when
> overlay_mem is NULL.

Thanks for catching this.

There will be a new very different version of this patch reflecting Rob's
comments.

-Frank

> 
>>  	kfree(new_fdt);
>>  
>>  out:
> 

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