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References: <20220408172103.371637-1-frowand.list@gmail.com>
In-Reply-To: <20220408172103.371637-1-frowand.list@gmail.com>
From:   Rob Herring <robh+dt@kernel.org>
Date:   Fri, 8 Apr 2022 12:34:03 -0500
Message-ID: <CAL_JsqJC6pKxEmwMeirVLwJEbOH0WD+01VEfFXC257a+ZDRtsw@mail.gmail.com>
Subject: Re: [PATCH 1/1] of: overlay: of_overlay_apply() kfree() errors
To:     Frank Rowand <frowand.list@gmail.com>
Cc:     Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
        Slawomir Stepien <slawomir.stepien@nokia.com>,
        devicetree@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Slawomir Stepien <sst@poczta.fm>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Alan Tull <atull@kernel.org>
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On Fri, Apr 8, 2022 at 12:21 PM <frowand.list@gmail.com> wrote:
>
> From: Frank Rowand <frank.rowand@sony.com>

The subject needs a verb.

>
> 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:).

What about my question/suggestion on the original patch from Slawomir?

>
> Double kfree()
> Reported-by: Slawomir Stepien <slawomir.stepien@nokia.com>
>
> Signed-off-by: Frank Rowand <frank.rowand@sony.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);
>         kfree(new_fdt);
>
>  out:
> --
> Frank Rowand <frank.rowand@sony.com>
>