[LEDE-DEV] [PATCH] uci: fix a potential use-after-free in uci_set()

[Hans Dedecker]

On Tue, Mar 13, 2018 at 3:44 AM, Jordan Miner <jminer7 at gmail.com> wrote:
> When calling uci_set() to update an option, if ptr->o != NULL and
> ptr->option == NULL, then uci_expand_ptr() will set ptr->option to
> ptr->o->e.name (or the caller could set ptr->option to that value). In
> this case, the option will be freed just before calling
> uci_alloc_option() with ptr->option, which was just freed.
>
> Signed-off-by: Jordan Miner <jminer7 at gmail.com>
> ---
>  list.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/list.c b/list.c
> index 0347138..5a1d891 100644
> --- a/list.c
> +++ b/list.c
> @@ -698,8 +698,8 @@ int uci_set(struct uci_context *ctx, struct uci_ptr *ptr)
>                 if ((ptr->o->type == UCI_TYPE_STRING) &&
>                         !strcmp(ptr->o->v.string, ptr->value))
>                         return 0;
> -               uci_free_option(ptr->o);
>                 ptr->o = uci_alloc_option(ptr->s, ptr->option, ptr->value);
> +               uci_free_option(ptr->o);
This introduces a memory leak now as the old option is overridden by
the newly allocated option which is immediately freed

Hans
>                 ptr->last = &ptr->o->e;
>         } else if (ptr->s && ptr->section) { /* update section */
>                 char *s = uci_strdup(ctx, ptr->value);
> --
> 2.7.4
>
>
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