Re: [PATCH 5/5] attr: avoid multiple definition of hidden variable

[Pablo Neira Ayuso <pablo@netfilter.org>]

On 11/11/10 00:08, Jan Engelhardt wrote:
> When nesting two mnl_attr_for_each loops, the __len__ variable will be
> declared twice, eliciting a warning when -Wshadow is turned on. There
> can also be warnings in pre-C99 because declarations and code are
> mixed. Do without any temporaries that are not explicitly specified as
> macro parameters.

I like this spot, some question below:

> Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
[...]
> diff --git a/src/attr.c b/src/attr.c
> index e22a8ac..5137395 100644
> --- a/src/attr.c
> +++ b/src/attr.c
> @@ -106,9 +106,8 @@ bool mnl_attr_ok(const struct nlattr *attr, int len)
>   * as parameter. You have to use mnl_attr_ok() to ensure that the next
>   * attribute is valid.
>   */
> -struct nlattr *mnl_attr_next(const struct nlattr *attr, int *len)
> +struct nlattr *mnl_attr_next(const struct nlattr *attr)
>  {
> -	*len -= MNL_ALIGN(attr->nla_len);
>  	return (struct nlattr *)((void *)attr + MNL_ALIGN(attr->nla_len));
>  }

If we remove the len parameter from mnl_attr_next(), we may access
memory that may be out of the message boundary in mnl_attr_ok().