Re: [PATCH] iptables-restore: move code to add_param_to_argv, cleanup (fix gcc-4.7)

[Eric Dumazet <eric.dumazet@gmail.com>]

On Mon, 2012-07-23 at 12:38 +0200, pablo@netfilter.org wrote:
> From: Pablo Neira Ayuso <pablo@netfilter.org>
> 
> This patch seems to be a mere cleanup that moves the parameter parsing
> code to add_param_to_argv.
> 
> But, in reality, it also fixes iptables whe compiled with gcc-4.7.
> 
> Moving param_buffer declaration out of the loop seems to resolve the
> issue. gcc-4.7 seems to be generating bad code regarding param_buffer.
> 
> @@ -380,9 +380,9 @@
>                         quote_open = 0;
>                         escaped = 0;
>                         param_len = 0;
> +                       char param_buffer[1024];
> 
>                         for (curchar = parsestart; *curchar; curchar++) {
> -                               char param_buffer[1024];
> 
>                                 if (quote_open) {
>                                         if (escaped) {
> 
> But I have hard time to apply this patch in such a way. Instead, I came
> up with the idea of this cleanup, which does not harm after all (and fixes
> the issue for us).
> 
> Sorry, I didn't have the time to further debug this issue, but it would be
> worth to investigate what's going wrong and ping gcc people.

Bug seems that iptables forgot that "char param_buffer[1024];" can
disappear at the end of the block :

for (curchar = parsestart; *curchar; curchar++) {
	char param_buffer[1024];
	...
}

// here param_buffer[1024] is lost, so any var pointing 
// to it can mess stack

previous gcc were probably not so aggressive.