[PATCH] udhcpc: fixed option_ip_pair parsing

[Vladislav Grishenko]

> From: Denys Vlasenko
> Sent: Sunday, October 17, 2010 4:27 PM
> Cc: Vladislav Grishenko
> Subject: Re: [PATCH] udhcpc: fixed option_ip_pair parsing
> 
> On Sunday 17 October 2010 10:25, Vladislav Grishenko wrote:
> > Hello,
> > Sorry, previous message doesn't include description.
> >
> > Commit
> >
> http://git.busybox.net/busybox/commit/?id=7d3a48a003cd645edfae2b4044
> 93
> > 688022
> > b13193
> > revealed incorrect OPTION_IP_PAIR implementation, which doesn't
> > respect option length and causes erroneous classful routes, composed
> > from garbage or first bytes from the next  DHCP packet option.
> > Patch is attached.
> 
> Good catch!
> I propose the fix which is less mind-bending: remove all +/-4 tricks in
> OPTION_IP_PAIR (they are hard to follow and that's why they contained a
> sublte bug), and add ip_ofs variable which may be used to advance "option"
> pointer in OPTION_IP:
> 
>         while (len >= optlen) {
> +               unsigned ip_ofs = 0;
> 
>                 switch (type) {
>                 case OPTION_IP_PAIR:
>                         dest += sprint_nip(dest, "", option);
>                         *dest++ = '/';
> -                       option += 4;
> -                       optlen = 4;
> +                       ip_ofs = 4;
>                         /* fall through */
>                 case OPTION_IP:
> -                       dest += sprint_nip(dest, "", option);
> +                       dest += sprint_nip(dest, "", option + ip_ofs);
>                         break;
> 
> 
> --
> vda

Yep, it looks cute.
Denys, do we really need to zero ip_opt in each loop? Option type remains const in this function.

Best Regards, theMIROn
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Skype: the.miron