netdev - Re: [PATCH] iproute2: Conforming to -D_FORTIFY

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Message-ID: <20111017082307.46a994a8@nehalam.linuxnetplumber.net>
Date:	Mon, 17 Oct 2011 08:23:07 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Bin Li <libin.charles@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] iproute2: Conforming to -D_FORTIFY_SOURCE=2
 restrictions

On Mon, 17 Oct 2011 15:35:35 +0800
Bin Li <libin.charles@...il.com> wrote:

> (gdb) l
> 161                     len = slen;
> 162                     if (len > 0) {
> 163                             if (len > max)
> 164                                     invarg("\"ALGOKEY\" makes buffer
> overflow\n", key);
> 165
> 166                             strncpy(buf, key, len);
> 167                     }
> 168             }
> 169
> 170             alg->alg_key_len = len * 8;
> (gdb) up
> #8  xfrm_state_modify (cmd=<optimized out>, flags=<optimized out>, argc=1,
>     argv=0x7fffffffe370) at xfrm_state.c:406
> 406                                     xfrm_algo_parse((void *)&alg, type,
> name, key,
> 
> the compiler passes zero to __builtin___strncpy_chk as the buffer size.
> xfrm_algo_parse is inlined into xfrm_state_modify.

I don't understand, looks like a compiler bug. Call strncpy with
0 length should not be possible since the check was  3 lines
before for len > 0.
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