linux-kernel - Re: [PATCH] init - fix building bug and potential buffer overflow

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Date:	Fri, 16 May 2008 00:22:14 +0400
From:	"Cyrill Gorcunov" <gorcunov@...il.com>
To:	"Geert Uytterhoeven" <geert@...ux-m68k.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Roman Zippel" <zippel@...ux-m68k.org>,
	"Andreas Schwab" <schwab@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Linux/m68k" <linux-m68k@...r.kernel.org>
Subject: Re: [PATCH] init - fix building bug and potential buffer overflow

Could you please make an update to the patch? I can make it only
tomorrow evening (ie not that fast)

On 5/15/08, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Thu, 15 May 2008, Cyrill Gorcunov wrote:
>> [Andrew Morton - Thu, May 15, 2008 at 10:58:03AM -0700]
>> | On Wed, 14 May 2008 19:44:02 +0400 Cyrill Gorcunov <gorcunov@...il.com>
>> wrote:
>> |
>> | > This patch does fix build bug on m68k wich does not have strncat in
>> straight way.
>> | >
>> | > What is more important - my previous patch
>> | >
>> | > commit e662e1cfd434aa234b72fbc781f1d70211cb785b
>> | > Author: Cyrill Gorcunov <gorcunov@...il.com>
>> | > Date:   Mon May 12 14:02:22 2008 -0700
>> | >
>> | >     init: don't lose initcall return values
>> | >
>> | > has introduced potential buffer overflow by wrong calculation
>> | > of string accumulator size.
>> | >
>> | > Many thanks Andreas Schwab and Geert Uytterhoeven for helping
>> | > to catch and fix the bug.
>> | >
>> | > Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
>> | > ---
>> | >
>> | > Index: linux-2.6.git/init/main.c
>> | > ===================================================================
>> | > --- linux-2.6.git.orig/init/main.c	2008-05-14 17:55:10.000000000 +0400
>> | > +++ linux-2.6.git/init/main.c	2008-05-14 19:11:18.000000000 +0400
>> | > @@ -702,7 +702,7 @@ static void __init do_initcalls(void)
>> | >
>> | >  	for (call = __initcall_start; call < __initcall_end; call++) {
>> | >  		ktime_t t0, t1, delta;
>> | > -		char msgbuf[40];
>> | > +		char msgbuf[64];
>> | >  		int result;
>> | >
>> | >  		if (initcall_debug) {
>> | > @@ -729,11 +729,11 @@ static void __init do_initcalls(void)
>> | >  			sprintf(msgbuf, "error code %d ", result);
>> | >
>> | >  		if (preempt_count() != count) {
>> | > -			strncat(msgbuf, "preemption imbalance ", sizeof(msgbuf));
>> | > +			strcat(msgbuf, "preemption imbalance ");
>> | >  			preempt_count() = count;
>> | >  		}
>> | >  		if (irqs_disabled()) {
>> | > -			strncat(msgbuf, "disabled interrupts ", sizeof(msgbuf));
>> | > +			strcat(msgbuf, "disabled interrupts ");
>> | >  			local_irq_enable();
>> | >  		}
>> | >  		if (msgbuf[0]) {
>> |
>> | umm, why can't m68k call strncat() from init/main.c??
>> |
>>
>> there some problem with headers iirc, we have to declare it first or
>> use some gcc option (as Adrian suggested). Actually I would prefer to use
>
> gcc turns the strncat() into an implicit call to strlen() and some form
> of expanded memcpy(). E.g.
>
>
> 	if (preempt_count() != count) {
> 		strncat(msgbuf, "preemption imbalance ", sizeof(msgbuf));
> 		preempt_count() = count;
> 	}
>
> becomes
>
>         cmp.l 884(%a2),%d6      | <variable>.thread.info.preempt_count,
> count
>         jeq .L61        |
>         move.l %d7,-(%sp)       | tmp76,
>         jbsr strlen     |
>         addq.l #4,%sp   |,
>         move.l %d7,%a0  | tmp76, tmp80
>         add.l %d0,%a0   |, tmp80
>         move.l #1886545253,(%a0)+       |,
>         move.l #1836086377,(%a0)+       |,
>         move.l #1869488233,(%a0)+       |,
>         move.l #1835164012,(%a0)+       |,
>         move.l #1634624357,(%a0)+       |,
>         move.w #8192,(%a0)      |,* D.28541
>         move.l %d6,884(%a2)     | count,
> <variable>.thread.info.preempt_count
> .L61:
>
> All other explicit calls to strlen() are inlined, as per
> include/asm-m68k/string.h.
>
>> strlcat there but it seems it would fail to build too. Originally I've
>> messed
>> strlcat with strncat :(
>
> Actually it build and runs fine after s/strncat/strlcat/...
>
> Gr{oetje,eeting}s,
>
> 						Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like
> that.
> 							    -- Linus Torvalds
>
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