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

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Message-ID: <Pine.LNX.4.64.0805152132530.22059@anakin>
Date:	Thu, 15 May 2008 21:47:26 +0200 (CEST)
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
cc:	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

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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