linux-kernel - Re: [PATCH 1/6] POWERPC: use KSYM_NAME

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Date:	Wed, 23 Jan 2008 18:26:28 +0000
From:	Paulo Marques <pmarques@...popie.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/6] POWERPC: use KSYM_NAME_LEN

Cyrill Gorcunov wrote:
> Use KSYM_NAME_LEN instead of numeric value.

The patch series looks like a nice cleanup, except for a few things in 
this patch.

> Actually because of too small 'tmp' there is
> a potential buffer overflow.

I don't think there is. "tmp" is not being passed to kallsyms to be 
filled with a symbol name, but it's being used to hold a name written by 
the user to lookup an address.

If the powerpc/xmon people feel that 63 characters is enough to hold a 
symbol name, it's their problem, but there is no buffer overflow.

> Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
> ---
> 
> Index: linux-2.6.git/arch/powerpc/xmon/xmon.c
> ===================================================================
> --- linux-2.6.git.orig/arch/powerpc/xmon/xmon.c	2008-01-23 19:04:42.000000000 +0300
> +++ linux-2.6.git/arch/powerpc/xmon/xmon.c	2008-01-23 19:12:45.000000000 +0300
> @@ -69,7 +69,7 @@ static unsigned long ndump = 64;
>  static unsigned long nidump = 16;
>  static unsigned long ncsum = 4096;
>  static int termch;
> -static char tmpstr[128];
> +static char tmpstr[KSYM_NAME_LEN];

This one seems ok, since "tmpstr" is used everywhere to hold symbol names.

>  #define JMP_BUF_LEN	23
>  static long bus_error_jmp[JMP_BUF_LEN];
> @@ -2354,7 +2354,7 @@ scanhex(unsigned long *vp)
>  		}
>  	} else if (c == '$') {
>  		int i;
> -		for (i=0; i<63; i++) {
> +		for (i = 0; i < sizeof(tmpstr) / 2; i++) {

This one is completely out of the blue. Why "sizeof(tmpstr) / 2"?

It would make more sense to use "sizeof(tmpstr) - 1", but either way it 
is a change in behavior.

>  			c = inchar();
>  			if (isspace(c)) {
>  				termch = c;
> @@ -2467,7 +2467,7 @@ symbol_lookup(void)
>  {
>  	int type = inchar();
>  	unsigned long addr;
> -	static char tmp[64];
> +	static char tmp[KSYM_NAME_LEN];
>  
>  	switch (type) {
>  	case 'a':
> @@ -2476,7 +2476,7 @@ symbol_lookup(void)
>  		termch = 0;
>  		break;
>  	case 's':
> -		getstring(tmp, 64);
> +		getstring(tmp, sizeof(tmp));
>  		if (setjmp(bus_error_jmp) == 0) {
>  			catch_memory_errors = 1;
>  			sync();

This also introduces a change in behavior. It is still a nice cleanup, 
though. So, if the powerpc people feel they can spare an extra 64 bytes 
of stack here, I guess it's ok.

-- 
Paulo Marques - www.grupopie.com

"As far as we know, our computer has never had an undetected error."
Weisert
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