From: Arnd Bergmann <arnd@arndb•de>
To: linuxppc-dev@lists•ozlabs.org
Cc: linuxppc-dev@ozlabs•org,
Andrew Morton <akpm@linux-foundation•org>,
Roel Kluin <roel.kluin@gmail•com>,
cbe-oss-dev@ozlabs•org
Subject: Re: [PATCH] powerpc/cell: strncpy does not null terminate string
Date: Fri, 17 Jul 2009 17:05:18 +0200 [thread overview]
Message-ID: <200907171705.18578.arnd@arndb.de> (raw)
In-Reply-To: <4A607185.6020302@gmail.com>
On Friday 17 July 2009, Roel Kluin wrote:
> With `sizeof(string) - 1` strncpy() will null terminate the string.
No, it won't. See the 'Warning' part of the strncpy man page.
> Signed-off-by: Roel Kluin <roel.kluin@gmail•com>
> ---
> To test this:
>
> #include <stdio.h>
> #include <string.h>
>
> char a[10];
> char b[10];
>
> int main()
> {
> const char* str = "0123456789012";
> strncpy(a, str, sizeof(a));
> strncpy(b, str, sizeof(b) - 1);
> printf("String a was %s, b was %s\n", a, b);
>
> return 0;
> }
>
> Output:
> String a was 0123456789012345678, b was 012345678
This is an invalid test case, it relies on b being zero-filled by the
compiler, which is not true for programs in general.
> diff --git a/arch/powerpc/platforms/cell/celleb_setup.c b/arch/powerpc/platforms/cell/celleb_setup.c
> index 07c234f..cfdbadb 100644
> --- a/arch/powerpc/platforms/cell/celleb_setup.c
> +++ b/arch/powerpc/platforms/cell/celleb_setup.c
> @@ -80,7 +80,7 @@ static void celleb_show_cpuinfo(struct seq_file *m)
>
> static int __init celleb_machine_type_hack(char *ptr)
> {
> - strncpy(celleb_machine_type, ptr, sizeof(celleb_machine_type));
> + strncpy(celleb_machine_type, ptr, sizeof(celleb_machine_type) - 1);
> celleb_machine_type[sizeof(celleb_machine_type)-1] = 0;
> return 0;
> }
See the line after the strncpy. This is still required for proper zero-termination.
Your patch tries to address a problem that doesn't exist, and does not have any
effect at all after celleb_machine_type_hack has completed.
Arnd <><
next prev parent reply other threads:[~2009-07-17 15:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-17 12:41 [PATCH] powerpc/cell: strncpy does not null terminate string Roel Kluin
2009-07-17 14:27 ` Roel Kluin
2009-07-17 15:56 ` Arnd Bergmann
2009-07-21 9:31 ` Ken Kawakami
2009-07-17 15:05 ` Arnd Bergmann [this message]
2009-07-17 15:19 ` roel kluin
2009-07-21 10:17 ` [PATCH] powerpc/cell: replace strncpy by strlcpy Roel Kluin
2009-07-22 4:22 ` Ken Kawakami
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