From: "H. Peter Anvin" <hpa@zytor.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Pavel Emelyanov <xemul@parallels.com>,
KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
david@lang.hm, Alexey Dobriyan <adobriyan@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Andrey Vagin <avagin@openvz.org>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>,
Glauber Costa <glommer@parallels.com>,
Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
Matt Helsley <matthltc@us.ibm.com>,
Pekka Enberg <penberg@kernel.org>,
Eric Dumazet <eric.dumazet@gmail.com>,
Vasiliy Kulikov <segoon@openwall.com>,
Andrew Morton <akpm@linux-foundation.org>,
Valdis.Kletnieks@vt.edu
Subject: Re: [RFC] syscalls, x86: Add __NR_kcmp syscall
Date: Fri, 20 Jan 2012 06:51:31 -0800 [thread overview]
Message-ID: <4F197F73.3010000@zytor.com> (raw)
In-Reply-To: <20120120090225.GD2786@moon>
On 01/20/2012 01:02 AM, Cyrill Gorcunov wrote:
> On Fri, Jan 20, 2012 at 12:40:08PM +0400, Cyrill Gorcunov wrote:
> ...
>> +
>> +static __init int kcmp_cookie_init(void)
>> +{
>> + int i, j;
>> +
>> + for (i = 0; i < KCMP_TYPES; i++) {
>> + for (j = 0; j < 2; j++) {
>> + get_random_bytes(&cookies[i][j], sizeof(cookies[i][j]));
>> +
>> + if (cookies[i][j])
>> + continue;
>> +
>> + /*
>> + * This is impossible case but just to be sure.
>> + */
>> + cookies_valid = false;
>> + WARN_ONCE(1, "Can't get random bytes for k-pointers\n");
>> + }
>> + }
>> +
>> + cookies_valid = true;
>
> darn, this string of course should be on top,
> i'll update don't complain on this nit.
>
This code is wrong. You will have a zero cookie, legitimately, once in
2^32 or 2^64 attempts, depending on the bitness.
The other thing is that for the multiplicative cookie you should OR in
the value (~(~0UL >> 1) | 1) in order to make sure that the value is (a)
large and (b) odd.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2012-01-20 14:52 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-17 14:27 [RFC] syscalls, x86: Add __NR_kcmp syscall Cyrill Gorcunov
2012-01-17 14:38 ` Alexey Dobriyan
2012-01-17 14:44 ` Cyrill Gorcunov
2012-01-17 18:47 ` H. Peter Anvin
2012-01-17 21:15 ` Cyrill Gorcunov
2012-01-17 21:40 ` Eric W. Biederman
2012-01-18 5:07 ` Pavel Emelyanov
2012-01-17 21:35 ` Eric W. Biederman
2012-01-18 8:01 ` Cyrill Gorcunov
2012-01-18 9:12 ` KOSAKI Motohiro
2012-01-18 9:19 ` Pavel Emelyanov
2012-01-18 9:23 ` KOSAKI Motohiro
2012-01-18 11:57 ` Cyrill Gorcunov
2012-01-18 16:46 ` KOSAKI Motohiro
2012-01-18 17:20 ` Cyrill Gorcunov
2012-01-18 22:05 ` david
2012-01-18 22:49 ` Cyrill Gorcunov
2012-01-18 23:29 ` Eric W. Biederman
2012-01-19 6:55 ` Cyrill Gorcunov
2012-01-20 3:16 ` Eric W. Biederman
2012-01-20 8:40 ` Cyrill Gorcunov
2012-01-20 9:02 ` Cyrill Gorcunov
2012-01-20 14:51 ` H. Peter Anvin [this message]
2012-01-20 16:29 ` Cyrill Gorcunov
2012-01-20 16:57 ` H. Peter Anvin
2012-01-20 18:19 ` Cyrill Gorcunov
2012-01-20 18:22 ` Cyrill Gorcunov
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