lkml.org 
[lkml]   [2012]   [Jan]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC] syscalls, x86: Add __NR_kcmp syscall
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.



\
 
 \ /
  Last update: 2012-01-20 15:55    [W:0.067 / U:1.488 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site