linux-kernel - Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external to a process (v7)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4B056791.5090002@gmail.com>
Date:	Thu, 19 Nov 2009 16:43:13 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, Neil Horman <nhorman@...driver.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	marcin.slusarz@...il.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external
 to a process (v7)

On 11/19/2009 12:15 AM, Oleg Nesterov wrote:
> On 11/18, Jiri Slaby wrote:
>>
>> On the last point: I added explicit ACCESS_ONCE all over there. If you
>> don't like I will trash it.
> 
> Just curious, why?
> 
> I mean, do you have any example of the "bad" behaviour which is
> fixed by ACCESS_ONCE() ?

Hi,

no, I haven't seen any errors caused by that yet. I added those in the
"just in case compiler starts to do weird things" manner.

>> The only remaining weird user is in
>> kernel/acct.c:
>>         /*
>>          * Accounting records are not subject to resource limits.
>>          */
>>         flim = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
>>         current->signal->rlim[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
>>         file->f_op->write(file, (char *)&ac,
>>                                sizeof(acct_t), &file->f_pos);
>>         current->signal->rlim[RLIMIT_FSIZE].rlim_cur = flim;
>>
>> It means that threads of the process with PACCT caps have unlimited file
>> size for a short while. If there is setrlimit in between, it gets wiped
>> out as well.
> 
> This is called when the whole thread-group exits, there are no
> live threads except current.

Not really, it is called from umount, sys_acct and other paths.

> At least, given that do_acct_process() does override_creds(), an
> ordinary user can't fool the accounting.

Agreed. That path can be executed only by a user with (at least) PACCT
or SYS_ADMIN caps. Hopefully.

Thanks.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/