linux-kernel - Re: [PATCH v7 7/9] seccomp: implement SECCOMP_FILTER_FLAG

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <CAGXu5jKoDEXffJqFSjhO+D=5toJOA=KAomi+LQOahPDYKFbEdg@mail.gmail.com>
Date:	Tue, 24 Jun 2014 11:05:22 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Will Drewry <wad@...omium.org>,
	Julien Tinnes <jln@...omium.org>,
	David Drysdale <drysdale@...gle.com>,
	Linux API <linux-api@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-mips@...ux-mips.org,
	linux-arch <linux-arch@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v7 7/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC

On Tue, Jun 24, 2014 at 10:27 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 06/23, Kees Cook wrote:
>>
>> +static pid_t seccomp_can_sync_threads(void)
>> +{
>> +     struct task_struct *thread, *caller;
>> +
>> +     BUG_ON(write_can_lock(&tasklist_lock));
>> +     BUG_ON(!spin_is_locked(&current->sighand->siglock));
>> +
>> +     if (current->seccomp.mode != SECCOMP_MODE_FILTER)
>> +             return -EACCES;
>> +
>> +     /* Validate all threads being eligible for synchronization. */
>> +     thread = caller = current;
>> +     for_each_thread(caller, thread) {
>> +             pid_t failed;
>> +
>> +             if (thread->seccomp.mode == SECCOMP_MODE_DISABLED ||
>> +                 (thread->seccomp.mode == SECCOMP_MODE_FILTER &&
>> +                  is_ancestor(thread->seccomp.filter,
>> +                              caller->seccomp.filter)))
>> +                     continue;
>> +
>> +             /* Return the first thread that cannot be synchronized. */
>> +             failed = task_pid_vnr(thread);
>> +             /* If the pid cannot be resolved, then return -ESRCH */
>> +             if (failed == 0)
>> +                     failed = -ESRCH;
>
> forgot to mention, task_pid_vnr() can't fail. sighand->siglock is held,
> for_each_thread() can't see a thread which has passed unhash_process().

Certainly good to know, but I'd be much more comfortable leaving this
check as-is. Having "failed" return with "0" would be very very bad
(userspace would think the filter had been successfully applied, etc).
I'd rather stay highly defensive here.

-Kees

-- 
Kees Cook
Chrome OS Security
--
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/