linux-kernel - Re: [PATCH] seccomp: do not reject initial filter using TSYNC

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Message-ID: <CAGXu5j+d38Uy=Rwjrt4NFjEgWZ13djFdF_RWHVPKAMnDn9YTVw@mail.gmail.com>
Date:	Thu, 17 Jul 2014 10:56:36 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	Oleg Nesterov <oleg@...hat.com>,
	David Drysdale <drysdale@...gle.com>
Subject: Re: [PATCH] seccomp: do not reject initial filter using TSYNC

On Thu, Jul 17, 2014 at 10:53 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Thu, Jul 17, 2014 at 10:49 AM, Kees Cook <keescook@...omium.org> wrote:
>> There was an unneeded sanity check in the TSYNC code that was causing
>> the first filter applied to not allow the TSYNC flag. Additionally,
>> this optimizes the thread loops to skip "current". It was harmless, but
>> better to not cause problems in the future.
>>
>> Reported-by: David Drysdale <drysdale@...gle.com>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>> This goes on top of the v11 seccomp-tsync series. If I should respin
>> as v12, please let me know.
>>
>> Thanks!
>> ---
>>  kernel/seccomp.c |   11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>> index 2125b83ccfd4..0e0c6905b81d 100644
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -255,14 +255,15 @@ static inline pid_t seccomp_can_sync_threads(void)
>>         BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
>>         BUG_ON(!spin_is_locked(&current->sighand->siglock));
>>
>> -       if (current->seccomp.mode != SECCOMP_MODE_FILTER)
>> -               return -EACCES;
>> -
>>         /* Validate all threads being eligible for synchronization. */
>>         caller = current;
>>         for_each_thread(caller, thread) {
>>                 pid_t failed;
>>
>> +               /* Skip current, since it is initiating the sync. */
>> +               if (thread == current)
>> +                       continue;
>> +
>
> Should that be "thread == caller"?

caller shouldn't be changing, correct? Won't it be the same?

-Kees

-- 
Kees Cook
Chrome OS Security
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