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List:       kernel-hardening
Subject:    Re: [PATCH v11 5/9] Reimplement RLIMIT_MSGQUEUE on top of ucounts
From:       Alexey Gladkov <legion () kernel ! org>
Date:       2021-08-19 17:26:18
Message-ID: 20210819172618.qwrrw4m7wt33wfmz () example ! org
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On Thu, Aug 19, 2021 at 10:10:26AM -0500, Eric W. Biederman wrote:
> Alexey Gladkov <legion@kernel.org> writes:
> 
> > On Tue, Aug 17, 2021 at 10:47:14AM -0500, Eric W. Biederman wrote:
> > > "Ma, XinjianX" <xinjianx.ma@intel.com> writes:
> > > 
> > > > Hi Alexey,
> > > > 
> > > > When lkp team run kernel selftests, we found after these series of patches, \
> > > > testcase mqueue: mq_perf_tests in kselftest failed with following message.
> > > 
> > > Which kernel was this run against?
> > > 
> > > Where can the mq_perf_tests that you ran and had problems with be found?
> > > 
> > > During your run were you using user namespaces as part of your test
> > > environment?
> > > 
> > > The error message too many files corresponds to the error code EMFILES
> > > which is the error code that is returned when the rlimit is reached.
> > > 
> > > One possibility is that your test environment was run in a user
> > > namespace and so you wound up limited by rlimit of the user who created
> > > the user namespace at the point of user namespace creation. 
> > > 
> > > At this point if you can give us enough information to look into this
> > > and attempt to reproduce it that would be appreciated.
> > 
> > I was able to reproduce it on master without using user namespace.
> > I suspect that the maximum value is not assigned here [1]:
> > 
> > set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE, \
> > task_rlimit(&init_task, RLIMIT_MSGQUEUE)); 
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/fork.c#n832
> > 
> 
> The rlimits for init_task are set to INIT_RLIMITS.
> In INIT_RLIMITS RLIMIT_MSGQUEUE is set to MQ_MAX_BYTES
> 
> So that definitely means that as the code is current constructed the
> rlimit can not be effectively raised.
> 
> So it looks like we are just silly and preventing the initial rlimits
> from being raised.
> 
> So we probably want to do something like:

Damn, you are faster than me! :)

> diff --git a/kernel/fork.c b/kernel/fork.c
> index bc94b2cc5995..557ce0083ba3 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -825,13 +825,13 @@ void __init fork_init(void)
> 	init_task.signal->rlim[RLIMIT_SIGPENDING] =
> 		init_task.signal->rlim[RLIMIT_NPROC];
> 
> +	/* For non-rlimit ucounts make their default limit max_threads/2 */
> 	for (i = 0; i < MAX_PER_NAMESPACE_UCOUNTS; i++)
> 		init_user_ns.ucount_max[i] = max_threads/2;
> 
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_NPROC, task_rlimit(&init_task, \
>                 RLIMIT_NPROC));
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE, \
>                 task_rlimit(&init_task, RLIMIT_MSGQUEUE));
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_SIGPENDING, \
>                 task_rlimit(&init_task, RLIMIT_SIGPENDING));
> -	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MEMLOCK, \
> task_rlimit(&init_task, RLIMIT_MEMLOCK)); +	/* In init_user_ns default rlimit to be \
> the only limit */ +	for (; i < UCOUNT_COUNTS; i++)
> +		set_rlimit_ucount_max(&init_user_ns, i, RLIMIT_INFINITY);

s/RLIMIT_INFINITY/RLIM_INFINITY/

> 
> #ifdef CONFIG_VMAP_STACK
> 	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
> 

Acked-by: Alexey Gladkov <legion@kernel.org>

I cannot complete this test on my laptop. On 4Gb, the test ends with
oom-killer. But with this patch, the test definitely passes the moment of
the previous fall.

-- 
Rgrds, legion


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