RE: [PATCH] ucounts: Fix regression preventing increasing of rlimits in init_user_ns

["Ma, XinjianX" <xinjianx.ma@intel.com>]

> -----Original Message-----
> From: Eric W. Biederman <ebiederm@xmission.com>
> Sent: Tuesday, August 24, 2021 5:07 AM
> To: Alexey Gladkov <legion@kernel.org>
> Cc: Ma, XinjianX <xinjianx.ma@intel.com>; linux-kselftest@vger.kernel.org;
> lkp <lkp@intel.com>; akpm@linux-foundation.org; axboe@kernel.dk;
> christian.brauner@ubuntu.com; containers@lists.linux-foundation.org;
> jannh@google.com; keescook@chromium.org; kernel-
> hardening@lists.openwall.com; linux-kernel@vger.kernel.org; linux-
> mm@kvack.org; oleg@redhat.com; torvalds@linux-foundation.org
> Subject: [PATCH] ucounts: Fix regression preventing increasing of rlimits in
> init_user_ns
> 
> 
> "Ma, XinjianX" <xinjianx.ma@intel.com> reported:
> 
> > When lkp team run kernel selftests, we found after these series of
> > patches, testcase mqueue: mq_perf_tests in kselftest failed with following
> message.
> >
> > # selftests: mqueue: mq_perf_tests
> > #
> > # Initial system state:
> > #       Using queue path:                       /mq_perf_tests
> > #       RLIMIT_MSGQUEUE(soft):                  819200
> > #       RLIMIT_MSGQUEUE(hard):                  819200
> > #       Maximum Message Size:                   8192
> > #       Maximum Queue Size:                     10
> > #       Nice value:                             0
> > #
> > # Adjusted system state for testing:
> > #       RLIMIT_MSGQUEUE(soft):                  (unlimited)
> > #       RLIMIT_MSGQUEUE(hard):                  (unlimited)
> > #       Maximum Message Size:                   16777216
> > #       Maximum Queue Size:                     65530
> > #       Nice value:                             -20
> > #       Continuous mode:                        (disabled)
> > #       CPUs to pin:                            3
> > # ./mq_perf_tests: mq_open() at 296: Too many open files not ok 2
> > selftests: mqueue: mq_perf_tests # exit=1 ```
> >
> > Test env:
> > rootfs: debian-10
> > gcc version: 9
> 
> After investigation the problem turned out to be that ucount_max for the
> rlimits in init_user_ns was being set to the initial rlimit value.
> The practical problem is that ucount_max provides a limit that applications
> inside the user namespace can not exceed.  Which means in practice that
> rlimits that have been converted to use the ucount infrastructure were not
> able to exceend their initial rlimits.
> 
> Solve this by setting the relevant values of ucount_max to RLIM_INIFINITY.  A
> limit in init_user_ns is pointless so the code should allow the values to grow
> as large as possible without riscking an underflow or an overflow.
> 
> As the ltp test case was a bit of a pain I have reproduced the rlimit failure and
> tested the fix with the following little C program:
> > #include <stdio.h>
> > #include <fcntl.h>
> > #include <sys/stat.h>
> > #include <mqueue.h>
> > #include <sys/time.h>
> > #include <sys/resource.h>
> > #include <errno.h>
> > #include <string.h>
> > #include <stdlib.h>
> > #include <limits.h>
> > #include <unistd.h>
> >
> > int main(int argc, char **argv)
> > {
> > 	struct mq_attr mq_attr;
> > 	struct rlimit rlim;
> > 	mqd_t mqd;
> > 	int ret;
> >
> > 	ret = getrlimit(RLIMIT_MSGQUEUE, &rlim);
> > 	if (ret != 0) {
> > 		fprintf(stderr, "getrlimit(RLIMIT_MSGQUEUE) failed: %s\n",
> strerror(errno));
> > 		exit(EXIT_FAILURE);
> > 	}
> > 	printf("RLIMIT_MSGQUEUE %lu %lu\n",
> > 	       rlim.rlim_cur, rlim.rlim_max);
> > 	rlim.rlim_cur = RLIM_INFINITY;
> > 	rlim.rlim_max = RLIM_INFINITY;
> > 	ret = setrlimit(RLIMIT_MSGQUEUE, &rlim);
> > 	if (ret != 0) {
> > 		fprintf(stderr, "setrlimit(RLIMIT_MSGQUEUE, RLIM_INFINITY)
> failed: %s\n", strerror(errno));
> > 		exit(EXIT_FAILURE);
> > 	}
> >
> > 	memset(&mq_attr, 0, sizeof(struct mq_attr));
> > 	mq_attr.mq_maxmsg = 65536 - 1;
> > 	mq_attr.mq_msgsize = 16*1024*1024 - 1;
> >
> > 	mqd = mq_open("/mq_rlimit_test", O_RDONLY|O_CREAT, 0600,
> &mq_attr);
> > 	if (mqd == (mqd_t)-1) {
> > 		fprintf(stderr, "mq_open failed: %s\n", strerror(errno));
> > 		exit(EXIT_FAILURE);
> > 	}
> > 	ret = mq_close(mqd);
> > 	if (ret) {
> > 		fprintf(stderr, "mq_close failed; %s\n", strerror(errno));
> > 		exit(EXIT_FAILURE);
> > 	}
> >
> > 	return EXIT_SUCCESS;
> > }
> 
> Fixes: 6e52a9f0532f ("Reimplement RLIMIT_MSGQUEUE on top of ucounts")
> Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
> Fixes: d64696905554 ("Reimplement RLIMIT_SIGPENDING on top of ucounts")
> Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
> Reported-by: kernel test robot lkp@intel.com
Sorry, but <> around email address is needed 
Reported-by: kernel test robot <lkp@intel.com>

> Acked-by: Alexey Gladkov <legion@kernel.org>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> 
> This is a simplified version of my previous change that I have tested and will
> push out to linux-next and then to Linus shortly.
> 
>  kernel/fork.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c index bc94b2cc5995..44f4c2d83763
> 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -828,10 +828,10 @@ void __init fork_init(void)
>  	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));
> +	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_NPROC,
> RLIM_INFINITY);
> +	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE,
> RLIM_INFINITY);
> +	set_rlimit_ucount_max(&init_user_ns,
> UCOUNT_RLIMIT_SIGPENDING, RLIM_INFINITY);
> +	set_rlimit_ucount_max(&init_user_ns, UCOUNT_RLIMIT_MEMLOCK,
> RLIM_INFINITY);
> 
>  #ifdef CONFIG_VMAP_STACK
>  	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN,
> "fork:vm_stack_cache",
> --
> 2.20.1