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:

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"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/kern...

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.

-----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