add stressors for recursive mounts

[Seth Arnold]

I saw an interesting exchange on LKML the other day about user namespaces then allowing users to perform mounts, leading to unbounded kernel memory use:

http://marc.info/?l=linux-kernel&m=145349682207690&w=2

"what you are doing is essentially mount --rbind / / in infinite
loop in luserns. Which ends up eating all memory."

http://marc.info/?l=linux-kernel&m=145349772807910&w=2

This might be a useful direction to take stress-ng if it doesn't already perform unprivileged user mounts.

Thanks

[Colin Ian King (colin-king)]

I got the reproducer down to the following minimal code:

#define _GNU_SOURCE
#include <unistd.h>
#include <sched.h>
#include <sys/wait.h>
#include <sys/mount.h>

int loop(void *arg)
{
        for (;;)
            mount("/", "/", "", MS_BIND | MS_REC, 0);
        return 0;
}

int main()
{
        int pid, status;
        char stack[65536];

        pid = clone(loop, &stack[sizeof(stack)-8], CLONE_NEWUSER | CLONE_NEWNS | CLONE_NEWPID, 0, 0);
        while (waitpid(pid, &status, __WALL) != pid);
        return 0;
}

[Colin Ian King (colin-king)]

Fix committed, http://kernel.ubuntu.com/git/cking/stress-ng.git/commit/?id=d36ea96fe7b4def36cea9fb1fe52ca18ee94bfa1

[Launchpad Janitor (janitor)]

This bug was fixed in the package stress-ng - 0.05.14-1

---------------
stress-ng (0.05.14-1) unstable; urgency=medium

  * Makefile: bump version
  * Fix make dist - typo in test-libpthread.c
  * stress-fiemap: initialise counter at start of loop
  * stress-fiemap: ensure counter is being updated
  * adt: exclude bind mount from list of stressors
  * Don't emit warning on --pathological if number of stressors is zero
  * ignite-cpu: add null entry at end of list, don't scan by array size
  * Only include <sys/mount.h> for linux for the bind mount stressor
  * stress-bind-mount: build stressor if STRESS_BIND_MOUNT defined
  * stress-bind-mount: stop cppcheck whining about uninitialised pid
  * stress-numa: don't fatally fail on -EIO with MPOL_MF_STRICT (LP: #1542741)
  * Enabled IGNITE_CPU with the --aggressive option
  * Add bind-mount stressor (LP: #1542010)
  * Add --ignite-cpu option to maximize CPU frequency
  * Make float decimal auto detect set -DHAVE_FLOAT_DECIMAL
  * Minor re-org of Makefile, and add more files to dist rule
  * Update README - increase number of stressors
  * adt tests: remove membarrier, it fails on older kernels in Debian
  * Add some more comments
  * stress-affinity: handle EINVAL when CPU(s) are offline
  * Set number of instances to on-line CPUs if N is -ve (LP: #1513546)
  * Remove opt_long, replace with get_int32 or get_uint64
  * Add libpthread build time checks
  * Add librt build time checks
  * Remove commented out old link line
  * Add libcrypt check
  * Makefile: remove test-libz correctly
  * stress-cpu: make source 80 column friendly
  * Add FORCE_DO_NOTHING macro do force compiler to stop opimizing out loops
  * Add zlib stressor
  * stress-stream: cater for systems without L3 cache
  * stress-stream: only emit cache size info on instance 0
  * Add libbsd-dev to README

 -- Colin King <email address hidden> Mon, 8 Feb 2016 18:29:11 +0000