Re: [RFC PATCH 5/6] selftests: Challenge RLIMIT_NPROC in user namespaces
From: Shuah Khan
Date: Wed Feb 09 2022 - 20:22:32 EST
On 2/7/22 5:17 AM, Michal Koutný wrote:
The services are started in descendant user namepaces, each of them
should honor the RLIMIT_NPROC that's passed during user namespace
creation.
main [user_ns_0]
` service [user_ns_1]
` worker 1
` worker 2
...
` worker k
...
` service [user_ns_n]
` worker 1
` worker 2
...
` worker k
Test uses explicit synchronization, to make sure original parent's limit
does not interfere with descendants.
Thank you for updating the test with the kernel updates. Please see
comments below. A bit of a concern with how long this test will run.
Did you time it?
Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
---
.../selftests/rlimits/rlimits-per-userns.c | 154 ++++++++++++++----
1 file changed, 125 insertions(+), 29 deletions(-)
diff --git a/tools/testing/selftests/rlimits/rlimits-per-userns.c b/tools/testing/selftests/rlimits/rlimits-per-userns.c
index 26dc949e93ea..54c1b345e42b 100644
--- a/tools/testing/selftests/rlimits/rlimits-per-userns.c
+++ b/tools/testing/selftests/rlimits/rlimits-per-userns.c
@@ -9,7 +9,9 @@
#include <sys/resource.h>
#include <sys/prctl.h>
#include <sys/stat.h>
+#include <sys/socket.h>
+#include <assert.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
@@ -21,38 +23,74 @@
#include <errno.h>
#include <err.h>
-#define NR_CHILDS 2
+#define THE_LIMIT 4
+#define NR_CHILDREN 5
+
+static_assert(NR_CHILDREN >= THE_LIMIT-1, "Need slots for limit-1 children.");
static char *service_prog;
static uid_t user = 60000;
static uid_t group = 60000;
+static struct rlimit saved_limit;
+
+/* Two uses: main and service */
+static pid_t child[NR_CHILDREN];
+static pid_t pid;
static void setrlimit_nproc(rlim_t n)
{
- pid_t pid = getpid();
struct rlimit limit = {
.rlim_cur = n,
.rlim_max = n
};
-
- warnx("(pid=%d): Setting RLIMIT_NPROC=%ld", pid, n);
+ if (getrlimit(RLIMIT_NPROC, &saved_limit) < 0)
+ err(EXIT_FAILURE, "(pid=%d): getrlimit(RLIMIT_NPROC)", pid);
if (setrlimit(RLIMIT_NPROC, &limit) < 0)
err(EXIT_FAILURE, "(pid=%d): setrlimit(RLIMIT_NPROC)", pid);
+
+ warnx("(pid=%d): Set RLIMIT_NPROC=%ld", pid, n);
+}
+
+static void restore_rlimit_nproc(void)
+{
+ if (setrlimit(RLIMIT_NPROC, &saved_limit) < 0)
+ err(EXIT_FAILURE, "(pid=%d): setrlimit(RLIMIT_NPROC, saved)", pid);
+ warnx("(pid=%d) Restored RLIMIT_NPROC", pid);
}
-static pid_t fork_child(void)
+enum msg_sync {
+ UNSHARE,
+ RLIMIT_RESTORE,
+};
+
+static void sync_notify(int fd, enum msg_sync m)
{
- pid_t pid = fork();
+ char tmp = m;
+
+ if (write(fd, &tmp, 1) < 0)
+ warnx("(pid=%d): failed sync-write", pid);
+}
- if (pid < 0)
+static void sync_wait(int fd, enum msg_sync m)
+{
+ char tmp;
+
+ if (read(fd, &tmp, 1) < 0)
+ warnx("(pid=%d): failed sync-read", pid);
+}
+
+static pid_t fork_child(int control_fd)
+{
+ pid_t new_pid = fork();
+
+ if (new_pid < 0)
err(EXIT_FAILURE, "fork");
- if (pid > 0)
- return pid;
+ if (new_pid > 0)
+ return new_pid;
pid = getpid();
-
warnx("(pid=%d): New process starting ...", pid);
if (prctl(PR_SET_PDEATHSIG, SIGKILL) < 0)
@@ -73,6 +111,9 @@ static pid_t fork_child(void)
if (unshare(CLONE_NEWUSER) < 0)
err(EXIT_FAILURE, "unshare(CLONE_NEWUSER)");
+ sync_notify(control_fd, UNSHARE);
+ sync_wait(control_fd, RLIMIT_RESTORE);
+
char *const argv[] = { "service", NULL };
char *const envp[] = { "I_AM_SERVICE=1", NULL };
@@ -82,37 +123,92 @@ static pid_t fork_child(void)
err(EXIT_FAILURE, "(pid=%d): execve", pid);
}
+static void run_service(void)
+{
+ size_t i;
+ int ret = EXIT_SUCCESS;
+ struct rlimit limit;
+ char user_ns[PATH_MAX];
+
+ if (getrlimit(RLIMIT_NPROC, &limit) < 0)
+ err(EXIT_FAILURE, "(pid=%d) failed getrlimit", pid);
+ if (readlink("/proc/self/ns/user", user_ns, PATH_MAX) < 0)
+ err(EXIT_FAILURE, "(pid=%d) failed readlink", pid);
+
+ warnx("(pid=%d) Service instance attempts %i children, limit %lu:%lu, ns=%s",
+ pid, THE_LIMIT, limit.rlim_cur, limit.rlim_max, user_ns);
+
+ /* test rlimit inside the service, effectively THE_LIMIT-1 becaue of service itself */
+ for (i = 0; i < THE_LIMIT; i++) {
+ child[i] = fork();
+ if (child[i] == 0) {
+ /* service child */
+ pause();
+ exit(EXIT_SUCCESS);
+ }
+ if (child[i] < 0) {
+ warnx("(pid=%d) service fork %lu failed, errno = %i", pid, i+1, errno);
+ if (!(i == THE_LIMIT-1 && errno == EAGAIN))
+ ret = EXIT_FAILURE;
+ } else if (i == THE_LIMIT-1) {
+ warnx("(pid=%d) RLIMIT_NPROC not honored", pid);
+ ret = EXIT_FAILURE;
+ }
+ }
+
+ /* service cleanup */
+ for (i = 0; i < THE_LIMIT; i++)
+ if (child[i] > 0)
+ kill(child[i], SIGUSR1);
+
+ for (i = 0; i < THE_LIMIT; i++)
+ if (child[i] > 0)
+ waitpid(child[i], NULL, WNOHANG);
+
+ if (ret)
+ exit(ret);
+ pause();
+}
+
int main(int argc, char **argv)
{
size_t i;
- pid_t child[NR_CHILDS];
- int wstatus[NR_CHILDS];
- int childs = NR_CHILDS;
- pid_t pid;
+ int control_fd[NR_CHILDREN];
+ int wstatus[NR_CHILDREN];
+ int children = NR_CHILDREN;
+ int sockets[2];
+
+ pid = getpid();
if (getenv("I_AM_SERVICE")) {
- pause();
- exit(EXIT_SUCCESS);
+ run_service();
+ exit(EXIT_FAILURE);
Why is this a failure unconditionally?
}
service_prog = argv[0];
- pid = getpid();
warnx("(pid=%d) Starting testcase", pid);
- /*
- * This rlimit is not a problem for root because it can be exceeded.
- */
- setrlimit_nproc(1);
-
- for (i = 0; i < NR_CHILDS; i++) {
- child[i] = fork_child();
+ setrlimit_nproc(THE_LIMIT);
+ for (i = 0; i < NR_CHILDREN; i++) {
+ if (socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0, sockets) < 0)
+ err(EXIT_FAILURE, "(pid=%d) socketpair failed", pid);
+ control_fd[i] = sockets[0];
+ child[i] = fork_child(sockets[1]);
wstatus[i] = 0;
+ }
+
+ for (i = 0; i < NR_CHILDREN; i++)
+ sync_wait(control_fd[i], UNSHARE);
+ restore_rlimit_nproc();
+
+ for (i = 0; i < NR_CHILDREN; i++) {
+ sync_notify(control_fd[i], RLIMIT_RESTORE);
usleep(250000);
How long does this test now run for with this loop?
}
while (1) {
- for (i = 0; i < NR_CHILDS; i++) {
+ for (i = 0; i < NR_CHILDREN; i++) {
if (child[i] <= 0)
continue;
@@ -126,22 +222,22 @@ int main(int argc, char **argv)
warn("(pid=%d): waitpid(%d)", pid, child[i]);
child[i] *= -1;
- childs -= 1;
+ children -= 1;
}
- if (!childs)
+ if (!children)
break;
usleep(250000);
- for (i = 0; i < NR_CHILDS; i++) {
+ for (i = 0; i < NR_CHILDREN; i++) {
if (child[i] <= 0)
continue;
kill(child[i], SIGUSR1);
}
}
- for (i = 0; i < NR_CHILDS; i++) {
+ for (i = 0; i < NR_CHILDREN; i++) {
if (WIFEXITED(wstatus[i]))
warnx("(pid=%d): pid %d exited, status=%d",
pid, -child[i], WEXITSTATUS(wstatus[i]));
Please a add few more comments in the code path.
thanks,
-- Shuah