[PATCH] fix create thread failed in unprivileged process [BZ #28287]

[Hongxu Jia <hongxu.jia@windriver.com>]

Since commit [d8ea0d0168 Add an internal wrapper for clone, clone2 and clone3]
applied, start a unprivileged container (docker run without --privileged),
it creates a thread failed in container.

In commit d8ea0d0168, it calls __clone3 if HAVE_CLONE3_WAPPER is defined.  If
__clone3 returns -1 with ENOSYS, fall back to clone or clone2.

As known from [1], cloneXXX fails with EPERM if CLONE_NEWCGROUP,
CLONE_NEWIPC, CLONE_NEWNET, CLONE_NEWNS, CLONE_NEWPID, or CLONE_NEWUTS
was specified by an unprivileged process (process without CAP_SYS_ADMIN)

[1] https://man7.org/linux/man-pages/man2/clone3.2.html

So if __clone3 returns -1 with EPERM, fall back to clone or clone2 could
fix the issue. Here are the test steps:

1) Prepare test code
cat > conftest.c <<ENDOF
 #include <pthread.h>
 #include <stdio.h>

int check_me = 0;
void* func(void* data) {check_me = 42; printf("start thread: check_me %d\n", check_me); return &check_me;}
int main()
{
  pthread_t t;
  void *ret;
  pthread_create (&t, 0, func, 0);
  pthread_join (t, &ret);
  printf("check_me %d, p %p\n", check_me, &ret);
  return (check_me != 42 || ret != &check_me);
}

ENDOF

2) Compile
gcc -o conftest -pthread conftest.c

3) Start a container with glibc 2.34 installed
[skip details]
docker run -it <container-image-name> bash

4) Run conftest without this patch
$ ./conftest
check_me 0, p 0x7ffd91ccd400

5) Run conftest with this patch
$ ./conftest
start thread: check_me 42
check_me 42, p 0x7ffe253c6f20

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
---
 sysdeps/unix/sysv/linux/clone-internal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/unix/sysv/linux/clone-internal.c b/sysdeps/unix/sysv/linux/clone-internal.c
index 979f7880be..97101994e8 100644
--- a/sysdeps/unix/sysv/linux/clone-internal.c
+++ b/sysdeps/unix/sysv/linux/clone-internal.c
@@ -52,7 +52,7 @@ __clone_internal (struct clone_args *cl_args,
   /* Try clone3 first.  */
   int saved_errno = errno;
   ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
-  if (ret != -1 || errno != ENOSYS)
+  if (ret != -1 || (errno != ENOSYS && errno != EPERM))
     return ret;
 
   /* NB: Restore errno since errno may be checked against non-zero
-- 
2.30.2