RFC: Disable clone3 for glibc 2.34

[Florian Weimer]

* Florian Weimer via Libc-alpha:

> Reportedly, the docker package in Ubuntu as used by Github Actions and
> others does not provide a way to enable the clone3 system call.  It
> always fails with EPERM.
>
> Should we apply a patch like this for the release?
>
> diff --git a/sysdeps/unix/sysv/linux/clone-internal.c b/sysdeps/unix/sysv/linux/clone-internal.c
> index 1e7a8f6b35..4046c81180 100644
> --- a/sysdeps/unix/sysv/linux/clone-internal.c
> +++ b/sysdeps/unix/sysv/linux/clone-internal.c
> @@ -48,17 +48,6 @@ __clone_internal (struct clone_args *cl_args,
>  		  int (*func) (void *arg), void *arg)
>  {
>    int ret;
> -#ifdef HAVE_CLONE3_WAPPER
> -  /* Try clone3 first.  */
> -  int saved_errno = errno;
> -  ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
> -  if (ret != -1 || errno != ENOSYS)
> -    return ret;
> -
> -  /* NB: Restore errno since errno may be checked against non-zero
> -     return value.  */
> -  __set_errno (saved_errno);
> -#endif
>  
>    /* Map clone3 arguments to clone arguments.  NB: No need to check
>       invalid clone3 specific bits in flags nor exit_signal since this
>
> My concern with this is that we don't know yet where the CET kernel API
> will land exactly and if CET will require clone3.  So clone3 might have
> to come back once we turn on CET, which is hopefully soon.

Ubuntu 20.04 LTS may have already been fixed, I cannot reproduce the
issue with its docker.io/containerd/runc packages.

I could trivially fix a previously failing Github Action with:

diff --git a/.github/workflows/fedora.yml b/.github/workflows/fedora.yml
index d2381ec..7b10286 100644
--- a/.github/workflows/fedora.yml
+++ b/.github/workflows/fedora.yml
@@ -22,6 +22,7 @@ jobs:
     runs-on: ubuntu-latest
     container:
       image: fedora:${{matrix.release}}
+      options: --security-opt seccomp=unconfined
 
     steps:
       - name: Checkout repository

So I think we need to figure out what people are actually complaining
about.

Thanks,
Florian