Note that in its final form this isn’t had any testing on an Ubuntu machine, so 
testing would be appreciated if anyone has an Ubuntu 24.x machine (not a 
container, need their kernel) with apparmor enabled.

Thanks,
Ross

> On 12 Sep 2024, at 17:57, Ross Burton via lists.openembedded.org 
> <[email protected]> wrote:
> 
> If user namespaces are not available (typically because AppArmor is
> blocking them), alert the user.
> 
> We consider network isolation sufficiently important that this is a fatal
> error, and the user will need to configure AppArmor to allow bitbake to
> create a user namespace.
> 
> [ YOCTO #15592 ]
> 
> Signed-off-by: Ross Burton <[email protected]>
> ---
> meta/classes-global/sanity.bbclass | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
> 
> diff --git a/meta/classes-global/sanity.bbclass 
> b/meta/classes-global/sanity.bbclass
> index 1d242f0f0a0..72dab0fea2b 100644
> --- a/meta/classes-global/sanity.bbclass
> +++ b/meta/classes-global/sanity.bbclass
> @@ -475,6 +475,29 @@ def check_wsl(d):
>             bb.warn("You are running bitbake under WSLv2, this works properly 
> but you should optimize your VHDX file eventually to avoid running out of 
> storage space")
>     return None
> 
> +def check_userns():
> +    """
> +    Check that user namespaces are functional, as they're used for network 
> isolation.
> +    """
> +
> +    # There is a known failure case with AppAmrmor where the unshare() call
> +    # succeeds (at which point the uid is nobody) but writing to the uid_map
> +    # fails (so the uid isn't reset back to the user's uid). We can detect 
> this.
> +    parentuid = os.getuid()
> +    pid = os.fork()
> +    if not pid:
> +        try:
> +            bb.utils.disable_network()
> +        except:
> +            pass
> +        os._exit(parentuid != os.getuid())
> +
> +    ret = os.waitpid(pid, 0)[1]
> +    if ret:
> +        bb.fatal("User namespaces are not usable by BitBake, possibly due to 
> AppArmor.\n"
> +                 "See 
> https://discourse.ubuntu.com/t/ubuntu-24-04-lts-noble-numbat-release-notes/39890#unprivileged-user-namespace-restrictions
>  for more information.")
> +
> +
> # Require at least gcc version 8.0
> #
> # This can be fixed on CentOS-7 with devtoolset-6+
> @@ -641,6 +664,7 @@ def check_sanity_version_change(status, d):
>     status.addresult(check_git_version(d))
>     status.addresult(check_perl_modules(d))
>     status.addresult(check_wsl(d))
> +    status.addresult(check_userns())
> 
>     missing = ""
> 
> -- 
> 2.34.1
> 
> 
> 
> 

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