Re: [PATCH] fs/pidfs: when time ns disabled add check for ioctl

[Christian Brauner]

On Sun, Jul 21, 2024 at 02:23:12PM GMT, Edward Adam Davis wrote:
> syzbot call pidfd_ioctl() with cmd "PIDFD_GET_TIME_NAMESPACE" and disabled
> CONFIG_TIME_NS, since time_ns is NULL, it will make NULL ponter deref in
> open_namespace.
> 
> Reported-and-tested-by: syzbot+34a0ee986f61f15da35d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=34a0ee986f61f15da35d
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> ---

Hm, nsproxy is really messy in that regard. Some namespaces will always
be set to init_<type>_ns and others will be set to NULL.

That's an invitation for bugs such as this. Imho the correct fix is to
change nsproxy to always set nsp-><type>_ns to init_<type>_ns and no
code ever needs to worry about dereferencing NULL.

But that'll require more changes so this seems an appropriate fix for now.