Re: [PATCH 1/3] init/main.c: introduce function ramdisk_exec_exist()

[Menglong Dong]

On Tue, May 25, 2021 at 11:43 AM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
>
> On Tue, May 25, 2021 at 9:02 AM Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote:
> >
> ......
> >
> > As far as I can tell, this will break if the user wants to use
> > ".mybinary" or ".mydir/mybinary" as the name of their init program.
> >
> > For that matter, it would break "...prog" or "...somedir/prog", which
> > would be strange but not something the kernel should prevent.
> >
>
> Wow, seems I didn't give enough thought to it.
>
> > I don't think this code should be attempting to recreate
> > relative-to-absolute filename resolution.
>
> Trust me, I don't want to do it either. However, I need to check if
> ramdisk_execute_command exist before chroot while the cpio is unpacked
> to '/root'.
>
> Maybe I can check it after chroot, but I need to chroot back if it not
> exist. Can I chroot back in a nice way?
>
> I tried to move the mount on '/root' to '/' before I do this check in
> absolute path, but seems '/' is special, the lookup of '/init' never
> follow the mount on '/' and it can't be found. However, if I lookup
> '/../init', it can be found!
>

I have figured it out. While path lookup, '/' won't follow the mount.
However, with the set of LOOKUP_DOWN, it will be followed.

So I will move the mount on '/root' to '/' and check the exist of
ramdisk_execute_command with LOOKUP_DOWN setted.

Seems there is still a long way to go on kernel......

Thanks!
Menglong Dong