Re: [PATCH] private mounts

[Miklos Szeredi <miklos@szeredi.hu>]

> Not necessary.
> 
> Why not have the FUSE daemon keep open a file descriptor for the
> directory it's mounted on, and have it sent that to new would-be
> mounters of the same directory using a unix domain socket (rather as
> Pavel suggested)?

How does that help?  It doesn't matter _which_ process you try to bind
mount /proc/XXX/fd/N from, the result will be the same.

> No.  The check is to prevent processes in chroot jails from accessing
> directories outside their jail.  Even CAP_SYS_ADMIN processes must be
> forbidden from doing that.

As someone pointed out, CAP_SYS_ADMIN processes can already escape the
chroot jail with CLONE_NEWNS.  (fd=open("."); clone(CLONE_NEWNS);
[child:] fchdir(fd); chdir(".."))

> But proc_check_root is unnecessarily strict, in that it prevents a
> process from traversing into a "child" namespace.
> 
> IMHO, a better security restriction anyway would be for processes in
> chroot jails to not be able to see processes outside the jail in /proc
> - only processes inside the jail should be visible.  I think everyone
> agrees that would be best.

Dunno.  It's a big change possibly breaking existing applications.
Chroot probably has other uses than jailing.

> If that were implemented, then proc_check_root would be redundant and
> could be removed entirely.

Yes. 

Miklos
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