On Wed, Jul 11, 2018 at 08:22:41AM +0100, David Howells wrote:
> Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>
> > > sfd = fsopen("ext4", FSOPEN_CLOEXEC);
> > > write(sfd, "s /dev/sdb1"); // note I'm ignoring write's length arg
> >
> > Imagine some malicious program passes sfd as stdout to a setuid
> > program. That program gets persuaded to write "s /etc/shadow". What
> > happens? You’re okay as long as *every single fs* gets it right, but that’s
> > asking a lot.
>
> Do note that you must already have CAP_SYS_ADMIN to be able to call fsopen().
>
> David
Not really, by default an unprivileged user can still do:
unshare(CLONE_NEWUSER|CLONE_NEWNS);
syscall(__NR_fsopen, "ext4", 0);
- Eric
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