Re: Non-root chroot

wouldn't the root access will be contained inside the chroot only?

-------- Original Message --------
On 01/08/25 6:09 pm, Dmitry Mikushin  wrote:

> The fundamental security concern with allowing unprivileged chroot() is privilege escalation through file system manipulation:
>
> - A regular user creates their own directory structure in their home directory (where they have full write permissions)
> - The user creates a fake /etc/passwd file within this structure, containing a password hash for root that they know
> - The user then chroots into this fake filesystem
> - Inside the chroot, when the user runs su (or similar authentication utilities), these programs read what they believe is the system's /etc/passwd file - but it's actually the attacker's crafted version
> - The su command validates the password against the fake password file and grants root privileges
>
> пт, 1 авг. 2025 г. в 14:20, Jason Bacon <bacon4000@gmail.com>:
>
>> I'm wondering if there is any way to perform a simple chroot without
>> having root privileges. The goal is to test software builds with access
>> to a limited set of dependencies, as poudriere does, but outside the
>> FreeBSD ports system, and in some cases on hosts where the user has no
>> root access. This will prevent configure scripts with hard-coded search
>> paths from finding things we don't want them to find. Portability to
>> other POSIX platforms would be desirable as well, but is not essential.
>>
>> It's not clear to me why chroot() wasn't designed to support this use
>> case. There's lots of documentation stating that it's a security risk,
>> but I don't see why it couldn't have been designed to be run by a
>> regular user without escalating privileges inside the chroot. I.e. if
>> user "joe" does such a user-level chroot call, then all chrooted
>> processes run as "joe", but with the path of the chroot dir prepended to
>> every open() call (after $CWD is prepended to relative paths, of
>> course), so that processes can only access files in the chroot dir.
>> User "joe" would have the same privileges inside the chroot that he has
>> on the host. One of the other security concerns mentioned is jail
>> breaks, but if joe managed to escape the chroot, he'd only be hurting
>> himself by borking the test build, so that's not a concern here.
>>
>> It might be possible to port fakechroot
>> (https://github.com/dex4er/fakechroot), proot
>> (https://github.com/proot-me/proot), or something similar, but is there
>> anything else on FreeBSD that can do this?
>>
>> Thanks,
>>
>> Jason
>>
>> --
>> Life is a game. Play hard. Play fair. Have fun.

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