Re: [PATCH v1 0/1] Unprivileged chroot

[Casey Schaufler]

On 3/10/2021 8:09 AM, Mickaël Salaün wrote:
> Hi,
>
> The chroot system call is currently limited to be used by processes with
> the CAP_SYS_CHROOT capability.  This protects against malicious
> procesess willing to trick SUID-like binaries.  The following patch
> allows unprivileged users to safely use chroot(2).

Mount namespaces have pretty well obsoleted chroot(). CAP_SYS_CHROOT is
one of the few fine grained capabilities. We're still finding edge cases
(e.g. ptrace) where no_new_privs is imperfect. I doesn't seem that there
is a compelling reason to remove the privilege requirement on chroot().

>
> This patch is a follow-up of a previous one sent by Andy Lutomirski some
> time ago:
> https://lore.kernel.org/lkml/0e2f0f54e19bff53a3739ecfddb4ffa9a6dbde4d.1327858005.git.luto@xxxxxxxxxxxxxx/
>
> This patch can be applied on top of v5.12-rc2 .  I would really
> appreciate constructive reviews.
>
> Regards,
>
> Mickaël Salaün (1):
>   fs: Allow no_new_privs tasks to call chroot(2)
>
>  fs/open.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 61 insertions(+), 3 deletions(-)
>
>
> base-commit: a38fd8748464831584a19438cbb3082b5a2dab15