Re: [PATCH] Add supplementary UIDs, and getusers/setusers system calls

[Andy Lutomirski]

On Nov 20, 2014 7:16 AM, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> wrote:
>
> Josh Triplett <josh@xxxxxxxxxxxxxxxx> writes:
>
> > Analogous to the supplementary GID list, the supplementary UID list
> > provides a set of additional user credentials that a process can act as.
> > A process with CAP_SETUID can set its UID list arbitrarily; a process
> > without CAP_SETUID can only reduce its UID list.
> >
> > This allows each user to have a set of UIDs that they can then use to
> > further sandbox individual child processes without first escalating to
> > root to change UIDs.  For instance, a PAM module could give each user a
> > block of UIDs to work with.
>
> A couple of quick comments on this patch.
>
> 1) user namespaces already allow you to do this.

I thought you could only map your fsuid. Can you set fsuid to a
supplementary group?

>
> 2) After having looked at the group case I am afraid this intersects in
>    an unfortunate way with user namespaces.
>
> 3) This intersects in a very unfortunate way with setresuid.
>    Applications that today know they are dropping all privileges
>    won't be dropping all privielges with this change.  Which sounds like
>    a recipe for a security exploit to me.
>
> Eric
> --
> To unsubscribe from this list: send the line "unsubscribe linux-api" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/