Re: [PATCH] Add supplementary UIDs, and getusers/setusers system calls
From: Andy Lutomirski
Date: Thu Nov 20 2014 - 13:18:35 EST
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
> 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.
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