[PATCH] libbb: Only setgid/setuid when necessary

[Steven McDonald]

On Mon, 10 Jul 2017 09:17:09 +0200
Denys Vlasenko <vda.linux at googlemail.com> wrote:

> * Don't check for errors: in normal use, they are impossible

I don't think this is correct. From setuid(2):

> EAGAIN
>    The uid does not match the current uid and uid brings process over
>    its RLIMIT_NPROC resource limit.

This would enable a trivial privilege elevation to root attack on a
system with setuid busybox. All the user needs to do is fork a lot of
processes up to RLIMIT_NPROC, and then have one of them exec busybox's
ash.