Behavior of exec wrt euid/ruid on 2.2 vs. 2.4 kernels

[Neulinger, Nathan]

I just noticed this today when I upgraded an older machine from 2.2.x to
2.4.18 that the behavior of exec changed with respect to how it handles
euid!=ruid.

Basically, on 2.4:
	setuid bin, execute it, ruid!=euid, exec another tool, now euid
is set to ruid

on 2.2 the execced binary retains the ruid!=euid.

I can see how this might have been done intentionally for security,
however, it does mean that it is impossible for a execced tool to know
the real uid that is running it if executed from a setuid wrapper, or to
run a helper tool (aklog) from a ruid!=euid process. 

Was this change in behavior intentional?

I never noticed it on any of our other 2.4.x systems, cause exec()'s
within setuid bin's without setresuid(geteuid(),geteuid(),geteuid()) are
pretty rare in our tools, most of them just have a single bin that does
whatever it needs to do. 

-- Nathan

------------------------------------------------------------
Nathan Neulinger                       EMail:  [e-mail]
University of Missouri - Rolla         Phone: [phone]
Computing Services                       Fax: [phone]