access(2) (was: Writing to A NON-Existing File in "C")

[Michael I. Bushnell]

In article <887 at cresswell.quintus.UUCP> ok at quintus.UUCP (Richard A. O'Keefe) writes:
>In article <14020030 at hpisod2.HP.COM>, decot at hpisod2.HP.COM (Dave Decot) writes:
>> access(2) should not be used to determine the other access permissions
>> except in setuid programs, and even then, not for testing execute
>> access by setuid-root programs.
>
>If a program which is never intended to run setuid ensures that it is
>not being run setuid or setgid by doing

[Code fragment to test for suid conditions]

>where is the harm in subsequently using access(2) to test for permission to
>read or write a file?
>
>Is there any legitimate reason why someone might take a program which was
>not originally designed to run setuid or setguid and do chmod u+s
>or chmod g+s to it?


Not really.  But there is another way it can run under suid
conditions:

% whoami
foo
% su
Password:
# nifty_program


Note that nifty program will now have REAL uid foo and EFFECTIVE uid
root.


                N u m q u a m   G l o r i a   D e o 

			Michael I. Bushnell
			HASA - "A" division
14308 Skyline Rd NE				Computer Science Dept.
Albuquerque, NM  87123		OR		Farris Engineering Ctr.
	OR					University of New Mexico
mike at turing.unm.edu				Albuquerque, NM  87131
{ucbvax,gatech}!unmvax!turing.unm.edu!mike