Usefulness of access(2) - (nf)

[Mark Brukhartz]

In response to spanky!ka, regarding a proposed replacement for access(2):

	I see little need for a function to check for access permission on a
	file by the effective user/group id.  Simply doing a stat(2) on the
	file will achieve the same result.

An eaccess(2) has been proposed to check access by effective user- and group-
ids. Rather than adding another single-purpose system call, I'd rather replace
access(2) with a more general case. There would, of course, be a compatibility
function in libc. Note that stat(2) doesn't check parent directory permissions.

	The problems with the proposed pathaccess system call are twofold.
	First, it would require a lot more work to implement than access.
	Access simply resets the effective id's temporarily and calls nami
	to check the permissions; the proposed new call would have to do its
	own path search.

I didn't say that it would be easy [:-)].

	The second problem has to do with security. Access will perform a
	directory search even if the effective user id doesn't have execute
	permission on a directory. In the case of the more general call, care
	would have to be taken to ensure that such searches didn't create a
	security hole.

Now things become messier. Directory access would have to be restricted by
the effective user- and group-ids of the invoker. This would break access()
when a component directory can by "executed" by the real user- and group-ids,
but not the effective ones. Perhaps this would all be easier with stacked
user- and group-ids, but that "improvement" has been argued already. Oh, well...

				Mark Brukhartz
				..!{allegra,ihnp4,ittral,trsvax}!laidbak!mark