Re: Setreuid distinction about (uid_t)-1

From: Adrián
Date: Tue Jul 17 2012 - 12:57:01 EST

On Tue, Jul 17, 2012 at 5:24 PM, Theodore Ts'o <tytso@xxxxxxx> wrote:
> On Tue, Jul 17, 2012 at 03:13:18PM +0100, Adrián wrote:
>> Thanks a lot Athanasius. What I still can't see is why is the -1
>> exception there, as I assume that if you want to leave one of the ids
>> unchaged you can call:
>> setreuid(0,geteuid());
>> If you want to leave euid unchanged, right? Is there a need or reason
>> to be doing this differentiation in the setreuid code?
> Unix systems for multiple decades have done things this way, and it's
> ensrined in POSIX and the Single Unix Specification. Changing it
> would potentially open up security holes for programs which expect the
> standard-specificed behavior.
> (Note, BTW, that decades ago system calls weren't cheap, and CPU's
> were much slower, and that may have driven the historical behavior.
> Sometimes we get forget how spoiled we are that Linux's system call
> overhead is as low as it is...)
> - Ted
Thanks for that Theo!
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