linux-kernel - Re: Setreuid distinction about (uid

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Message-ID: <CAFDTedoBOijJdw4zAEYgHzJL8GEoe32Uxy5Em-qaxqFFx0L2UQ@mail.gmail.com>
Date:	Tue, 17 Jul 2012 17:56:42 +0100
From:	Adrián <adrianbn@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>,
	Adrián <adrianbn@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Setreuid distinction about (uid_t)-1

On Tue, Jul 17, 2012 at 5:24 PM, Theodore Ts'o <tytso@....edu> 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!
Adrian
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