Date: Tue, 24 Dec 2002 15:15:54 +0100 From: phk@freebsd.org To: "Paul A. Scott" <pscott@skycoast.us> Cc: current@freebsd.org Subject: Re: revoke(2) redux... Message-ID: <1412.1040739354@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 24 Dec 2002 06:09:30 PST." <BA2DAA9A.17D62%pscott@skycoast.us>
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In message <BA2DAA9A.17D62%pscott@skycoast.us>, "Paul A. Scott" writes:
>
>--
>
>> From: Poul-Henning Kamp <phk@FreeBSD.ORG>
>>>void setctty(char *name) {
>>> (void) revoke(name);
>>> if ((fd = open(name, O_RDWR)) == -1) {
>> Isn't there a pretty obvious race between the revoke() and the open() ?
>> Wouldn't it in fact make much more sense if revoke(2) was defined as
>> int revoke(int fd); /* kick everybody else off */
>> and the code above would look like:
>>> if ((fd = open(name, O_RDWR)) == -1) {
>>> }
>>> (void) revoke(fd);
>
>But, revoke() invalidates all descriptors for the named path, so any
>subsequent operations on the open file descriptor would fail, which defeats
>the purpose of open().
I think you missed the fine point in the "kick everybody *else*
off" comment.
>I think what's needed is some form of serialization
>around revoke() and open(). I'm not a master of the init code, but it may be
>that the code is inherently non-reentrant, so the original code would then
>be okay.
There is more code like this in places. The point is you cannot serialize
against other processes.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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