In message <[EMAIL PROTECTED]>, "Paul A. Scott" writes:
>
>-- 
>
>> From: Poul-Henning Kamp <[EMAIL PROTECTED]>
>>>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
[EMAIL PROTECTED]         | 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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