Re: *at syscalls for xattrs?

H. Peter Anvin
2007-07-16T18:02:20Z

Jeff Garzik wrote:
>>
>> What the *at() interfaces really do is fix/paper over a longstanding
>> wart in Unix: the cwd really should have been a standard file descriptor
>> (like stdin/stdout/stderr) instead of a magic piece of state maintained
>> in kernel space.
>
> It's more than a wart, IMO. *at() allows one to close races (with
> potential security implications) that are otherwise impossible to close,
> in directory traversal.
>
> *at() permits a userspace program to hold proper references to all
> objects during a directory traversal, with all that implies.
>

Well, as Jeremy pointed out, in the absence of threads you can do the
same thing with fchdir(), however, that's much more of a hack.

-hpa