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Aunc.1056 fa.unix-wizards utzoo!decvax!duke!unc!smb Thu Aug 20 18:15:47 1981 setuid programs, locking I've attempted to send this item to fa.unix-wizards via the ARPAnet; in case it doesn't make it, here it is again for all you Usenet fans.

Much more use should be made of the FIOCLEX ioctl call. Setuid programs that don't use it run the risk of some child process they spawn -- say, in response to ! requests -- finding interesting files open. And this would answer a question raised about the lock driver -- what should happen when the process that opened it terminates. If it had used FIOCLEX on the lock file, there would be no problem about the "feature" of UNIX that was mentioned. By the way, I would suggest that the error code in that driver be changed to return EBUSY rather than EPERM; that way, some lock special files could be restricted to certain users, programs, etc -- you might not want a random user grabbing the lock on /etc/passwd, say.

A few other comments on the lock driver: (a) it doesn't allow for locking of arbitrary objects, such as uucp's ttys, or individual mailboxes; (b) it doesn't allow "read-only" access to a locked object. That is, I may want to lock a database record to examine it. Anyone else should be allowed to examine it, but no one should be allowed to modify it till I release the lock. (c) it would be nice to be able to sleep in the kernel on a lock request; if you want to time out, you can use alarm() yourself; (d) does anyone know anything about the ONYX locking code? I understand that they have placed it in the public domain (at least to holders of WE licenses) so that it could become "standard".

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