- Source: 'man beep'
- IOCTL WACKINESS
- Some users will encounter a situation where beep dies with a complaint from ioctl(). The reason for this, as Peter Tirsek was nice
- enough to point out to me, stems from how the kernel handles beep's attempt to poke at (for non-programmers: ioctl is a sort of
- catch-all function that lets you poke at things that have no other predefined poking-at mechanism) the tty, which is how it beeps.
- The short story is, the kernel checks that either:
- - you are the superuser
- - you own the current tty
- What this means is that root can always make beep work (to the best of my knowledge!), and that any local user can make beep work,
- BUT a non-root remote user cannot use beep in it's natural state. What's worse, an xterm, or other x-session counts, as far as the
- kernel is concerned, as 'remote', so beep won't work from a non-privileged xterm either. I had originally chalked this up to a bug,
- but there's actually nothing I can do about it, and it really is a Good Thing that the kernel does things this way. There is also a
- By default beep is not installed with the suid bit set, because that would just be zany. On the other hand, if you do make it suid
- root, all your problems with beep bailing on ioctl calls will magically vanish, which is pleasant, and the only reason not to is that
- any suid program is a potential security hole. Conveniently, beep is very short, so auditing it is pretty straightforward.
- Decide for yourself, of course, but it looks safe to me - there's only one buffer and fgets doesn't let it overflow, there's only one
- file opening, and while there is a potential race condition there, it's with /dev/console. If someone can exploit this race by
- replacing /dev/console, you've got bigger problems. :)
- So the quick, only, and likely safe solution if beep is not beeping when you want it to is (as root):
- # chmod 4755 /usr/bin/beep
- (or wherever you put it)
- The one snag is that this will give any little nitwit the ability to run beep successfully - make sure this is what you want. If it
- isn't, a slightly more complex fix would be something like:
- # chgrp beep /usr/bin/beep
- # chmod 4750 /usr/bin/beep
- and then add only beep-worthy users to the 'beep' group.
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