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SubjectRe: real POSIX.1b semaphores

"Theodore Y. Ts'o" <tytso@MIT.EDU> writes:

> Err.... be careful about the security issues. It should not be possible
> for a process which doesn't have access to a semaphore to just go into
> the shared page and much with the sempahores. This pretty much tosses
> out any idea where you use a single global page for all sempahores.....

Unfortunately there are not many security consideration in the POSIX
semaphores. Either they are process local or they are available
for any process. I read the section about semaphores twice and
found no sign for protection.

Gallmeister's book speaks about protection for named semaphores (and
it sounds reasonable). Nothing is specified for memory semaphores.
This really seems to be a whole in the standard.

Oh well. But since it is not specified otherwise we might allow
every process to read the value of a semaphore. Since the changing
(wait or post) happens in the kernel the later can perform the
needed verification.

-- Uli
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Ulrich Drepper \ ,--------------------' \ 76149 Karlsruhe/Germany
Cygnus Support `--' `------------------------

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