Messages in this thread | | | Date | Wed, 6 Jul 2011 22:59:32 +0400 | From | Vasiliy Kulikov <> | Subject | Re: [kernel-hardening] Re: RLIMIT_NPROC check in set_user() |
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On Wed, Jul 06, 2011 at 11:01 -0700, Linus Torvalds wrote: > My reaction is: "let's just remote the crazy check from set_user() > entirely".
Honestly, I didn't expect such a positive reaction from you in the first reply :)
> The whole point of RLIMIT_NPROC is to avoid fork-bombs.
It is also used in cases where there is implicit or explicit limit on some other resource per process leading to the global limit of RLIMIT_NPROC*X. The most obvious case of X is RLIMIT_AS.
Purely pragmatic approach is introducing the check in execve() to heuristically limit the number of user processes. If the program uses PAM to register a user session, maxlogins from pam_limits is the Right Way. But many programs simply don't use PAM because of the performance issues. E.g. apache doesn't use PAM. On a shared web hosting this is a real issue.
In -ow patch execve() checked for the exceeded RLIMIT_NPROC, which effectively solved Apache's problem.
...and execve() error handling is hard to miss ;-)
> So let's keep it in kernel/fork.c where we actually create a *new* > process (and where everybody knows exactly what the limit means, and > people who don't check for error cases are just broken). And remove it > from everywhere else.
There are checks only in copy_process() and set_user().
Thanks,
-- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments
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