Messages in this thread | | | Date | Thu, 7 Jul 2011 12:19:30 +0400 | From | Vasiliy Kulikov <> | Subject | Re: [kernel-hardening] Re: RLIMIT_NPROC check in set_user() |
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(Sorry, I've dropped Linus from CC somehow ;-)
On Wed, Jul 06, 2011 at 22:59 +0400, Vasiliy Kulikov wrote: > 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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