|| ||Vasiliy Kulikov <segoon-AT-openwall.com> |
|| ||kernel-hardening-AT-lists.openwall.com |
|| ||Re: [kernel-hardening] Re: RLIMIT_NPROC check in set_user() |
|| ||Wed, 6 Jul 2011 22:59:32 +0400|
|| ||linux-kernel-AT-vger.kernel.org, Greg Kroah-Hartman <gregkh-AT-suse.de>,
Andrew Morton <akpm-AT-linux-foundation.org>,
"David S. Miller" <davem-AT-davemloft.net>,
Jiri Slaby <jslaby-AT-suse.cz>, James Morris <jmorris-AT-namei.org>,
Neil Brown <neilb-AT-suse.de>|
|| ||Article, Thread
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()
Honestly, I didn't expect such a positive reaction from you in the first
> 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
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().
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