On Wed, 2005-03-30 at 19:40 +0200, Jacek Łuczak wrote: > Hi > > I made some tests and almost all Linux distros brings down while freebsd > survive!Forkbombing is a big problem but i don't think that something like > > max_threads = mempages / (16 * THREAD_SIZE / PAGE_SIZE); > > is good solution!!! > How about add max_user_threads to the kernel? It could be tunable via > proc filesystem. Limit is set only for users. > I made a fast:) patch - see below - and test it on 2.6.11, > 2.6.11ac4,2.6.12rc1...works great!!!New forks are stoped in > copy_process() before dup_task_struct() and EAGAIN is returned. System > works without any problems and root can killall -9 forkbomb. >
I really liked this approach because: * it is similar to other *nixes. (freebsd, openbsd) * it is easily tuneable (/proc or systcl) * it is stupid simple - small chance that things can go wrong. * this solves *many* things in comparation to possible problems it causes. Only thing that could be a problem that I come to think of is that you cannot raise the limit through /etc/security/limits.conf or similar. Eg. you migh want all setuid() services/daemons run with a low limit but you want give user Bob more processes. (I don't know if this is a realistic situation though) The default value could be something like: max_user_threads = max_threads / 2 or: max_user_threads = max_threads / 4; With a lower limit to 20 or something, just like max_threads (in case you try run Linux on 2MiB RAM) If a fixed value (like 300, 512, 2000) is used then will probably systems with low amount of RAM be vulerable to the forkbomb attack. -- Natanael Copa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
