Date: Thu, 16 Sep 2010 14:51:54 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Oleg Nesterov <oleg@...hat.com> Cc: kosaki.motohiro@...fujitsu.com, Roland McGrath <roland@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, oss-security@...ts.openwall.com, Solar Designer <solar@...nwall.com>, Kees Cook <kees.cook@...onical.com>, Al Viro <viro@...iv.linux.org.uk>, Neil Horman <nhorman@...driver.com>, linux-fsdevel@...r.kernel.org, pageexec@...email.hu, "Brad Spengler <spender@...ecurity.net>, Eugene Teo" <eugene@...hat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Subject: Re: [PATCH] move cred_guard_mutex from task_struct to signal_struct > On 09/10, KOSAKI Motohiro wrote: > > > > 1) moving cread_guard_mutex itself > > - no increase execve overhead > > -> very good > > - it also prevent parallel ptrace > > No, it doesn't. Only PTRACE_ATTACH needs this mutex, and as Roland > pointed out it also needs write_lock(tasklist) which is worse. So > this change doesn't make any practical harm for ptrace. I see, thanks. > > > 2) move in_exec_mm to signal_struct too > > -> very hard. oom-killer can use very few lock because it's called > > from various place. now both ->mm and ->in_exec_mm are protected > > task_lock() and it help to avoid messy. > > Yes. But, if ->in_exec_mm is only used by oom_badness(), then I think > you can use task_lock(tsk->group_leader). oom_badness() needs tasklist > anyway, this means it can't race with de_thread() changing the leader. > But up to you. Good idea. will fix. > > Another very minor nit (but again, up to you). Perhaps exec_mmap() > could clear ->in_exec_mm (in task_struct or signal_struct, this doesnt > matter), it takes task_lock(current) anyway (and at this point current > is always the group leader). Thanks. will fix. > > > Let's move ->cred_guard_mutex from task_struct to signal_struct. It > > naturally prevent multiple-threads-inside-exec. > > Reviewed-by: Oleg Nesterov <oleg@...hat.com> > > > This is very minor, but perhaps you can also fix a couple of comments > which mention task->cred_guard_mutex, > > fs/exec.c:1109 the caller must hold current->cred_guard_mutex > kernel/cred.c:328 The caller must hold current->cred_guard_mutex > include/linux/tracehook.h:153 @task->cred_guard_mutex Will fix, of cource.
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