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Date: Wed, 15 Feb 2012 16:38:16 +0100 From: Oleg Nesterov <oleg@...hat.com> To: Cyrill Gorcunov <gorcunov@...nvz.org> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Pavel Emelyanov <xemul@...allels.com>, Andrey Vagin <avagin@...nvz.org>, KOSAKI Motohiro <kosaki.motohiro@...il.com>, Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, Glauber Costa <glommer@...allels.com>, Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>, Matt Helsley <matthltc@...ibm.com>, Pekka Enberg <penberg@...nel.org>, Eric Dumazet <eric.dumazet@...il.com>, Vasiliy Kulikov <segoon@...nwall.com>, Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu, Michal Marek <mmarek@...e.cz>, Frederic Weisbecker <fweisbec@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org Subject: Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree On 02/15, Cyrill Gorcunov wrote: > > On Wed, Feb 15, 2012 at 03:36:06PM +0100, Oleg Nesterov wrote: > > > > > + > > > + /* > > > + * One should have enough rights to inspect task details. > > > + */ > > > + if (!ptrace_may_access(task1, PTRACE_MODE_READ) || > > > + !ptrace_may_access(task2, PTRACE_MODE_READ)) { > > > + ret = -EACCES; > > > > Well, probably this is fine... but may be you can add a comment. > > The task can change its credentials right after ptrace_may_access() > > succeeds. This _looks_ wrong, perhaps it makes sense to add the > > "we do not care" note. > > > > Wait, how it's differ from other ptrace_may_access calls all over > the kernel? I suppose I'm missing something obvious? For example? Say, mm_access() is fine because it returns ->mm which we are going to play with. But map_files_d_revalidate/proc_map_files_get_link looks wrong, there are obviously racy and should use mm_access(). Probably something else is wrong too. Once again, I am not saying that this code really has the security problems. I simply do not know. But it looks wrong without the comment. I do not really understand why do we need ptrace_may_access(), but whatever reason we have how we can trust it? Say, when KCMP_VM checks ->mm, all we know is that PTRACE_MODE_READ succeed in the past. This looks confusing, imho. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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