Date: Wed, 13 Jan 2016 11:33:56 +1100 From: Daniel Axtens <dja@...ens.net> To: Solar Designer <solar@...nwall.com> Cc: Jann Horn <jann@...jh.net>, kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, HATAYAMA Daisuke <d.hatayama@...fujitsu.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, Baoquan He <bhe@...hat.com>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> Subject: Re: [RFC] kernel/panic: place an upper limit on number of oopses Solar Designer <solar@...nwall.com> writes: > Jann Horn <jann@...jh.net> wrote: >> To prevent an attacker from turning a mostly harmless oops into an >> exploitable issue using a refcounter wraparound caused by repeated >> oopsing, limit the number of oopses. > > This may also reduce the likelihood of successful exploitation of some > other vulnerabilities involving memory corruption, where an unsuccessful > attempt may inadvertently trigger an Oops. The attacker would then need > to succeed in fewer than the maximum allowed number of Oops'es. Jann's > currently proposed default of 0x100000 is too high to make a difference > in that respect, but people may set it differently. > > On Wed, Jan 13, 2016 at 10:34:39AM +1100, Daniel Axtens wrote: >> I'm torn between making the limit configurable and not adding to the >> massive proliferation of config options. > > What about reusing panic_on_oops for the configurable limit? The > currently supported values of 0 and 1 would retain their meaning, > 2 would panic after 2nd Oops, and so on. I thought about this, then I looked at where panic_on_oops was used and I thought it would be a pretty invasive change. I'm also nervous about changing the semantics of panic_on_oops under people... > > There's overlap with grsecurity's banning of users on Oops, but I think > it makes sense to have both the trivial change proposed by Jann (perhaps > with the reuse of panic_on_oops for configuration) and grsecurity-style > banning (maybe with a low configurable limit, rather than always on > first Oops). > > Alexander
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