linux-kernel - Re: bpf: undefined shift in __bpf_prog

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20151204191013.GB45508@ast-mbp.thefacebook.com>
Date:	Fri, 4 Dec 2015 11:10:15 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Alexei Starovoitov <ast@...nel.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
Subject: Re: bpf: undefined shift in __bpf_prog_run

On Fri, Dec 04, 2015 at 08:03:47PM +0100, Dmitry Vyukov wrote:
> > is it with some random seccomp program?
> > If normal libseccomp generates such programs than it needs to be fixed.
> 
> Yes, it is with completely random seccomp program.
> 
> >> Such shifts have undefined behavior according to C standard and behave
> >> differently on different archs. I guess we don't want to rely on any
> >> kind of undefined behavior in bpf/seccomp. And generally want to
> >> completely define results of all operations in bpf.
> >
> > bpf is an engine and we're not going to slow down each shift operation
> > by extra run-time checks or masks.
> > In other words bpf shift instruction == shift in C. Both undefined
> > with for large operands.
> > If seccomp is relying on undefined behavior, it should be fixed.
> 
> But note that it is not that result of such operation is undefined, it
> is overall kernel behavior that becomes undefined.

not true.
just don't generate random bpf programs with such shifts.
kernel is fine.

--
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/