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: <20151204203522.GB64517@ast-mbp.thefacebook.com>
Date:	Fri, 4 Dec 2015 12:35:23 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	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 08:48:57PM +0100, Dmitry Vyukov wrote:
> 
> For example, a compiler can assume that result of left shift is larger
> or equal to first operand, which in turn can allow it to elide some
> bounds check in code, which in turn can lead to an exploit. I am not
> saying that this particular pattern is present in the code, what I
> want to say is that such undefined behaviors can lead to very
> unpredictable and unexpected consequences.

Within bpf it cannot.
shift is not used in any memory or bounds operations.
so reg <<= 1234 cannot be exploited.

--
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/