From: Kees Cook <keescook@chromium.org>
To: David Miller <davem@davemloft.net>
Cc: syzbot <syzbot+e2d6cfb305e9f3911dea@syzkaller.appspotmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Network Development <netdev@vger.kernel.org>,
Eric Biggers <ebiggers3@gmail.com>,
James Morse <james.morse@arm.com>,
keun-o.park@darkmatter.ae, Laura Abbott <labbott@redhat.com>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH] net: Whitelist the skbuff_head_cache "cb" field
Date: Fri, 9 Feb 2018 08:01:12 +1100 [thread overview]
Message-ID: <CAGXu5jJsmECUtyXBJb60o_Ve3PTUw8pkyaH2=SFHSxHy1vjsmA@mail.gmail.com> (raw)
In-Reply-To: <20180208.151621.581060088482890871.davem@davemloft.net>
On Fri, Feb 9, 2018 at 7:16 AM, David Miller <davem@davemloft.net> wrote:
> From: Kees Cook <keescook@chromium.org>
> Date: Wed, 7 Feb 2018 17:44:38 -0800
>
>> Most callers of put_cmsg() use a "sizeof(foo)" for the length argument.
>> Within put_cmsg(), a copy_to_user() call is made with a dynamic size, as a
>> result of the cmsg header calculations. This means that hardened usercopy
>> will examine the copy, even though it was technically a fixed size and
>> should be implicitly whitelisted. All the put_cmsg() calls being built
>> from values in skbuff_head_cache are coming out of the protocol-defined
>> "cb" field, so whitelist this field entirely instead of creating per-use
>> bounce buffers, for which there are concerns about performance.
>>
>> Original report was:
> ...
>> Reported-by: syzbot+e2d6cfb305e9f3911dea@syzkaller.appspotmail.com
>> Fixes: 6d07d1cd300f ("usercopy: Restrict non-usercopy caches to size 0")
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> ---
>> I tried the inlining, it was awful. Splitting put_cmsg() was awful. So,
>> instead, whitelist the "cb" field as the least bad option if bounce
>> buffers are unacceptable. Dave, do you want to take this through net, or
>> should I take it through the usercopy tree?
>
> Thanks Kees, I'll take this through my 'net' tree.
Cool, thanks. And just to be clear, if it's not already obvious, this
patch needs kmem_cache_create_usercopy() which just landed in Linus's
tree last week, in case you've not merged yet.
-Kees
--
Kees Cook
Pixel Security
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next prev parent reply other threads:[~2018-02-08 21:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-08 1:44 Kees Cook
2018-02-08 20:16 ` David Miller
2018-02-08 21:01 ` Kees Cook [this message]
2018-02-08 21:04 ` David Miller
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