netdev - Re: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 bpf: prevent out of bounds speculation on pointer arithmetic

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Date:   Tue, 12 Mar 2019 10:01:41 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Jann Horn <jannh@...gle.com>, <ast@...nel.org>,
        "zhangyi (F)" <yi.zhang@...wei.com>,
        Zhaohongjiang <zhaohongjiang@...wei.com>,
        <netdev@...r.kernel.org>, <stable@...r.kernel.org>,
        <bpf@...r.kernel.org>
Subject: Re: 979d63d50c0c0f7bc537bf821e056cc9fe5abd38 bpf: prevent out of
 bounds speculation on pointer arithmetic



On 2019/3/12 2:54, Greg KH wrote:
> On Mon, Mar 11, 2019 at 07:13:14PM +0800, Jason Yan wrote:
>>
>>
>> On 2019/3/11 17:41, Daniel Borkmann wrote:
>>> Hi Jason,
>>>
>>> On 03/11/2019 10:18 AM, Jason Yan wrote:
>>>> Hi, Daniel & Greg
>>>>
>>>> This patch (979d63d50c0c bpf: prevent out of bounds speculation on pointer arithmetic) was assigned a CVE (CVE-2019-7308) with a high score:
>>>>
>>>> CVSS v3.0 Severity and Metrics:
>>>> Base Score: 9.8 CRITICAL
>>>>
>>>> And this patch is not in stable-4.4, would you please backport this patch to 4.4?
>>>
>>> We don't handle kernels as old as 4.4, so someone else would need to
>>> do the backporting e.g. from your side. The series has been backported
>>> to the last two most-recent stable kernels at that time (we usually
>>> follow netdev practice here), and there have been asks about 4.14 as
>>> well; I've been looking into backporting for the latter last two weeks
>>> on and off, but there are conflicts all over the place in fragile core
>>> areas where I didn't have enough free cycles to complete it yet. For
>>> old kernels, you're probably better off doing something like this in
>>> your tree instead of the huge complexity with a backport:
>>>
>>
>> Thanks for you kindly reply.
>>
>>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>>> index bc34cf9..2cea2de 100644
>>> --- a/kernel/bpf/syscall.c
>>> +++ b/kernel/bpf/syscall.c
>>> @@ -47,7 +47,7 @@ static DEFINE_SPINLOCK(prog_idr_lock);
>>>    static DEFINE_IDR(map_idr);
>>>    static DEFINE_SPINLOCK(map_idr_lock);
>>>
>>> -int sysctl_unprivileged_bpf_disabled __read_mostly;
>>> +int sysctl_unprivileged_bpf_disabled __read_mostly = 1;
>>>
>>
>> Greg, is it possible to get this kind of mitigation into 4.4?
> 
> Why are you using a 4.4 kernel with untrusted userspace?  The only
> reason to use 4.4.y at this point in time is if you have a huge SoC tree
> patchset that is not upstream.  If you are using x86, you should be
> using 4.14.y or newer right now.
> 
> That being said, no, I am not going to change the default here, that
> could break people's working setups.  I would recommend you just setting
> this value in your initrd/setup scripts if you want it, that's why it is
> a sysctl :)
> 

Got it, thanks.

Jason

> thanks,
> 
> greg k-h
> 
> .
>