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Message-ID: <7c124869-2387-dac5-2a26-deda05e18ede@virtuozzo.com>
Date: Fri, 25 May 2018 15:04:15 +0300
From: Evgenii Shatokhin <eshatokhin@...tuozzo.com>
To: oss-security@...ts.openwall.com, Andrey Konovalov <andreyknvl@...il.com>
Cc: Vladis Dronov <vdronov@...hat.com>
Subject: Re: CVE-2018-1130: Linux kernel: dccp: a null pointer
dereference in net/dccp/output.c:dccp_write_xmit
On 25.05.2018 13:48, Andrey Konovalov wrote:
> On Wed, May 23, 2018 at 4:57 PM, Kurt Seifried <kseifried@...hat.com> wrote:
>> On Wed, May 23, 2018 at 8:49 AM, Andrey Konovalov <andreyknvl@...il.com>
>> wrote:
>>
>>> On Thu, May 10, 2018 at 2:05 PM, Vladis Dronov <vdronov@...hat.com> wrote:
>>>> Hello,
>>>>
>>>> A null pointer dereference in dccp_write_xmit() function in
>>> net/dccp/output.c
>>>> in the Linux kernel before v4.16-rc7 allows a local user to cause a
>>> denial of
>>>> service by a number of certain crafted system calls.
>>>
>>
>>
>> So the classic CVE statement for this is "does it cross/violate a trust
>> boundary". Yeah I know, not super helpful.
>>
>> In general when I look at something and need to decide whether or not it
>> deserves/needs a CVE the fundamentals are:
>>
>> 1) Can an attacker use this vulnerability to gain access, additional
>> privileges, basically is there an impact to
>> Confidentiality/Availability/Integrity? This is really two tests: is there
>> an impact, and is there a way for the attacker to trigger or exploit it?
>> That's a CVE.
>>
>> 2) Does the software/system make a specific security claim that they then
>> fail to meet? E.g. "we include a firewall that blocks access to everything
>> inbound except for port 22", if they were to then also allow port 80,
>> that'd be a CVE.
>>
>> So for the syzbot stuff mostly what you need to determine is:
>>
>> a) is there a security related impact?
>> AND
>> b) can an attacker trigger it?
>>
>> If both are yes, then a CVE is warranted.
>
> Hi Kurt,
>
> Perhaps I should've been more clear. I wasn't asking "what qualifies
> for a CVE?", but rather "There are a 100 bugs that qualify for CVEs,
> how do single out 10 of them to actually request CVEs for?".
>
> In particular, the 100 bugs that I'm referring to are the bugs
> reported by syzbot (perhaps there's even more:
> https://syzkaller.appspot.com/?fixed=upstream) and the 10 bugs (or so)
> are the ones Vladis announced on oss-security over the last few
> months. I'm just curious how did he choose those 10 bugs out of that
> 100+.
If I understand it correctly, Syzkaller programs run as root. Therefore,
it is still needed to check which of the bugs it has found are security
flaws.
As for this particular bug in dccp_write_xmit() - I stumbled upon that
Syzbot's report and checked that the bug was exploitable by an
unprivileged user if dccp modules were loaded. Then I reported the
problem to RedHat, and they desided to request a CVE for that. The
problem is not critical for RHEL, by the way, but still.
I don't know, if the process was the same for other bugs found by
Syzkaller they requested CVEs for.
Regards,
Evgenii
>
> Thanks!
> .
>
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