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Message-ID: <20220604202219.GA25285@openwall.com>
Date: Sat, 4 Jun 2022 22:22:19 +0200
From: Solar Designer <solar@...nwall.com>
To: tr3e wang <tr3e.wang@...il.com>
Cc: oss-security@...ts.openwall.com
Subject: Re: CVE-2021-4204: Linux Kernel eBPF Improper Input Validation Vulnerability
Hi,
I've attached the exploit from the linux-distros thread - hopefully, the
right one. (I really shouldn't be the one doing it. The exploit author
is most qualified to do it, as required by linux-distros list policy.)
Alexander
On Wed, Jun 01, 2022 at 02:55:13PM +0200, Solar Designer wrote:
> Hi,
>
> In context of the recent discussions on linux-distros list policies and
> their enforcement, I looked at some of the previously handled issues,
> and identified that the below wasn't properly handled/enforced.
>
> tr3e, since you had shared actual exploit code with linux-distros, you
> were supposed to post the _code_ to oss-security within 7 days after
> your initial public disclosure of the vulnerability. However, you only
> posted "the exploit overview" and promised that "Full exploit code will
> be published on github in the near future." Apparently, the latter
> never happened, and it wouldn't have satisfied the requirement anyway.
>
> Please post the same exploit code you had shared with linux-distros to
> this thread on oss-security ASAP. Thank you!
>
> Alexander
>
> On Tue, Jan 18, 2022 at 09:26:43PM +0800, tr3e wang wrote:
> > Hi all,
> >
> > This post is the exploit overview of CVE-2021-4202.
> >
> > We successfully exploited this vulnerability to obtain full root
> > privileges on default installations of Ubuntu 20.04.
> >
> > *Exploit overview*
> >
> > 1. We create a lot of BPF ringbufs, and choose one of them as victim.
> > The BPF_FUNC_ringbuf_reserve allow us to have a pointer A to the
> > beginning of the victim ringbuf's data field.
> >
> > 2. We do a pointer subtraction to point back to the victim ringbuf's
> > mask field and overwrite it to 0x80000fff through
> > BPF_FUNC_ringbuf_submit.
> > This allows us to do a limited out-of-bounds read/write. If lucky,
> > we can read/write all the fields of the ringbuf behind the victim.
> >
> > 3. With the full control over all fields of the ringbuf behind the
> > victim, we can manipulate the ringbuf to achieve a restricted
> > address read/write with side effects in the vmalloc space.
> >
> > 4. We spawn many child processes, and use restricted address read to
> > find the address of task_struct and cred in the vmalloc space.
> > After zeroing out the uid/gid/... , full root privileges obtained.
> >
> > Full exploit code will be published on github in the near future.
> >
> > Regards,
> > tr3e
Download attachment "full-exploit.tar.gz" of type "application/x-gzip" (14094 bytes)
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