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Date: Tue, 18 Jan 2022 21:29:18 +0800
From: tr3e wang <tr3e.wang@...il.com>
To: oss-security@...ts.openwall.com
Subject: Re: Linux Kernel eBPF Improper Input Validation Vulnerability
Hi all,
This post is the exploit overview of CVE-2022-23222.
We successfully exploited this vulnerability to obtain full root
privileges on default installations of Ubuntu 20.04.
*Exploit overview*
1. Among all these *_OR_NULL types, we choose PTR_TO_MEM_OR_NULL
which can be created by BPF_FUNC_ringbuf_reserve. First, we
pass 0xffff........ffff to BPF_FUNC_ringbuf_reserve to get a
NULL pointer r0, and copy r0 to r1. Then add r1 by 1, and do
NULL check on r0. At this point, the verifier will believe that
both r0 and r1 are zero.
2. ALU sanitation is hardened after commit
"bpf: Fix leakage of uninitialized bpf stack under speculation".
To bypass alu sanitation, we use helper func bpf_skb_load_bytes_*
to get partial/full overwrite the pointer on stack to obtain
pointer address leakage and arbitrary address read/write.
3. We spawn many child processes, and use arbitrary address read to
find the address of task_struct and cred around the the address of
the array map we created. After zeroing out the uid/gid/... ,
full root privileges obtained.
Full exploit code will be published on github in the near future.
Regards,
tr3e
tr3e wang <tr3e.wang@...il.com> 于2022年1月13日周四 16:21写道：
> Hi all,
>
> This vulnerability allows local attackers to escalate privileges on
> affected installations of Linux Kernel. An attacker must first obtain the
> ability to execute low-privileged code on the target system in order to
> exploit this vulnerability.
>
> The specific flaw exists within the handling of eBPF programs. The issue
> results from the lack of proper validation of user-supplied eBPF programs
> prior to executing them. An attacker can leverage this vulnerability to
> escalate privileges and execute code in the context of the kernel.
> BE AWARE, unprivileged bpf is disabled by default in most distros.
>
> *Affected Version*
>
> Linux Kernel 5.8 or later
>
> *Root Cause Analysis*
>
> The bpf verifier(kernel/bpf/verifier.c) did not properly restrict several
> *_OR_NULL pointer types which allows these types to do pointer arithmetic.
> This can be leveraged to bypass the verifier check and escalate privilege.
> (see
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/bpf/verifier.c?h=v5.10.83#n6022
> )
>
> *Exploit Code*
>
> Exploit code will be delayed for 5 days and will be posted at 12:00 UTC,
> Jan 18, 2022
>
> *Mitigations*
>
> set kernel.unprivileged_bpf_disabled to 1
>
> BE AWARE AGAIN, unprivileged bpf is disabled by default in most distros.
>
> *Credits*
>
> tr3e of SecCoder Security Lab
> Best,
> tr3e
>
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