Discussion:
fwd: [vs-plain] Kernel heap overflow in bpf leading to LPE (exploit provided)
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Yves-Alexis Perez
2018-11-23 17:22:09 UTC
Permalink
Hi list,

we were notified on the Linux distros list of a vulnerability in the bpf
subsystem of the Linux kernel.

I asked the reported (Wei Wu) if ***@k.o had been notified, and
this was done in the following mail, leading Eric Dumazet to suggest
posting this on netdev.

In turn, this has been done just afterwards [1] so the issue is now
public. According to the linux-distros list policy, the original
reporter should also have made the issue public here, but failed to do
that.

I'm posting this right now in order to raise awareness for the
distributions already including 4.19 in a supported release.

As the original mail indicates, an exploit code had been provided by the
reporter, but I intend to wait until a 4.19 kernel including the patch
is released (but not after next Thursday) to publish it as a followup.

Regards,
--
Yves-Alexis

[1] https://marc.info/?l=linux-netdev&m=154290236228315&w=2

----- Forwarded message from Wei Wu <***@gmail.com> -----

Date: Thu, 22 Nov 2018 21:45:11 +0800
From: Wei Wu <***@gmail.com>
To: linux-***@vs.openwall.org
Subject: [vs-plain] Kernel heap overflow in bpf leading to LPE (exploit provided)
X-Mailer: MIME-tools 5.501 (Entity 5.501)
Message-ID: <CACmwppyMMd+T87DytX=X_KzmK+b3Dpx8zBp5GXrPaywKAzN-***@mail.gmail.com>

Hello,

I am writing to report a heap overflow vulnerability in kernel bpf module
There is an integer-overflow-to-buffer-overflow vulnerability in the
bpf functions introduced in 4.19 and affect up to 4.20-rc3, attached
is an LPE exploit which is able to spawn a root shell.
I will first introduce the root cause vulnerability and then discuss
how to fix this vulnerability.

In the following code shows a integer overflow when calculating size =
attr->max_entries + 1;
size is used to calculate queue_size in line 72, and queue size is
used to malloc,
if attr->max_entries is 0xffffffff, then size will be zero, which
result in a smaller buffer allocated.

static struct bpf_map *queue_stack_map_alloc(union bpf_attr *attr)
63 {
64 int ret, numa_node = bpf_map_attr_numa_node(attr);
65 struct bpf_queue_stack *qs;
66 u32 size, value_size;
67 u64 queue_size, cost;
68
69 size = attr->max_entries + 1;
70 value_size = attr->value_size;
71
72 queue_size = sizeof(*qs) + (u64) value_size * size;
73
74 cost = queue_size;
75 if (cost >= U32_MAX - PAGE_SIZE)
76 return ERR_PTR(-E2BIG);
77
78 cost = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
79
80 ret = bpf_map_precharge_memlock(cost);
81 if (ret < 0)
82 return ERR_PTR(ret);
83
84 qs = bpf_map_area_alloc(queue_size, numa_node);



later in function queue_stack_map_push_elem we can overflow this
buffer with arbitrary length with user-controllable content.

229 dst = &qs->elements[qs->head * qs->map.value_size];
230 memcpy(dst, value, qs->map.value_size);


running the exploit gives me a root shell in a custom compiled 4.20-rc3 system:

***@test:~$ ./exp
rop_payload_initialized
uid=0(root) gid=0(root) groups=0(root) context=system_u:system_r:kernel_t:s0
# uname -a
Linux syzkaller 4.20.0-rc3 #1 SMP Thu Nov 22 15:12:38 CST 2018 x86_64 GNU/Linux
#


To fix this vulnerability, we should add check prevent the integer overflow.

Luckily it does not affect any distributions now, hope it get fixed soon : )

--
Wei Wu (ww9210)
University of Chinese Academy of Sciences


----- End forwarded message -----
--
Yves-Alexis Perez
Greg KH
2018-11-23 18:09:14 UTC
Permalink
Post by Yves-Alexis Perez
Hi list,
we were notified on the Linux distros list of a vulnerability in the bpf
subsystem of the Linux kernel.
this was done in the following mail, leading Eric Dumazet to suggest
posting this on netdev.
In turn, this has been done just afterwards [1] so the issue is now
public. According to the linux-distros list policy, the original
reporter should also have made the issue public here, but failed to do
that.
I'm posting this right now in order to raise awareness for the
distributions already including 4.19 in a supported release.
As was discussed further on one of the threads on this topic, it looks
like this is a 4.20-rc issue only, and that 4.19 does not have this
issue. So it might not be relevant to any distro at all, but I suggest
that people test themselves to be sure.

thanks,

greg k-h
Yves-Alexis Perez
2018-11-23 20:45:24 UTC
Permalink
Post by Greg KH
As was discussed further on one of the threads on this topic, it looks
like this is a 4.20-rc issue only, and that 4.19 does not have this
issue. So it might not be relevant to any distro at all, but I suggest
that people test themselves to be sure.
Hi Greg, thanks for the precision.
- --
Yves-Alexis
Yves-Alexis Perez
2018-11-24 09:08:15 UTC
Permalink
Post by Yves-Alexis Perez
Post by Greg KH
As was discussed further on one of the threads on this topic, it looks
like this is a 4.20-rc issue only, and that 4.19 does not have this
issue. So it might not be relevant to any distro at all, but I suggest
that people test themselves to be sure.
Hi Greg, thanks for the precision.
And considering no released kernel is vulnerable, here is the proof of concept
code provided initially.

Regards,
--
Yves-Alexis
Dhiraj Mishra
2018-12-02 07:00:51 UTC
Permalink
Hey,

Just wanted to know is there any CVE assigned to this issue?



Thanks
Post by Yves-Alexis Perez
Post by Yves-Alexis Perez
Post by Greg KH
As was discussed further on one of the threads on this topic, it looks
like this is a 4.20-rc issue only, and that 4.19 does not have this
issue. So it might not be relevant to any distro at all, but I suggest
that people test themselves to be sure.
Hi Greg, thanks for the precision.
And considering no released kernel is vulnerable, here is the proof of concept
code provided initially.
Regards,
--
Yves-Alexis
--
Regards

*Dhiraj Mishra.*GPG ID : 51720F56 | Finger Print : 1F6A FC7B 05AA CF29
8C1C ED65 3233 4D18 5172 0F56
Wei Wu
2018-12-02 07:50:22 UTC
Permalink
hi,

there is none because it did not affect any release version.

wei
Post by Dhiraj Mishra
Hey,
Just wanted to know is there any CVE assigned to this issue?
Thanks
Post by Yves-Alexis Perez
Post by Yves-Alexis Perez
Post by Greg KH
As was discussed further on one of the threads on this topic, it looks
like this is a 4.20-rc issue only, and that 4.19 does not have this
issue. So it might not be relevant to any distro at all, but I
suggest
Post by Yves-Alexis Perez
Post by Greg KH
that people test themselves to be sure.
Hi Greg, thanks for the precision.
And considering no released kernel is vulnerable, here is the proof of concept
code provided initially.
Regards,
--
Yves-Alexis
--
Regards
*Dhiraj Mishra.*GPG ID : 51720F56 | Finger Print : 1F6A FC7B 05AA
CF29 8C1C ED65 3233 4D18 5172 0F56
Daniel Borkmann
2018-11-23 20:40:28 UTC
Permalink
Post by Greg KH
Post by Yves-Alexis Perez
Hi list,
we were notified on the Linux distros list of a vulnerability in the bpf
subsystem of the Linux kernel.
this was done in the following mail, leading Eric Dumazet to suggest
posting this on netdev.
In turn, this has been done just afterwards [1] so the issue is now
public. According to the linux-distros list policy, the original
reporter should also have made the issue public here, but failed to do
that.
I'm posting this right now in order to raise awareness for the
distributions already including 4.19 in a supported release.
As was discussed further on one of the threads on this topic, it looks
like this is a 4.20-rc issue only, and that 4.19 does not have this
issue. So it might not be relevant to any distro at all, but I suggest
that people test themselves to be sure.
Yep, 4.19 does not have this map type, so there is no released kernel
with this issue.

Thanks,
Daniel
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