Re: CVE-2020-25656: Linux kernel concurrency UAF in vt_do_kdgkb_ioctl

                							

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Re: CVE-2020-25656: Linux kernel concurrency UAF in vt_do_kdgkb_ioctl

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From: Greg KH &lt;gregkh () linuxfoundation org&gt;

Date: Fri, 16 Oct 2020 09:03:49 +0200

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On Fri, Oct 16, 2020 at 08:58:34AM +0200, Jiri Slaby wrote:
Cc Greg.

On 16. 10. 20, 5:39, Minh Yuan wrote:
Hi,

We recently discovered a uaf read in vt_do_kdgkb_ioctl from linux kernel
version 3.4 to the latest version (v5.9 for now).

The root cause of this vulnerability is that there exits a race in
KDGKBSENT and KDSKBSENT.

Here are details:
1. use  KDSKBSENT to allocate a lager heap buffer to funcbufptr;
2. use KDGKBSENT to obtain the allocated heap pointer in step1 by
func_table, at the same time, due to KDGKBSENT has no lock, we can use
KDSKBSENT again to allocate a larger buffer than step1, and the old
funcbufptr will be freed. However, we've obtained the heap pointer in
KDGKBSENT, so a uaf read will happen while executing put_user.

Hi,

this is likely the issue I am fixing at:
https://git.kernel.org/pub/scm/linux/kernel/git/jirislaby/linux.git/commit/?h=devel&amp;id=57c85191e788e172a446e34ef77d34473cfb1e8d

I think, it won't apply cleanly as it's a part of a larger set. I will
reorder the patch and send something during the day.

Great, thanks for looking into this!

greg k-h

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Current thread:

CVE-2020-25656: Linux kernel concurrency UAF in vt_do_kdgkb_ioctl Minh Yuan (Oct 15)

&lt;Possible follow-ups&gt;
Re: CVE-2020-25656: Linux kernel concurrency UAF in vt_do_kdgkb_ioctl Jiri Slaby (Oct 16)

Re: CVE-2020-25656: Linux kernel concurrency UAF in vt_do_kdgkb_ioctl Greg KH (Oct 16)

 

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