Re: [CVE-2020-14331] Linux Kernel: buffer over write in vgacon_scrollback_update

                							

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Re: [CVE-2020-14331] Linux Kernel: buffer over write in vgacon_scrollback_update

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From: Eric Biggers &lt;ebiggers () kernel org&gt;

Date: Tue, 28 Jul 2020 11:59:14 -0700

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On Tue, Jul 28, 2020 at 11:16:55AM +0800, 张云海 wrote:
There is a buffer over write in drivers/video/console/vgacon.c in
vgacon_scrollback_update.

The issue is reported by Yunhai Zhang / NSFOCUS Security Team
&lt;zhangyunhai () nsfocus com&gt;, CVE-2020-14331 assigned via Red Hat.

# Affected Versions
The issue is found and tested on 5.7.0-rc6.
The issue is introduced in commit:
15bdab959c9bb909c0317480dd9b35748a8f7887 ([PATCH] vgacon: Add support
for soft scrollback)
According to code review, all versions older than
92ed301919932f777713b9172e525674157e983d (v5.8-rc7) are affected.

Thanks for the writeup.  Note that there are many open syzbot reports in the
fbdev, vt, and vgacon kernel subsystems.  These subsystems aren't actively
maintained (receiving drive-by fixes only), and the kernel developers recommend
to not enable these subsystems if you care about security
(https://lkml.kernel.org/lkml/CAKMK7uF5zZH3CaHueWsLR96-AzT==wP8=MpymTqx-T+SRsXWHA () mail gmail com/).

This particular bug, for example, appears to have been already found by someone
running syzkaller and publicly reported over 2 years ago, with a C reproducer:
(https://lkml.kernel.org/lkml/CAEAjamsJnG-=TSOwgRbbb3B9Z-PA63oWmNPoKYWQ=Z=+X49akg () mail gmail com/).
No one did anything.

I suggest that people relying on the security of these kernel subsystems
contribute resources to fixing the many known fuzzing bugs in them.

- Eric

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Current thread:

[CVE-2020-14331] Linux Kernel: buffer over write in vgacon_scrollback_update 张云海 (Jul 28)

Re: [CVE-2020-14331] Linux Kernel: buffer over write in vgacon_scrollback_update Eric Biggers (Jul 28)

Re: [CVE-2020-14331] Linux Kernel: buffer over write in vgacon_scrollback_update Solar Designer (Jul 29)

Re: [CVE-2020-14331] Linux Kernel: buffer over write in vgacon_scrollback_update 张云海 (Jul 30)

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