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Message-ID: <20190719140343.GA12952@thinkstation>
Date: Fri, 19 Jul 2019 07:03:43 -0700
From: Tavis Ormandy <taviso@...il.com>
To: oss-security@...ts.openwall.com
Subject: stack buffer overflow in fbdev
Hello, during a conversation on twitter we noticed a stack buffer
overflow in fbdev with malicious edid data:
https://github.com/torvalds/linux/blob/22051d9c4a57d3b4a8b5a7407efc80c71c7bfb16/drivers/video/fbdev/core/fbmon.c#L1033
There is enough space to have 52 1-byte length values, which makes svd_n
52, then make the final value length 0x1f (the maximum), which makes
svd_n 83 and overflows the 64 byte stack buffer svd[] with controlled
data.
This requires a malicious monitor / projector / etc, so pretty low impact.
I pulled out the code to make a demo (I removed the checksum, but it
doesnt prevent the bug):
https://gist.github.com/taviso/923776e633cb8fb1ab847cce761a0f10
This was discovered by Nico Waisman of Semmle.
Tavis.
--
-------------------------------------
taviso@....lonestar.org | finger me for my pgp key.
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