656752 - (CVE-2011-2367) WebGL crash [@gleRunVertexSubmitImmediate()]

Status: RESOLVED FIXED

(Core :: Graphics: CanvasWebGL, defect)

Description

[Christoph Diehl [:posidron]]

Attachment: testcase

Environment:

ProductName:	Mac OS X
ProductVersion:	10.6.7
BuildVersion:	10J869

OpenGL renderer string: NVIDIA GeForce GT 330M OpenGL Engine
OpenGL version string: 2.1 NVIDIA-1.6.26

and 

OpenGL renderer string: ATI Radeon HD 6750M OpenGL Engine
OpenGL version string: 2.1 ATI-1.6.32

Comment 1

[Christoph Diehl [:posidron]]

Attachment: callstack

Comment 2

[Benoit Jacob [:bjacob] (mostly away)]

Bingo: I can reproduce on Linux:
https://crash-stats.mozilla.com/report/index/a58d28f4-8125-447b-8ff8-39d102110516

That means it's almost certainly a bug in my code.

Comment 3

[Benoit Jacob [:bjacob] (mostly away)]

Seems to be that the WebGL state tracking code is getting confused into believing that there is an element array buffer bound (mBoundElementArrayBuffer is non-null) when there really isn't.

Comment 4

[Jeff Muizelaar [:jrmuizel]]

Seems like you might be able to use this to upload arbitrary data to the gpu and then extract it's contents.

Comment 5

[Benoit Jacob [:bjacob] (mostly away)]

Indeed... very scary.

Comment 6

[Benoit Jacob [:bjacob] (mostly away)]

Attachment: fix bindBuffer() bookkeeping

There you go: bindBuffer() was updating its bookkeeping before parameter validation was complete. The testcase was hitting a case where the bookkeeping was updated but the corresponding GL call was not performed, so the bookkeeping was no longer reflecting the actual GL state.

Comment 7

[Benoit Jacob [:bjacob] (mostly away)]

(In reply to comment #4)
> Seems like you might be able to use this to upload arbitrary data to the gpu
> and then extract it's contents.

Just for the record, here's how an attack could have proceeded, to implement PEEK:
1. set up vertex data (bound vertex buffers) so that the i-th vertex contains the value i.
2. set up a trivial vertex shader that just copies the vertex, and a fragment shader that encodes the vertex x-coord as color
3. reproduce the situation hit by Christoph's test case, call glDrawElements drawing 1 vertex as GL_POINTS, with an 'indices' parameter equal to some pointer you want to read the memory at.
4. now your rendered pixel's color tells you what was at this memory location

Comment 8

[Benoit Jacob [:bjacob] (mostly away)]

For sure we want this in Firefox 5.

What do we do for Firefox 4? Is this worth a chemspill?

Note, regarding comment 7: there's one little mitigation of the severity of this bug, it's that this pointer parameter gets validated as an index into a vertex array, so if it's greater than the length of currently bound arrays, it gets rejected. Of course that's not enough to make one feel comfortable.

Comment 9

[Benoit Jacob [:bjacob] (mostly away)]

Important: this bug has been open for 1 day before getting hidden.

Comment 10

[Benoit Jacob [:bjacob] (mostly away)]

Ugh, been open for 4 days actually.

Comment 11

[LegNeato]

Comment on attachment 532684 [details] [diff] [review]
fix bindBuffer() bookkeeping

Approved for mozilla-aurora

Comment 12

[Daniel Veditz [:dveditz]]

If we did a 4.0.x chemspill it might be worth it to take this fix.

Comment 13

[Sheila Mooney]

Can someone land this. We are soon going to merge over to Beta.

Comment 14

[Benoit Jacob [:bjacob] (mostly away)]

Landed on Mozilla-Aurora:

http://hg.mozilla.org/mozilla-aurora/rev/549dfefec7c0

But now I'm a bit scared: what if the bad guys are watching the logs?

Comment 15

[Benoit Jacob [:bjacob] (mostly away)]

Maybe I shouldn't land this on mozilla-central for now. In case the bad guys are watching only mozilla-central and not mozilla-aurora.

Comment 16

[Benoit Jacob [:bjacob] (mostly away)]

After discussion with Jeff and Ehsan, landed this on mozilla-central
http://hg.mozilla.org/mozilla-central/rev/db4ba8614fb6

Looking back at the patch, I find some relative comfort in the fact that it's only touching bindBuffer() and doesn't give away the clue that there was an exploit specifically with element array pointers i.e. the old OpenGL-1-ish signature of glDrawElements that's not supposed to be exposed by WebGL.

Comment 17

[Benoit Jacob [:bjacob] (mostly away)]

FIXED in firefox 5 and 6, but the question is still open for Firefox 4.