Closed Bug 969549 Opened 8 years ago Closed 8 years ago

Faulty: PCompositableTransaction reinterprets between layer types based on untrusted message params


(Core :: Graphics, defect)

Not set



Tracking Status
firefox28 --- wontfix
firefox29 --- wontfix
firefox30 + fixed
firefox-esr24 --- unaffected
b2g18 --- wontfix
b2g-v1.1hd --- wontfix
b2g-v1.2 --- wontfix
b2g-v1.3 --- wontfix
b2g-v1.3T --- wontfix
b2g-v1.4 --- fixed
seamonkey2.26 --- fixed


(Reporter: bjacob, Assigned: bjacob)


(Blocks 1 open bug)


(Keywords: sec-critical, Whiteboard: [adv-main30+][qa-])


(2 files)

Attached file Faulty session
Found by Christoph Diehl's "Faulty" fuzzer, see bug 777067

This is similar to bug 968833, but now for the PCompositableTransaction protocol.
Similar to bug 968833, I suggest sec-crit here. While the present faulty session gives a nice assert failure, that's because it was only calling a virtual method that turned out to be asserting on the current object type. Looking at CompositableTransactionParent.cpp there are places that static_cast between layer types based on untrusted inputs exactly like bug 968833.
To give just one example:

    case CompositableOperation::TOpPaintTextureRegion: {
      MOZ_LAYERS_LOG(("[ParentSide] Paint ThebesLayer"));

      const OpPaintTextureRegion& op = aEdit.get_OpPaintTextureRegion();
      CompositableParent* compositableParent = static_cast<CompositableParent*>(op.compositableParent());
      CompositableHost* compositable =
      ThebesLayerComposite* thebes =
Interesting bit in this Faulty log:

[Faulty] pickle field {int} of value: 8 changed to: 7

In CompositableType enum, 8 is COMPOSITABLE_IMAGE, 7 is BUFFER_TILED.
Blocks: 971262
hit an avatar of this in bug 971262.

Patch coming up.
Attachment #8374559 - Flags: review?(nical.bugzilla)
Attachment #8374559 - Flags: review?(nical.bugzilla) → review+
Assigning to bjacob because he has a patch.
Assignee: nobody → bjacob
Comment on attachment 8374559 [details] [diff] [review]

[Security approval request comment]
How easily could an exploit be constructed based on the patch?

Not easily. To someone with good understanding of our codebase (please send your resumes) the patch gives away that passing forged messages to PCompositorTransaction can result in unsafe memory accesses. It remains to figure how exactly to forge such messages (not hard, since it was found by fuzzing generic pickles) and how to actually exploit that (harder).

Do comments in the patch, the check-in comment, or tests included in the patch paint a bulls-eye on the security problem?


Which older supported branches are affected by this flaw?

All of them.

Do you have backports for the affected branches? If not, how different, hard to create, and risky will they be?

No backport ready, but wouldn't be difficult.

How likely is this patch to cause regressions; how much testing does it need?

Not very risky, but not trivial.
Attachment #8374559 - Flags: sec-approval?
Comment on attachment 8374559 [details] [diff] [review]

Attachment #8374559 - Flags: sec-approval? → sec-approval+
landed on central
Closed: 8 years ago
Flags: in-testsuite?
Resolution: --- → FIXED
Target Milestone: --- → mozilla30
v1.1 will be EOL on Monday, so it seems highly unlikely that this is going to be uplifted there :)
If we were going to backport these to 1.2 and 1.3, that time was a long time ago.
Whiteboard: [adv-main30+]
Marking [qa-] for desktop QA verification. FxOS QA may choose to verify at a later date.
Whiteboard: [adv-main30+] → [adv-main30+][qa-]
Applied cleanly to SeaMonkey 2.26.1 (Gecko 29-based)
Group: core-security
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