pixman image ref-counting races with cairo solid colors

RESOLVED FIXED in Firefox 47

Status

()

RESOLVED FIXED
3 years ago
2 years ago

People

(Reporter: karlt, Assigned: karlt)

Tracking

(Blocks: 1 bug, {csectype-uaf, regression, sec-high})

32 Branch
mozilla49
csectype-uaf, regression, sec-high
Points:
---
Dependency tree / graph
Bug Flags:
qe-verify -

Firefox Tracking Flags

(firefox46 wontfix, firefox47+ fixed, firefox48+ fixed, firefox49+ fixed, firefox-esr4547+ fixed)

Details

(Whiteboard: [post-critsmash-triage][adv-main47+][adv-esr45.2+])

Attachments

(2 attachments)

(Assignee)

Description

3 years ago
https://cgit.freedesktop.org/cairo/commit/?id=71e8a4c23019b01aa43b334fcb2784c70daae9b5
https://bugs.freedesktop.org/show_bug.cgi?id=

pixman_image_t has virtual function pointers, making use after free serious, but triggering the race is likely difficult.
(Assignee)

Comment 1

3 years ago
Created attachment 8753596 [details]
debug session highlights
(Assignee)

Updated

3 years ago
Blocks: 994541, 1268202
Keywords: regression
(Assignee)

Updated

3 years ago
OS: Unspecified → All
Hardware: Unspecified → All
(Assignee)

Comment 2

3 years ago
Created attachment 8753622 [details] [diff] [review]
don't reuse pixman images when not thread-safe

https://treeherder.mozilla.org/#/jobs?repo=try&revision=f064f419ca59
Attachment #8753622 - Flags: review?(jmuizelaar)
Group: core-security → gfx-core-security
Attachment #8753622 - Flags: review?(jmuizelaar) → review+
(Assignee)

Comment 3

3 years ago
Comment on attachment 8753622 [details] [diff] [review]
don't reuse pixman images when not thread-safe

[Security approval request comment]
> How easily could an exploit be constructed based on the patch?
Difficult but conceivable.  An increment needs to be run concurrently with a decrement and these can only happen on main and compositor threads afaik.
Content would need to control the content of an allocation very soon after the refcount decrement, but that could be done on a worker thread.  The |cache| variable provides opportunity to retry continually until success.

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

> Which older supported branches are affected by this flaw?
All of them.

> If not all supported branches, which bug introduced the flaw?
Bug dates back to bug 562746 at least.

> Do you have backports for the affected branches? If not, how different, hard to create, and risky will they be?
The code has not changed much so backports are not difficult.

> How likely is this patch to cause regressions; how much testing does it need?
Unlikely.  It just removes some reuse of objects, instead now creating a new object each time.
Attachment #8753622 - Flags: sec-approval?
(Assignee)

Comment 4

3 years ago
(In reply to Karl Tomlinson (ni?:karlt) from comment #3)
> [Security approval request comment]
> > If not all supported branches, which bug introduced the flaw?
> Bug dates back to bug 562746 at least.

Sorry, that's not correct.  The bug was introduced with OMTC, bug 899785.
Blocks: 899785
sec-approval+ for trunk. I'd like to get a patch nominated for Aurora, Beta, and ESR45 as well.
status-firefox46: --- → wontfix
status-firefox47: --- → affected
status-firefox48: --- → affected
status-firefox49: --- → affected
status-firefox-esr45: --- → affected
tracking-firefox47: --- → ?
tracking-firefox48: --- → +
tracking-firefox49: --- → +
tracking-firefox-esr45: --- → ?
Attachment #8753622 - Flags: sec-approval? → sec-approval+
(Assignee)

Comment 6

3 years ago
Comment on attachment 8753622 [details] [diff] [review]
don't reuse pixman images when not thread-safe

Approval Request Comment
[Feature/regressing bug #]:
Bug 899785.
[User impact if declined]:
Random crash (bug 1268202), potentially exploitable.
[Describe test coverage new/current, TreeHerder]:
No new test.  Exploiting the race would require careful timing or brute force.
Code is widely used and so exercised by existing tests.
[Risks and why]: 
Unlikely.  The patch just removes some reuse of objects, instead now creating a new object each time.
[String/UUID change made/needed]:
None

[Approval Request Comment]
Fix Landed on Version: 49
Attachment #8753622 - Flags: approval-mozilla-esr45?
Attachment #8753622 - Flags: approval-mozilla-beta?
Attachment #8753622 - Flags: approval-mozilla-aurora?

Comment 8

3 years ago
Comment on attachment 8753622 [details] [diff] [review]
don't reuse pixman images when not thread-safe

Sec-high, Aurora48+, Beta47+, ESR45+
Attachment #8753622 - Flags: approval-mozilla-esr45?
Attachment #8753622 - Flags: approval-mozilla-esr45+
Attachment #8753622 - Flags: approval-mozilla-beta?
Attachment #8753622 - Flags: approval-mozilla-beta+
Attachment #8753622 - Flags: approval-mozilla-aurora?
Attachment #8753622 - Flags: approval-mozilla-aurora+

Updated

3 years ago
tracking-firefox47: ? → +
tracking-firefox-esr45: ? → 47+
https://hg.mozilla.org/releases/mozilla-beta/rev/256e89214e18
status-firefox47: affected → fixed
https://hg.mozilla.org/mozilla-central/rev/fb131a07c5bc
Status: ASSIGNED → RESOLVED
Last Resolved: 3 years ago
status-firefox49: affected → fixed
Resolution: --- → FIXED
Group: gfx-core-security → core-security-release
Flags: qe-verify-
Whiteboard: [post-critsmash-triage]
Whiteboard: [post-critsmash-triage] → [post-critsmash-triage][adv-main47+][adv-esr45.2+]
Version: unspecified → 32 Branch
Group: core-security-release
You need to log in before you can comment on or make changes to this bug.