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GC hazard with NoSuchMethod




JavaScript Engine
6 years ago
6 years ago


(Reporter: billm, Assigned: billm)




Firefox Tracking Flags

(firefox5+ fixed, firefox6+ fixed, status2.0 wanted, status1.9.2 unaffected)


(Whiteboard: [sg:critical?][fixed-in-tracemonkey][in-testsuite?])


(2 attachments)



6 years ago
Created attachment 528500 [details]

This script crashes in a shell with no jit options.
Whiteboard: [sg:critical?]

Comment 1

6 years ago
Created attachment 528630 [details] [diff] [review]

The basic problem is that the new object being allocated in js_OnUnknownMethod is the only thing that roots the method. This object is not scanned during a GC because it has a NULL shape, so it's treated as a newborn object. This was apparently sort of intentional, to ensure that these objects don't escape into user code. However, I think it's more important that we scan them.

I set the shape so that the object looks non-native, and then I added a trace hook to the class. I thought about making it a native object, but I think then we'd need a proto for it, and I didn't want to deal with that. Please correct me if I'm wrong, Jeff.
Assignee: general → wmccloskey
Attachment #528630 - Flags: review?(jwalden+bmo)
Comment on attachment 528630 [details] [diff] [review]

Sounds reasonable.
Attachment #528630 - Flags: review?(jwalden+bmo) → review+
Can this land now that it's reviewed n' all? Would this patch be safe for beta?
tracking-firefox5: --- → ?
tracking-firefox6: --- → ?

Comment 4

6 years ago
Sorry for the delay. I meant to land it yesterday but I forgot. I'll make sure it gets into the beta.

Comment 5

6 years ago

I pushed without the test. That needs to go in later.
Whiteboard: [sg:critical?] → [sg:critical?][fixed-in-tracemonkey][in-testsuite?]
cdleary-bot mozilla-central merge info:
Last Resolved: 6 years ago
Resolution: --- → FIXED


6 years ago
tracking-firefox5: ? → +
tracking-firefox6: ? → +
Attachment #528630 - Flags: approval-mozilla-beta+
status-firefox5: --- → fixed
This made it to mozilla-aurora as
status-firefox6: --- → fixed
On the 1.9.2 branch I get "TypeError: obj.x(a()) is not a function" rather than a crash. Does that mean that branch is not affected by this bug? Do we know what regressed it?
blocking1.9.2: --- → ?
status1.9.2: --- → ?

Comment 10

6 years ago
It looks like the testcase in the bug regressed in bug 584917, so 3.6 should be safe. Before that patch, we rooted the function to call via the NoSuchMethod object's parent (or proto, I forget the argument order).

I'm still a bit worried about whether the other thing stored in the NoSuchMethod object in rooted. It can only be a jsid, but it seems like e4x might somehow allow an object to be stashed there. I don't really understand the code too well though. It would be good if someone who understands e4x better could take a look. I'm guessing this means Brendan or Igor?
Thanks, for now we'll not track this on the old branch.
Blocks: 584917
blocking1.9.2: ? → ---
status1.9.2: ? → unaffected
status2.0: --- → wanted
Keywords: regression
Group: core-security
Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20100101 Firefox/6.0

Could you please provide some clear STR in order to verify this issue?
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