Last Comment Bug 8065 - crash on infinitely recursive frames site
: crash on infinitely recursive frames site
[nsbeta3-][TESTCASE] fix in hand
: crash, helpwanted, testcase
Product: Core
Classification: Components
Component: Layout: HTML Frames (show other bugs)
: Trunk
: All All
: P3 critical (vote)
: mozilla0.8
Assigned To: Eric Pollmann
: Chris Petersen
: Jet Villegas (:jet)
: 30013 31326 32389 34957 62541 63046 64020 110682 (view as bug list)
Depends on:
Blocks: 33722 51666
  Show dependency treegraph
Reported: 1999-06-13 00:59 PDT by AriB
Modified: 2002-10-29 11:37 PST (History)
8 users (show)
See Also:
Crash Signature:
QA Whiteboard:
Iteration: ---
Points: ---
Has Regression Range: ---
Has STR: ---

suggested patch (2.47 KB, patch)
2000-09-22 18:22 PDT, Eric Pollmann
no flags Details | Diff | Splinter Review
Test case 1 - iframes (83.74 KB, text/html)
2001-01-01 14:12 PST, Brian 'netdragon' Bober
no flags Details
test case 2 - Regular frames (.TAR File) (90.00 KB, application/octet-stream)
2001-01-01 14:14 PST, Brian 'netdragon' Bober
no flags Details

Description AriB 1999-06-13 00:59:00 PDT
Mozilla M6 (talkback) on a 450 mhz PII with 128 megs

APPRUNNER caused an invalid page fault in
module KERNEL32.DLL at 015f:bff9d709.
EAX=c002fb08 CS=015f EIP=bff9d709 EFLGS=00010212
EBX=00000000 SS=0167 ESP=0068fdf4 EBP=00690090
ECX=00000000 DS=0167 ESI=008b0f80 FS=18cf
EDX=780373c0 ES=0167 EDI=00403d90 GS=0000
Bytes at CS:EIP:
53 8b 15 dc 9c fc bf 56 89 4d e4 57 89 4d dc 89
Stack dump:
Comment 1 AriB 1999-06-13 02:07:59 PDT describes what's going on
Comment 2 don 1999-06-14 14:37:59 PDT
Chris, this appears to be an old bug that has plagued even previous versions of
ur browser ...
Comment 3 karnaze (gone) 1999-06-21 13:26:59 PDT
Eric, the only way to fix this bug is to implement a MAX_NUM_NESTED_FRAMES
concept. Currently, framesets don't even check for recursion and prevent it. The
max num idea would solve that problem as well. I'm not sure what the max should
be, possibly 100. This can be fairly easily implemented by going up the
nsWebShell parentage until the root is found. We may still want to check for
Comment 4 ekrock's old account (dead) 1999-06-23 19:47:59 PDT
My 2 cents: since previous browsers crashed on this too and it's a stupid kind
of page with no legitimate application, I would say that enhancing the browser
to catch this stop-me-before-I-shoot-myself edge case should be a lower priority
than fixing all other outstanding standards compliance bugs.  Unless it's
trivially easy for you to fix this, I recommend we mark it LATER and put our
energy elsewhere.  It *is* a crash, but if people deliberately set out to crash
the browser, they'll always find a way.  Let's focus on shipping a working 5.0
ASAP and postpone silly edge cases to 5.1.  Your final call based on time
required to fix.
Comment 5 leger 1999-12-22 13:47:59 PST
Moving [FEATURE] to Summary field for queries.
Comment 6 ekrock's old account (dead) 1999-12-22 21:23:59 PST
LATER. Stick this on the 5.1 stack. If people want to create HTML
pages that serve no function whatsoever than to deliberately crash the browser,
let 'em. All performance and standards support bugs are a higher priority than
this. We gotta start making tough decisions to ship the product, and this one
isn't even close to tough.
Comment 7 Chris Petersen 2000-01-06 12:36:59 PST
Marking verified later as per last comments.
Comment 8 Eric Pollmann 2000-03-08 22:49:17 PST
*** Bug 30013 has been marked as a duplicate of this bug. ***
Comment 9 Eric Pollmann 2000-03-10 14:57:19 PST
*** Bug 31326 has been marked as a duplicate of this bug. ***
Comment 10 Eric Pollmann 2000-04-09 18:11:48 PDT
*** Bug 34957 has been marked as a duplicate of this bug. ***
Comment 11 Eric Pollmann 2000-04-14 20:06:08 PDT
*** Bug 32389 has been marked as a duplicate of this bug. ***
Comment 12 John Morrison 2000-04-14 20:50:54 PDT
By the way Eric, earlier nav code flat out refuses to load a frame that 
points to itself (i.e., parent.location == SRC value of FRAME). 

The twist for this URL (above) is that it works around that rule by generating 
"unique" URLs for each descent. (That's why Chris notes above that the only 
complete solution is to test for some maximum number). 

I agree that this is not a high priority fix, but you might consider doing the 
'easy' fix for mozilla '1.0' -- just refuse to recur on an _identical_ URL.

Defer the MAX_NUM_NESTED_FRAMES fix for mozilla '1.1'.
Comment 13 Eric Pollmann 2000-04-14 22:18:57 PDT
John, just to play devil's advocate here, I can think of legitimate uses for 
*wanting* an iframe with the same URL as the containing page to load.

For example, in a server side script (CGI), I check the referrer and generate 
two different pages.  One if the referrer is someone else that contains an 
iframe with SRC=self.  Another if the referrer is myself that has some content 
in it without said iframe.

I might want to do something like this to ensure that people aren't able to link 
directly to (or directly contain) for example, an image on my site without also 
containing some explanatory text, for example, a copyright notice.

It is also possible that I might want to contain frames that have SRC=self and 
use cookies to keep track of what to display.  It seems arbitrary for us to 
*require* that a page author who wants to do such a thing or something similar 
generate a unique URL for each iframe or frame.

In other words, adding this kind of restriction, which is not in the standard, 
restricts functionality for the sake of preventing unreasonable behaviour if an 
author creates a logically flawed page.  

I think the right thing to do is enable the functionality and let careless 
authors suffer the consequences of creating such sites.  However, I still think 
we should limit stack depth to prevent crashes, of course.  :)

I think M18 is enough "later" for this...
Comment 14 John Morrison 2000-04-15 21:38:12 PDT
By the way, I'm not arguing that this is a high-priority (any time before
the last beta is good), but I do feel that closing off the simplest case (a
direct self-reference) is the right thing to do. [By direct self-reference I
mean a frame that points to a URL already visited by this frameset].

While there could be legitimate uses of this type of self-referencing /
recursion, I think that "in the wild" it is too easy for someone to shoot
themselves (or their audience) in the foot. [Aware programmers can always
use dummy query strings to work around the restriction on direct
self-reference, subject to an upper limit on depth as a safeguard against
bad logic].

This is especially true when, when in the absence of cookies (which is 
only a 'pref' away), HTTP is stateless. Combine that with any type of 
recursion, and that's not a good thing.

Yes, it's not in the standard, but it is documented legacy behaviour, at least 
in prior implementations of Navigator: 


 "Any frame that attempts to assign its SRC URL to be the same
  as the URL of any of its ancestors will be treated as if it
  has no SRC URL at all (basically a blank frame). While this
  doesn't stop all malicious documents, it eliminates a whole
  troublesome class of them."

Just a thought.
Comment 15 leger 2000-04-26 15:43:26 PDT
Adding crash keyword.
Comment 16 ekrock's old account (dead) 2000-05-05 22:34:10 PDT
<tough_decision>Even if Eric has the time to mess with this issue, those cycles
would be better spent fixing a bug from someone else's list which actually
affected real, valid content that was trying to do something legitimate (as
opposed to these bogus look-I-can-crash-your-browser pages that have to real
purpose). In the interest of shipping a high-quality FCS, it's vital that we
focus on real problems with real content. (e.g. Pulling a bug off of Troy's list
would be a much better use of time from the standpoint of helping real
customers.) Marking FUTURE and helpwanted. Eric, if we've fixed all the real
crashers, memory leaks, and semantic correctness bugs prior to FCS, let's
revisit this bug then. ;-> </tough_decision>
Comment 17 Blake Ross 2000-06-05 19:03:37 PDT
adding testcase kw
Comment 18 deneen 2000-06-29 11:35:08 PDT
I just thought I would point out that this works for iframes as well.

Comment 19 Eric Pollmann 2000-07-25 15:26:55 PDT
I have a fix for this.  It's small (~20 lines of code) does only a depth check, 
not a "circular reference" check.  This is a simple solution that does not limit 
functionality on most legitimate uses of recursion I can think of.  This fix is 
highly desirable because there are malicious people out there, and I'm imagining 
how ticked off I would be if I had just finished writing an epic email and 
clicked on a link that crashed the browser.

I chose a limit of 25 frames on the depth because Window NT starts failing 
trying to create widgets beyond a depth of 30 or so anyway.  The limit and the 
check only apply to content frames and not chrome, so recursive chrome can still 
bring the browser down.  Chrome should be coming from a trusted source and not 
do this silly kind of thing, right?  :)
Comment 20 Eric Pollmann 2000-07-25 15:31:49 PDT
Updating URL, platforms to All.  The testcase is internal, but is simply a 
series of pages of the form:

  <iframe src=page2.html>

Then page2 refers to page3, and so on.  I wrote a perl script to generate 100 
pages.  Would not recommend looking at these in IE, because it freezes.  ;)
Comment 21 Kevin McCluskey (gone) 2000-08-01 17:34:31 PDT
marking nsbeta3-
Comment 22 Jesse Ruderman 2000-09-11 03:58:35 PDT
is it the depth or the high number of webshells that's making mozilla crash?
Comment 23 Ben Bucksch (:BenB) 2000-09-22 17:46:04 PDT
I am surprised, that securing the browser against Denial-Of-Service attacks has
such a low priority on the managers' list. Eric, do you have a review and the
module owner ok?
Comment 24 Eric Pollmann 2000-09-22 17:58:46 PDT
Jesse - not sure, but I think it is the depth that causes problems.  I've seen
pages that have 100 web shells (10x10 frameset) with depth 1 load with no

Ben - true - this is an easy fix, but not completely without risk.  There are
some minor performance implications, and this could make sites that have depth
greater than MAXDEPTH (25) stop working (though I've never seen sites with depth
more than 4 or so).

I am the closest thing to module owner for framesets, so that' okay - haven't
gotten a review or super-review because this wasn't nsbeta3+ approved.  If you
would like to open this bug for reconsideration by the PDT team please remove
the nsbeta3- from the status whiteboard.

I'll attach my fix for review if anyone wants to look at it.
Comment 25 Eric Pollmann 2000-09-22 18:22:25 PDT
Created attachment 15373 [details] [diff] [review]
suggested patch
Comment 26 Boris Zbarsky [:bz] (still a bit busy) 2000-12-20 00:41:14 PST
*** Bug 62541 has been marked as a duplicate of this bug. ***
Comment 27 Boris Zbarsky [:bz] (still a bit busy) 2000-12-20 00:41:42 PST
*** Bug 63046 has been marked as a duplicate of this bug. ***
Comment 28 Boris Zbarsky [:bz] (still a bit busy) 2000-12-20 00:45:53 PST
Adding 4xp keyword, since NS 4.7 has no trouble with the pages from bug 63046
and bug 62541
Comment 29 Kevin McCluskey (gone) 2000-12-20 14:34:47 PST
Set milestone to mozilla0.9.
Eric if the patch doesn't work, mark this bug future.
Comment 30 Keyser Sose 2000-12-31 17:35:56 PST
*** Bug 64020 has been marked as a duplicate of this bug. ***
Comment 31 Brian 'netdragon' Bober 2001-01-01 14:12:43 PST
Created attachment 21536 [details]
Test case 1 - iframes
Comment 32 Brian 'netdragon' Bober 2001-01-01 14:14:28 PST
Created attachment 21537 [details]
test case 2 - Regular frames (.TAR File)
Comment 33 Brian 'netdragon' Bober 2001-01-01 14:44:38 PST
This is a parity bug (and a source of possible embarrasment) since MSIE5 
doesn't have a problem with these kinds of pages.

Unfortunately, I just realized due to Bugzilla renaming the file that Test Case 
1 will have to be saved to your hard drive and named as "Testcase2.html".
The testcases are to have a local-to-the-bug source for testing this. I put a 
lot of text in them so they will cause memory bloat at a very rapid rate. If 
you look at my testcases, you will see that a MAX_NESTED_FRAMES of 25 might be 
too much. I recommend determining it by the amount of memory used. The 
innermost frame can say something like "Error: Too many nested frames"

To build off Eric Pollman's devil advocacy, I would like to say that nested 
frames can be implemented in a way that is useful with javascript. For 
instance, for displaying the contents of a tree structure with javascript. 
Comment 34 Ben Bucksch (:BenB) 2001-01-01 17:17:34 PST
Shortening SUMMARY.
Comment 35 Eric Pollmann 2001-01-12 16:38:07 PST
Thanks for the test cases!

I just tested again on Windows.  The patch works fine with both of the above
testcases.  The reason it was not checked in earlier was that it didn't recieve

Test case 1:
  NS6 release: memory usage grows unbounded. (I gave up at 151MB)
    After 30 levels deep, WinNT just stops showing further nested windows.
  Debug Moz with fix: memory grows but stops at 50.6MB
    The nesting is limited to 25 levels deep, rendering is very similar to what
    the unbounded test case looks like, but it stops just before shooting itself
    in the foot.  :)

Test case 2:
  NS6 release: memory usage grows unbounded. (I gave up at 151MB)
    After 30 levels deep, WinNT just stops showing further nested windows.
  Debug Moz with fix: memory grows but stops at 42.8MB
    The nesting is limited to 25 levels deep, rendering is identical to what
    the unbounded test case looks like, but it stops just before shooting itself
    in the foot.  :)

40-50MB of memory usage seems somewhat reasonable to me, as this is an edge case
- at any rate, it's certainly more reasonable than growing unbounded, infinite
looping, and eventually crashing the browser.

Will get r= and sr= for this bug.
Comment 36 Eric Pollmann 2001-02-05 16:53:26 PST
Fix checked in.  To verify, view either of the to attached test cases.  The
browser should not crash.
Comment 37 John Morrison 2001-02-05 18:14:24 PST
Er, Eric ... you excluded XUL frames from this check? Is that correct? Why
would that be the case.
Comment 38 Eric Pollmann 2001-02-05 18:57:22 PST
> Er, Eric ... you excluded XUL frames from this check? Is that correct?
> Why would that be the case.

I excluded chrome from this check, which is a little different than XUL per se -
but the reason was pretty simple:

I think the 99% case for this bug is a user viewing a random page, and the
author of that page has done something accidental or malicious (recursive
frames) that could cause the browser to crash.  We don't want that.

However, that must be weighed against allowing the browser to be a flexible,
powerful, and consistent as possible.  Basically, I wanted to allow for complex
chrome around the browser window - and not have that affect the depth to which
content you are viewing is nested arbitrarily.

And chrome is, by definition, trusted content - capable far more malicious
things than just making the browser crash!
Comment 39 John Morrison 2001-02-05 20:14:18 PST
> I excluded chrome from this check, which is a little different than 
> XUL per se - but the reason was pretty simple:

Ah. So, XUL over HTTP is subject to this check. Yes? (i.e. a random, malicious,
web page can't serve crashing content by using XUL instead of HTML).
Comment 40 Brian 'netdragon' Bober 2001-02-05 21:27:42 PST
Eric: Better than before. Congragulations. Unfortunately, I still see a 
problem. When running testcase 1,  Mozilla bloated to 64 Megs before I had to 
end-task it. It brought my system to a stand-still. I agree that the nested 
frames end finally, but not soon enough in this case. I have an "average" 
system. A PII Laptop with Win2k and 128 Meg of Ram (but only 400 megs free hd). 
I finally got a message that Virtual Mem is too low (around 400 megs vm). I 
think that there should be a memory limit as opposed to a nesting limit. IE: If 
a page is, say, 80K and takes up 200K of mem when parsed and calls itself 
recursively, and the user has 100MB of virtual mem left, then maybe Mozilla can 
take up 2% total mem for that page. Therefore, 2MB can be used. That equals 10 
times before stopping. I prefer a more ambitious theme such as this than to 
just putting a number limit.

Also, another thing that bothered me was that it gave no message such 
as "Infinitely recursive frames will be rendered no further".
Comment 41 Brian 'netdragon' Bober 2001-02-05 21:28:55 PST
Sorry for the spam. Eric: Do you think you can reopen this and change the 
summary to "Memory bloat on infinitely recursive frames"? Or should a seperate 
bug be filed?
Comment 42 Eric Pollmann 2001-02-05 22:17:52 PST
> Ah. So, XUL over HTTP is subject to this check. Yes? (i.e. a random,
> malicious, web page can't serve crashing content by using XUL instead of
> HTML).

I don't think I know enough about XUL to answer your question definitively, but
my guess is that this fix does NOT prevent an author from creating a recursive
XUL page that might crash the browser - though I'm not sure of all the specifics
on how one might do that.  The check I put in was specific to the frame that is
used to display HTML framesets and iframes.  Can you create an example?

Brian, you mention two different, but very important points:

1) This fix was merely to address the crash, it doesn't try to calculate memory
usage.  (To be fair, I think you might be underestimating the complexity of such
a change.  First, we would need to calculate free memory (in a platform
independent way so that it would work on Windows 98, Mac, Linux, Win NT,
Solaris, ...  Second, we would need to somehow magically know that our user was
okay with 2% of memory use per document, and that we should only limit it to
this if the reason for excess was due to nesting of a frameset.)

I believe there may be ongoing work to address this at an architectural level
with a "memory pressure" scheme, where a global notification will be made when a
low memory condition exists, and anyone listening to this notification will then
purge excess data (flush caches, ...).

However, suggestions are more than welcome - if you think this might be better
to handle as a special case for framesets, please feel free to file a bug
(probably better as a separate issue)

2) No error message is reported to the user if we truncate frameset nesting.

This should probably be filed as an enhancement request - with suggestions for
the UI (do you think a dialog box would work?  too invasive?  Should the
innermost document display a message?)
Comment 43 John Morrison 2001-02-05 22:36:23 PST
Actually, since a xul <iframe> derives its implementation directly from 
the HTML iframe, I think that this might be fixed. 

Simple example is :

----save as c:\temp\file.xul (or other OS path) ----

<?xml version="1.0"?> 
<?xml-stylesheet href="chrome://global/skin" type="text/css"?>
<window id="main-window" xmlns:html=""
    <text value="hello, goodbye, hello"/>
    <iframe style="border:2px solid red;" 
            src="file:///c:/temp/file.xul" flex="100%"/>
    <text value="hello, goodbye, hello"/>

Comment 44 Ben Bucksch (:BenB) 2001-02-06 03:25:07 PST
Pollmann, thanks for creating the fix and checking it in. IMO, the fix of
limited to a certain number of nesting levels is just fine. If an attacker wants
to, he can create large pages in other ways as well - memory shortage and
related DoSes are a separate problem.

> Mozilla bloated to 64 Megs

That's just fine, isn't it? Mailnews can grow larger in normal operation...

> Virtual Mem is too low (around 400 megs vm)

What now? 400MB or 64MB(+system)?
Comment 45 Brian 'netdragon' Bober 2001-02-06 17:13:01 PST
Eric. I didn't mean to attack your code. You did solve the bug. I just wanted 
to mention something again that I had mentioned earlier. I don't know if people 
saw it the first time.
Comment 46 Brian 'netdragon' Bober 2001-02-06 17:14:41 PST
Mozilla does really need some memory control, but I guess that is a seperate 
Comment 47 Chris Petersen 2001-03-01 11:45:59 PST
Fixed in the Feb 28th build.
Comment 48 Brian 'netdragon' Bober 2001-03-03 23:36:51 PST
See also bug 70821 about adding the ability to limit memory usage per browser 
Comment 49 Boris Zbarsky [:bz] (still a bit busy) 2001-11-18 11:36:22 PST
*** Bug 110682 has been marked as a duplicate of this bug. ***

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