339785 - scanner: memory exposure to scripts

Status: VERIFIED FIXED

(Core :: JavaScript Engine, defect)

Description

[Igor Bukanov]

The code of GetXMLEntity from jsscan.c contains the following code:

    bp = ts->tokenbuf.base + offset;
....
    FastAppendChar(&ts->tokenbuf, ';');
    bytes = js_DeflateString(cx, bp + 1,
                             PTRDIFF(ts->tokenbuf.ptr, bp, jschar) - 2);
 
This does not take into account that FastAppendChar may grow and reallocate the buffer. When such reallocation happens, ts->tokenbuf.ptr - bp can be an arbitrary number. If js_DeflateString can allocate and access the corresponding region of memory, bytes would be C string corresponding to this arbitrary number of characters. Then this string would be embedded in the throw error object that the script can catch and read.

Since in principle this could allow to read various bytes that travels through arena area via catching from script the thrown error object, I mark this as security problem.

Comment 1

[Igor Bukanov]

Attachment: Test case for JS shell

Note that depending on memory layout the test case may actually. If this is the case, try to change N in test() function to 127, 511 or other 2^p - 1 values.

Comment 2

[Igor Bukanov]

Attachment: Better test (for JS shell)

This is a better version as in the previous case that "must_be_good" string could be bad in fact.

Comment 3

[Igor Bukanov]

Attachment: Fix

The fix just remove appending of ';' to the buffer as it was not included in the error message in any case.

Comment 4

[Igor Bukanov]

I committed the fix

Comment 5

[Igor Bukanov]

Attachment: Even better test case

The test case now contains a loop to try various N itself.

Comment 6

[Brendan Eich [:brendan]]

Comment on attachment 223907 [details] [diff] [review]
Fix

Wow, what was I thinking?  Thanks,

/be

Comment 7

[Igor Bukanov]

I committed the patch to MOZILLA_1_8_BRANCH

Comment 8

[Daniel Veditz [:dveditz]]

Comment on attachment 223907 [details] [diff] [review]
Fix

approved for 1.8.0 branch, a=dveditz for drivers

Comment 9

[Igor Bukanov]

I committed the patch from comment 3 to MOZILLA_1_8_0_BRANCH

Comment 10

[Bob Clary [:bc] (inactive)]

Attachment: e4x/GC/regress-339785.js

Comment 11

[Bob Clary [:bc] (inactive)]

verified fixed 1.8.0.5, 1.8.1, 1.9a1 20060622 builds on all platforms.

Comment 12

[Bob Clary [:bc] (inactive)]

note to self: e4x/GC/regress-339785.js: TIMED OUT browser firefox-trunk-dbg-1.9a1_2006072314 windows, not seen on any other platform.

Comment 13

[Alexander Sack]

'Even better testcase' appeaers to be okay aviary. So I guess this is not present there. Igor?

Comment 14

[Igor Bukanov]

(In reply to comment #13)
> 'Even better testcase' appeaers to be okay aviary. So I guess this is not
> present there. Igor?
> 

The bug was introduces during 1.8 development. So assuming "aviary" means branches with version < 1.8, then the answer is that the bug does not exist there.

Comment 15

[Bob Clary [:bc] (inactive)]

/cvsroot/mozilla/js/tests/e4x/GC/regress-339785.js,v  <--  regress-339785.js