455987 - integer overflow in nsEscape

Status: RESOLVED FIXED

(Core :: XPCOM, defect, P1)

Description

[Daniel Veditz [:dveditz]]

+++ This bug was initially created as a clone of Bug #445117 +++

>  /* XXX Hardcoded max entity len. The +1 is for the trailing null. */
>  char *rv = (char *) nsMemory::Alloc(strlen(string) * 6 + 1);
>
> |* 6| overflows at about 683M on 32 bit platform.

The issue Georgi noted in bug 445117 also occurs in xpcom/io/nsEscape.cpp -- the same pattern happens in nsEscapeHTML() and nsEscapeHTML2()

I'm not sure if you can practically stuff 683M into the things that use nsEscapeHTML, maybe if the transport is gzipped.
http://mxr.mozilla.org/mozilla/search?string=nsEscapeHTML

Comment 1

[georgi - hopefully not receiving bugspam]

dveditz you mean something different from Bug 367736 ?

Comment 2

[georgi - hopefully not receiving bugspam]

aaa, i see:
http://mxr.mozilla.org/mozilla-central/source/xpcom/io/nsEscape.cpp#292

292   PRUnichar *resultBuffer = (PRUnichar *)nsMemory::Alloc(aSourceBufferLen *
293                             6 * sizeof(PRUnichar) + sizeof(PRUnichar('\0')));

Comment 3

[georgi - hopefully not receiving bugspam]

>I'm not sure if you can practically stuff 683M

i suppose receiving it is possible.

more of problems for exploiting this probably are:

1. 683 MB on the wire consumes much more VM so OOM may be hit
2. one must avoid crash. though if one does overlapping copy (the returned ptr is in low address) it may not crash.

Comment 4

[georgi - hopefully not receiving bugspam]

in theory 683MB need not be on the wire - they may be javascript generated probably

Comment 5

[Daniel Veditz [:dveditz]]

Yeah, a document title in places, say, or something fed through the feed sanitizer.

Comment 6

[Daniel Veditz [:dveditz]]

This code got copied to nsPlacesImportExportService.cpp, apparently because the use of string apis in the nsEscape copy caused problems?

http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/browser/components/places/src/nsPlacesImportExportService.cpp&rev=1.65#239

Dietrich: what's the story there? Is the situation different now so this code can call the standard escape routine? Simple enough to fix in both places, but if it's no longer necessary getting rid of duplicate code would be nice.

Comment 7

[Daniel Veditz [:dveditz]]

Attachment: prevent nsEscapeHTML overflow

In addition to the patch I cleaned up a bunch of tabs. Will attach a -w patch next to make review easier.

Comment 8

[Daniel Veditz [:dveditz]]

Attachment: cvs diff -w version of above

Comment 9

[Daniel Veditz [:dveditz]]

Attachment: same for places

Comment 10

[Benjamin Smedberg]

Comment on attachment 344247 [details] [diff] [review]
prevent nsEscapeHTML overflow

>Index: xpcom/io/nsEscape.cpp

>+    char *rv = nsnull;
>+    /* XXX Hardcoded max entity len. The +1 is for the trailing null. */
>+    PRUint32 len = PL_strlen(string);
>+    if (len < (PR_UINT32_MAX / 6)) {
>+        rv = (char *)nsMemory::Alloc( (len * 6) + 1 );
>+    }
>+    char *ptr = rv;
> 
>-	return(rv);
>+    if(rv)

This would be a lot clearer if you took a shortcut path:

  if (len >= PR_UINT32_MAX / 6)
    return nsnull;

  char *rv = (char*) NS_Alloc((6 * len) + 1);
  if (!rv)
    return nsnull;

  ... conversion code

This reduces the overall indent and makes the control flow more apparent.

Also please use NS_Alloc instead of nsMemory::Alloc in all new code.

r=me with those nits addressed

Comment 11

[Daniel Veditz [:dveditz]]

Attachment: nits fixed, what was checked in

Comment 12

[Daniel Veditz [:dveditz]]

Attachment: diff -w version of the above

Comment 13

[Daniel Veditz [:dveditz]]

checked in: http://hg.mozilla.org/mozilla-central/rev/c6d4904201b5

Comment 14

[Samuel Sidler (old account; do not CC)]

Comment on attachment 344700 [details] [diff] [review]
nits fixed, what was checked in

Approved for 1.8.1.18 and 1.9.0.4. a=ss

Comment 15

[Daniel Veditz [:dveditz]]

Checked into the 1.8 and 1.9.0 branches

Comment 16

[Al Billings [:abillings - ex-MoCo]]

Any word on a mechanism to exercise this code as we discussed the other day, Dan?

Comment 17

[Alexander Sack]

Comment on attachment 344700 [details] [diff] [review]
nits fixed, what was checked in

a=asac for 1.8.0 branch

Comment 18

[Benjamin Smedberg]

This landed before 1.9.1 branched