SKIA ICO decoding information leak

[GoogleCodeExporter]

The SKIA image decoder for the ICO file format has an out-of-bounds read 
condition that can lead to a pixel-based information leak. Depending on how the 
SKIA library is used, this could lead to ASLR bypass attacks, or direct 
information leak attacks (i.e. exfiltrating sensitive data from the victim's 
heap to an attacker in some manner). 

The following code snippet is from SkICOImageDecoder::onDecode 
(skia/src/images/SkImageDecoder_libico.cpp):

...
    const size_t size = read4Bytes(buf, 14);
    const size_t offset = read4Bytes(buf, 18);

    if (offset > length || size > length || ((uint64_t)offset + size) > length) {
        return kFailure;
    }

    {   
        SkMemoryStream subStream(buf + offset, size, false);
        SkAutoTDelete<SkImageDecoder> otherDecoder(SkImageDecoder::Factory(&subStream));
        if (otherDecoder.get() != NULL) {
            ...
        }
    }
...
    int bitCount = read2Bytes(buf, offset+14);
...
    int begin = SkToInt(offset + 40);

Note that the offset field can be set to a value that is in bounds when 
compared to "length", but is out of bounds when a constant is added to it (e.g. 
40 in the case of "begin").

This can lead to pixel data being read from out-of-bounds heap memory that is 
adjacent to the input buffer. An example of this behavior in an Android 
application (running on AOSP master, displaying to an ImageView after being 
converted to a Bitmap) is attached (ico_leak01.jpg). The crafted ICO file that 
triggers this condition is also attached (ico_leak01.ico).

This issue should be fixed by checking that all arithmetic performed on the 
supplied "offset" value is in bounds with respect to "length".

This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.

Original issue reported on code.google.com by haw...@google.com on 6 Feb 2015 at 1:17

Attachments:

• ico_leak01.ico
• ico_leak.jpg

[GoogleCodeExporter]

Fixed in https://codereview.chromium.org/996173005

Original comment by haw...@google.com on 13 Mar 2015 at 6:58

• Changed state: Fixed

[GoogleCodeExporter]

Original comment by haw...@google.com on 25 Mar 2015 at 12:47

• Removed labels: Restrict-View-Commit