Hi Jay,
You still don't check the read() calls in the length case to see if you
reached EOF (-1). The potential for an infinite loop is still there.
Also, you still search for an FF, even if you require the function to
start at an SOI marker - all subsequent markers are still subject to a
search rather than a deterministic requirement that we encounter markers
with no gaps between them.
Why do we have the foundFF variable in the first place? If we just saw
an SOI marker then the next byte *must be* a 0xff (shouldn't it? Am I
missing something?). We shouldn't read a byte and check if it is a 0xff
and then try again, we should expect a single 0xff byte followed by a
marker type byte, as in:
while (true) {
int byteval == iis.read();
// if (byteval < 0) then what?
if (byteval != 0xff) { exception }
byteval = iis.read();
switch (byteval) {
}
}
The only question is if we get a -1 on the first read if we treat that
as an implicit EOI as we do now, or if we treat it as an exception.
Note that if we get a -1 in the second read, then we have a half-formed
tag and that should fall into the default and be declared a bad file.
...jim
On 6/13/2016 10:00 AM, Jayathirth D V wrote:
Hi Jim,
Thanks for your valuable inputs.
I have updated the code with your inputs:
1) We should check for complete SOI marker and not just "FF" at start
of skipImage().
2) There is no need of iis.read() which was happening in default case.
iis.read() present in for loop check will take care of checking EOF.
3) I have added case condition for all the markers having length and
added default case where we get invalid marker starting with FF.
Apart from above changes, after going more through
https://www.w3.org/Graphics/JPEG/itu-t81.pdf got to know following things:
1) TEM is also one more marker without length so added case for that.
2) Since we have all unique conditions checked, we should not find any
SOI marker after the initial SOI marker before we find EOI. Made changes to
throw IOException in this case.
Please find updated webrev for review:
http://cr.openjdk.java.net/~jdv/8152672/webrev.01/
Thanks,
Jay
-----Original Message-----
From: Jim Graham
Sent: Saturday, June 11, 2016 3:07 AM
To: Jayathirth D V; Philip Race
Cc: 2d-dev@openjdk.java.net
Subject: Re: [OpenJDK 2D-Dev] Review Request for JDK-8152672 : Exception while
getting second image properties for JPEG with embedded thumbnail
Thanks for the response Jay, I think I was misreading some of the code as now
that I look back at it, it's mostly written as I was suggesting with respect to
skipping over data sections, however it is still doing some scanning to find
the initial 0xFF. Some thoughts:
- If we can be sure that we are located at where a tag should be, then
shouldn't we just read a byte and assert that it is 0xFF and report the file as
invalid if it isn't? The current code will just ignore the byte and continue
reading until it finds a 0xFF, but the fact that the first byte we read isn't
0xFF means we have wandered into data that isn't following the file format (or,
possibly, that this was called from a case where we hadn't completely read a
section of data, but that should be fixed as we could be in the middle of a
section that isn't entropy encoded and our search for 0xFF might have invalid
assumptions).
- The bytes read in the default section to get the length and the tag for the
next block aren't tested for EOF (-1). This may even get us into an infinite
loop if we hit EOF at the right time (just after a sized block tag) as the size
bytes will read and combine into a -1 size, back up three bytes, and then
reread the same tag and try to compute a length again which will send us back 3
bytes, etc.
- default assumes that all other markers that are created will be sized, but
can we assert that? Shouldn't we specifically list all known sized markers and
have the default case reject the file as not being of a format that we
recognize?
...jim
On 6/9/2016 11:21 PM, Jayathirth D V wrote:
Hi Jim,
I think the harmless byte that you are referring to will be applied only for image data(Between
SOS(Start of Scan) marker and EOI). For example, any "FF" data present in Jpeg image will
be represented as "FF 00". But I think application headers or comments section can
contain data which will be similar to EOI,SOI or other markers(FF XX).
Thanks,
Jay
-----Original Message-----
From: Jim Graham
Sent: Friday, June 10, 2016 5:28 AM
To: Jayathirth D V; Philip Race
Cc: 2d-dev@openjdk.java.net
Subject: Re: [OpenJDK 2D-Dev] Review Request for JDK-8152672 :
Exception while getting second image properties for JPEG with embedded
thumbnail
It looks like JPEG files have protection for scanning for an FF and assuming it
is a marker by making sure that all FF bytes that appear in data are followed
by a harmless byte, so a brute force search is probably fine. But it still
seems wasteful when we know we are at a tag and we know the sizes of all of the
tags, we should be able to skip around the file looking for the SOI directly...
...jim
On 6/2/2016 5:10 AM, Jayathirth D V wrote:
Fixed typo.
*From:*Jayathirth D V
*Sent:* Thursday, June 02, 2016 5:08 PM
*To:* Philip Race
*Cc:* Jim Graham; 2d-dev@openjdk.java.net
*Subject:* RE: Review Request for JDK-8152672 : Exception while
getting second image properties for JPEG with embedded thumbnail
Hi Phil,
We have two kind of images with which we are able to reproduce the issue:
1) sample.jpg present in JBS bug(We can't use this image because it
is licensed ).
2) JpegEmbedThumbnail.jpg taken using Prasanta's camera and used in
webrev.
_ _
_sample.jpg : _
_ _
If we do getNumImages() it will return 2. getNumImages() follows the
same logic of skipping markers with length and registering SOI to get
number of images.
sample.jpg has markers as follows :
SOI -> APP1 - > SOI -> EOI -> APP1 End -> EOI -> SOI -> EOI
I have dumped first image its SOI is first one in the above list and
for second image it is third one in the list. getNumImages() counts
first and third SOI for number of images. But in case of skipImage()
we are getting inside APP1 marker and considering its SOI.
_JpegEmbedThumbnail.jpg :_
_ _
If we do getNumImages() it will return 1.
JpegEmbedThumbnail.jpg has markers as follows :
SOI -> APP1 -> SOI -> EOI -> APP1 End -> APP2 -> SOI -> APP2 End ->
APP2
-> EOI -> APP2 End -> EOI
getNumImages() counts only first SOI for number of images. But in
case of skipImage() we will are getting inside APP1 and APP2 markers also.
Thanks,
Jay
*From:*Phil Race
*Sent:* Thursday, June 02, 2016 4:05 AM
*To:* Jayathirth D V
*Cc:* Jim Graham; 2d-dev@openjdk.java.net
<mailto:2d-dev@openjdk.java.net>
*Subject:* Re: Review Request for JDK-8152672 : Exception while
getting second image properties for JPEG with embedded thumbnail
I am bit doubtful about this. Are you sure we are correct in
reporting two images to begin with ?
Thumbnails should not get counted ..
-phil.
On 06/01/2016 01:06 AM, Jayathirth D V wrote:
Updated bug title in JBS as it was misleading.
*From:* Jayathirth D V
*Sent:* Wednesday, June 01, 2016 12:48 PM
*To:* Philip Race; Jim Graham
*Cc:* 2d-dev@openjdk.java.net <mailto:2d-dev@openjdk.java.net>
*Subject:* Review Request for JDK-8152672 : Exception getting
thumbnail size for JPEG with embedded thumbnail
Hi,
_Please review the following fix in JDK9:_
Bug : https://bugs.openjdk.java.net/browse/JDK-8152672
Webrev : http://cr.openjdk.java.net/~jdv/8152672/webrev.00/
<http://cr.openjdk.java.net/%7Ejdv/8152672/webrev.00/>
Issue : When we are trying to get properties related to second image
in JPEG file we are getting IIOException mentioning that it is not a
JPEG file.
Root cause : When we are skipping first image to reach second image
header, we are just trying to find next available EOI marker. But if
first image has embedded thumbnail in APP1 marker, we will reach to
EOI of this thumbnail and not EOI of first image. So after we reach
EOI of embedded thumbnail we try to access second image SOI marker
which will fail.
Solution : We have to change the logic of how we skip to consecutive
images in JPEG file. We know that application markers, comments or
other markers can contain data same as SOI & EOI. Instead of just
checking for EOI marker serially, we should read length of these
markers and skip them.
Thanks,
Jay
