nlt_type3[i] not initialized when get_nonlinear_transform() == false

[MrApplejuice]

Dear library maintainers. I found this bug while working on my work-project, but I do not have any knowledge of how jpeg2000 compression works internally, so this is a "contextual fix". Here my observations and analysis:

Symptoms

I am working with images stored on AWS HealthImaging. AWS is transcoding medical data to jpeg2000 compressed images. AWS also computes CRC32 checksums on the decompressed image data. While working on a data-loader, I noticed that CRC32 sums randomly did not match.

I turned to valgrind and analyzed my loader and traced the issue to the line

OpenJPH/src/core/codestream/ojph_tile.cpp

Line 421 in a0ae0ee

if (is_signed[comp_num] && nlt_type3[comp_num] == type3)

for which valgrind reported that this "conditional jump depends on unitialized data".

Analysis

By adding some more if-statements, I found out that the uninitialized data meant was nlt_type3[comp_num]. This seems to get initialized in this code section:

OpenJPH/src/core/codestream/ojph_tile.cpp

Lines 270 to 280 in a0ae0ee

	num_bits[i] = szp->get_bit_depth(i);
	is_signed[i] = szp->is_signed(i);
	bool result = nlp->get_nonlinear_transform(i, bd, is, nlt_type3[i]);
	if (result == true && (bd != num_bits[i] || is != is_signed[i]))
	OJPH_ERROR(0x000300A1, "Mismatch between Ssiz (bit_depth = %d, "
	"is_signed = %s) from SIZ marker segment, and BDnlt "
	"(bit_depth = %d, is_signed = %s) from NLT marker segment, "
	"for component %d", i, num_bits[i],
	is_signed[i] ? "True" : "False", bd, is ? "True" : "False");
	cur_line[i] = 0;
	reversible[i] = codestream->get_coc(i)->is_reversible();

From what I could derive, jpeg2000 images can use the "non linear transform" optionally, but if it is not used, nlp->get_nonlinear_transform(i, bd, is, nlt_type3[i]) returns false, and nlt_type3[i] is never set. I quickly checked the param_nlt::nonlinearity type and saw that it seems to define the value OJPH_NLT_NO_NLT which seems to match this case.

Proposed solution

Set nlt_type3[i] = param_nlt::nonlinearity::OJPH_NLT_NO_NLT; when nonlinear-transform is disabled.

I have no idea if this is "correct" but it seems to fix the issue. With the fix, I now can reliably decode images from AWS HealthImaging with no hickups and valgrind is also happy.

[aous72]

Hi Paul,

Thank you for this extensive and very clear bug report, and for PR.

I totally agree.

Kind regards,
Aous.

[MrApplejuice]

Thank you for this extensive and very clear bug report, and for PR.

Really no problem! Thanks to you for maintaining this library and already making a hotfix release for the fix - that is very handy for me!

[aous72]

Thank you.
Just to let you know that I forgot to update the internal version when I release version 0.24.2: see #221. This has been corrected now.