Package: release.debian.org
Severity: normal
User: release.debian....@packages.debian.org
Usertags: unblock
Dear release masters,
I would like to ask for unblocking
texlive-bin 2016.20160513.41080.dfsg-2
The package fixes a long reported problem: #796490
that made reproducible builds failed when png images
with alpha channels were included into PDF documents
using pdftex.
The reason for this is an allocation of memory double
the size of the actual png, and thus the second half
as embedded into the PDF document contains memory noise.
This can in fact be a security concern (diffusion of
information).
The fix was found by David Fifield, reported to the pdftex
mailing list, and is already included in the TeX Live
sources (svn 43637).
Following are the explanations of David, which are also
available in the quilt patch:
/*********************
I think I found the cause of this bug. It's a bug in pdfTeX that results
in uninitialized memory being copied to the output file. I have reported
the bug upstream:
https://www.tug.org/pipermail/pdftex/2017-March/009100.html
The function write_png_rgb_alpha allocates twice as much memory as is
necessary for the smask buffer. The second half of the buffer is left
uninitialized and the whole buffer is copied to the output PDF file. It
only arises with PNG images that have an alpha channel. (I suppose
optipng removes the alpha channel when possible, which is why it made
the problem go away.)
I think the bug is in texk/web2c/pdftexdir/writepng.c, where a "/ 2"
should be "/ 4"; i.e., 1 in 4 bytes is an alpha byte:
smask_size = (png_get_rowbytes(png_ptr(img), png_info(img)) / 2)
* png_get_image_height(png_ptr(img), png_info(img));
Interestingly, texk/web2c/luatexdir/image/writepng.w gets it right:
smask_size = (int) ((png_get_rowbytes(png_p, info_p) / 4) *
png_get_image_height(png_p, info_p));
Reproduction instructions:
1. (optional) Install texlive-binaries-dbgsym (for line numbers in
valgrind output).
sudo sh -c 'echo "deb http://debug.mirrors.debian.org/debian-debug/
stretch-debug main" > /etc/apt/sources.list.d/debian-debug.list'
sudo apt-get update
sudo apt-get install texlive-binaries-dbgsym
2. Run valgrind and see errors.
valgrind pdflatex ownCloudClientManual.tex
Note that the valgrind stack trace says write_png_gray_alpha, not
write_png_rgb_alpha, probably as an artifact of optimization.
==13526== Conditional jump or move depends on uninitialised value(s)
==13526== at 0x4C300D3: memcpy@GLIBC_2.2.5 (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==13526== by 0x506E425: ??? (in /lib/x86_64-linux-gnu/libz.so.1.2.8)
==13526== by 0x506EE67: ??? (in /lib/x86_64-linux-gnu/libz.so.1.2.8)
==13526== by 0x506FE53: deflate (in /lib/x86_64-linux-gnu/libz.so.1.2.8)
==13526== by 0x199F99: writezip (writezip.c:71)
==13526== by 0x15215C: pdfflush.part.39 (pdftex0.c:18943)
==13526== by 0x18FA1D: write_png_rgb_alpha (writepng.c:381)
==13526== by 0x18FA1D: write_png (writepng.c:662)
==13526== by 0x18A836: writeimage (writeimg.c:370)
==13526== by 0x16BB78: zpdfwriteimage (pdftex0.c:22285)
==13526== by 0x16D794: zpdfshipout (pdftex0.c:24722)
==13526== by 0x17F65C: maincontrol (pdftex0.c:38501)
==13526== by 0x12F5B9: mainbody (pdftexini.c:5656)
==13526==
==13526== Conditional jump or move depends on uninitialised value(s)
==13526== at 0x4C301EB: memcpy@GLIBC_2.2.5 (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==13526== by 0x506E425: ??? (in /lib/x86_64-linux-gnu/libz.so.1.2.8)
==13526== by 0x506EE67: ??? (in /lib/x86_64-linux-gnu/libz.so.1.2.8)
==13526== by 0x506FE53: deflate (in /lib/x86_64-linux-gnu/libz.so.1.2.8)
==13526== by 0x199F99: writezip (writezip.c:71)
==13526== by 0x15215C: pdfflush.part.39 (pdftex0.c:18943)
==13526== by 0x18FA1D: write_png_rgb_alpha (writepng.c:381)
==13526== by 0x18FA1D: write_png (writepng.c:662)
==13526== by 0x18A836: writeimage (writeimg.c:370)
==13526== by 0x16BB78: zpdfwriteimage (pdftex0.c:22285)
==13526== by 0x16D794: zpdfshipout (pdftex0.c:24722)
==13526== by 0x17F65C: maincontrol (pdftex0.c:38501)
==13526== by 0x12F5B9: mainbody (pdftexini.c:5656)
.. more ..
\*********************************************
The debdiff contains only his the following items:
debian/changelog:
@@ -1,3 +1,12 @@
+texlive-bin (2016.20160513.41080.dfsg-2) unstable; urgency=medium
+
+ * cherrypick upstream svn43637 (Closes: #796490)
+ When embedding png images with alpha channel, pdftex did embed
+ twice as much memory and left the second half uninitialized.
+ Thanks to David Fifield for research and fix.
+
+ -- Norbert Preining <prein...@debian.org> Thu, 30 Mar 2017 10:02:29 +0900
+
debian/patches/series:
@@ -44,3 +44,4 @@
#update-mplibdir-luatex1
#update-luatexdir-luatex1
teckit-dont-build-sfconv
+upstream-svn43637-pdftex-dont-embed-unitialized-memory-png-alpha
And the actual patch
upstream-svn43637-pdftex-dont-embed-unitialized-memory-png-alpha
where I quote only the code part, the rest is the explanation of
David I copied into the quilt patch:
---
texk/web2c/pdftexdir/ChangeLog | 6 ++++++
texk/web2c/pdftexdir/writepng.c | 2 +-
2 files changed, 7 insertions(+), 1 deletion(-)
--- texlive-bin.orig/texk/web2c/pdftexdir/ChangeLog
+++ texlive-bin/texk/web2c/pdftexdir/ChangeLog
@@ -1,3 +1,9 @@
+2017-03-29 Akira Kakuto <kak...@fuk.kindai.ac.jp>
+
+ * writepng.c: Fix the size of memory to allocate when writing
+ SMask in write_png_rgb_alpha. Reported by David Fifield:
+ http://tug.org/pipermail/pdftex/2017-March/009100.html.
+
2016-07-16 Akira Kakuto <kak...@fuk.kindai.ac.jp>
* pdftoepdf.cc: Use zround(stemV->getNum()) instead of stemV->getInt()
--- texlive-bin.orig/texk/web2c/pdftexdir/writepng.c
+++ texlive-bin/texk/web2c/pdftexdir/writepng.c
@@ -335,7 +335,7 @@
pdfcreateobj(0, 0);
smask_objnum = objptr;
pdf_printf("/SMask %i 0 R\n", (int) smask_objnum);
- smask_size = (png_get_rowbytes(png_ptr(img), png_info(img)) / 2)
+ smask_size = (png_get_rowbytes(png_ptr(img), png_info(img)) / 4)
* png_get_image_height(png_ptr(img), png_info(img));
smask = xtalloc(smask_size, png_byte);
pdfbeginstream();
Thanks for your consideration.
unblock texlive-bin/2016.20160513.41080.dfsg-2
Norbert
-- System Information:
Debian Release: 9.0
APT prefers unstable-debug
APT policy: (500, 'unstable-debug'), (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 4.10.0 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
