Bug 1691636 (CVE-2018-19872)

External References:

https://bugreports.qt.io/browse/QTBUG-69449
https://wiki.qt.io/Qt_5.11.3_Change_Files

Created qt tracking bugs for this issue:

Affects: fedora-all [bug 1691638]


Created qt5 tracking bugs for this issue:

Affects: fedora-all [bug 1691637]

You can list all versions of qt3 as not affected. I verified that this code is not present in Qt 3, it was introduced in Qt 4.0.0.

qt-4.8.7-45.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.

I don't see how you can come to the conclusion that rhel-*/qt=notaffected. I have seen the vulnerable code in ALL versions of Qt 4, from 4.0.0 to 4.8.7.

Backtrace from 5.11.1:

```
Program received signal SIGFPE, Arithmetic exception.
0x00007ffff7a741ca in scale_pbm_color (bv=12336, gv=12336, rv=12336, mx=0)
    at ../../include/QtGui/../../src/gui/painting/qrgba64.h:79
79	../../include/QtGui/../../src/gui/painting/qrgba64.h: No such file or directory.
(gdb) bt
#0  0x00007ffff7a741ca in scale_pbm_color (bv=12336, gv=12336, rv=12336, mx=0)
    at ../../include/QtGui/../../src/gui/painting/qrgba64.h:79
#1  read_pbm_body (outImage=0x7fffffffd490, mcc=1329790976, h=3, w=<optimized out>, 
    type=<optimized out>, device=0x61c330) at image/qppmhandler.cpp:193
#2  QPpmHandler::read (this=0x61c8b0, image=0x7fffffffd490) at image/qppmhandler.cpp:509
#3  0x00007ffff7a46a8a in QImageReader::read (this=0x7fffffffd4e8, image=0x7fffffffd490)
    at image/qimagereader.cpp:1313
#4  0x00007ffff7a470d8 in QImageReader::read (this=this@entry=0x7fffffffd4e8)
    at image/qimagereader.cpp:1261
#5  0x00007ffff7a2f0da in QImage::load (this=0x7fffffffd560, fileName=..., format=<optimized out>)
    at image/qimage.cpp:3460
#6  0x0000000000400ce2 in main (argc=2, argv=0x7fffffffd6d8) at main.cpp:14
(gdb) 
```

Unable to reproduce this on Red Hat Enterprise 6 or 7 (7 running qt 4.8.7).

```
static inline QRgb scale_pbm_color(quint16 mx, quint16 rv, quint16 gv, quint16 bv)
{
    return QRgba64::fromRgba64((rv * 0xffffu) / mx, (gv * 0xffffu) / mx, (bv * 0xffffu) / mx, 0xffff).toArgb32();
}
```

Looks like MX is 0 and a nice exception occurs.

Unrelated, but interesting. Division by zero is undefined behavior. gcc seems to generate a SIGFPE, whereas clang/llvm seems to generate junk and continue. Easiest way to detect this via a clang build is with -fsanitize=undefined. I'm sure there are a bunch of other knobs and switches to change the behavior.

Red Hat Enterprise Linux 7 looks like it has the responsible code even though I couldn't reproduce it.. Didn't track down where/why mx is getting set to zero, but 7 could potentially be impacted. The code doesn't appear in earlier versions to the best of my knowledge.

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2020:1172 https://access.redhat.com/errata/RHSA-2020:1172

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2018-19872

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2020:1665 https://access.redhat.com/errata/RHSA-2020:1665