[Python-modules-team] Bug#935909: python3-pyqt5: Segmentation fault when switching between image and text with html tags using style sheets

[Danny Milosavljevic]

Package: python3-pyqt5
Version: 5.11.3+dfsg-1+b3
Severity: important

Dear Maintainer,

there is a segmentation fault problem with python3-qt5 and/or qt5 when switching between image and text with html tags.

To reproduce,

(1) Use Debian 10 live iso (or any Debian 10; it happened on a finished installation as well)
(2) Invoke: sudo apt-get update
(3) Invoke: sudo apt-get install python3-pyqt5
(4) Invoke: cp /usr/share/icons/Adwaita/48x48/status/network-wired-disconnected.png .
(or any other png)
(5) Save the text below as "a.py"
(6) Invoke: QT_QPA_PLATFORM=offscreen python3 a.py 1
(7) Wait for 5 seconds
(8) See the segmentation fault

It's very very reproducible for me.

Text:

from PyQt5.QtWidgets import QWidget, QLabel, QApplication
from PyQt5.QtCore import QTimer, QVariant, pyqtSlot


style=\
"""QLabel {
    qproperty-alignment: AlignCenter;
    min-width: 84px;
    min-height: 84px; 
    max-width: 84px;
    max-height: 84px; 
    }
QLabel[state="image"]{
    background-image: url(network-wired-disconnected.png);
    background-repeat: no-repeat;
    background-position: center;
    background-color: #eeeeee;
    qproperty-text: " ";
}
QLabel[state="text"]{
    background-image: none;
    background-repeat: no-repeat;
    background-position: center;
    background-color: #eeeeee;
    qproperty-text: "This is<br>an<br>example";
    } 
"""
style2=\
"""QLabel {
    qproperty-alignment: AlignCenter;
    min-width: 84px;
    min-height: 84px; 
    max-width: 84px;
    max-height: 84px; 
    }
QLabel[state="image"]{
    background-color: orange;
    qproperty-text: "Image";
}
QLabel[state="text"]{
    background-color: #eeeeee;
    qproperty-text: "This is<br>an<br>example";
    } 
"""
# NO segfault!!
style3=\
"""QLabel {
    qproperty-alignment: AlignCenter;
    min-width: 84px;
    min-height: 84px; 
    max-width: 84px;
    max-height: 84px; 
    }
QLabel[state="image"]{
    background-color: orange;
    qproperty-text: "Image";
}
QLabel[state="text"]{
    background-color: #eeeeee;
    qproperty-text: "Text";
    } 
"""
style4=\
"""QLabel {
    qproperty-alignment: AlignCenter;
    border: 1px solid #cccccc;
    border-bottom: 1px solid white;
    background-color: #eeeeee;
    padding: 2px;
    font-size: 15px;
    font-family: "free sans";
    qproperty-alignment: AlignCenter;
    min-width: 84px;
    min-height: 84px; 
    max-width: 84px;
    max-height: 84px; 
    }
QLabel[state="image"]{
    background-color: orange;
    qproperty-text: "Image";
}
QLabel[state="text"]{
    background-color: #eeeeee;
    qproperty-text: "<table><tr><td>This is a</td></tr><tr><td>Text</td></tr></table>";
    } 
"""
# NO segfault!!
style5=\
"""QLabel {
    qproperty-alignment: AlignCenter;
    min-width: 84px;
    min-height: 84px; 
    max-width: 84px;
    max-height: 84px; 
    }
QLabel[state="image"]{
    background-image: url(network-wired-disconnected.png);
    background-repeat: no-repeat;
    background-position: center;
    background-color: #eeeeee;
    qproperty-text: " ";
}
QLabel[state="text"]{
    background-image: none;
    background-repeat: no-repeat;
    background-position: center;
    background-color: #eeeeee;
    qproperty-text: "Text";
    }
"""
# Program crashes with "segmentation fault" when
# html-tags are in the label text
# -----------------------------------
# -----------------------------------
class LabelDemoWidget(QWidget):
    def __init__(self, style=style, parent=None):
        QWidget.__init__(self, parent=parent)
        
        self.style=style
        self.topLabel=QLabel(self)
        self.topLabel.setObjectName("topLabel")
        self.label_prop="text"
        self.switch={"text":"image","image":"text"}
        self.setGeometry(100, 100, 100, 100)
        flip=QTimer(self)
        flip.setInterval(1000)
        flip.timeout.connect(self.new_style)
        flip.start()
# -----------------------------------
    @pyqtSlot()
    def new_style(self):
        self.topLabel.setProperty("state",QVariant(self.switch[self.label_prop]))
        self.label_prop=self.switch[self.label_prop]
        self.setStyleSheet(self.style)
# -----------------------------------
if __name__=='__main__':
    # usage python3 label_demo.py 0 ... 4
    # 2 and 4 cause no segfault
    # all others with html-tags in text will crash after some time with segfault
    # debian buster (10) with python3 (3.7.3), python3-qt5 (5.11.3) out of the box
    
    import sys
    app=QApplication(sys.argv)
    w = LabelDemoWidget([style, style2, style3, style4, style5][int(sys.argv[1])])
    w.show()
    sys.exit(app.exec_())

-- System Information:
Debian Release: 10.0
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-5-amd64 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages python3-pyqt5 depends on:
ii  libc6                             2.28-10
ii  libgcc1                           1:8.3.0-6
ii  libpython3.7                      3.7.3-2
ii  libqt5core5a [qtbase-abi-5-11-3]  5.11.3+dfsg1-1
ii  libqt5dbus5                       5.11.3+dfsg1-1
ii  libqt5designer5                   5.11.3-4
ii  libqt5gui5                        5.11.3+dfsg1-1
ii  libqt5help5                       5.11.3-4
ii  libqt5network5                    5.11.3+dfsg1-1
ii  libqt5printsupport5               5.11.3+dfsg1-1
ii  libqt5test5                       5.11.3+dfsg1-1
ii  libqt5widgets5                    5.11.3+dfsg1-1
ii  libqt5xml5                        5.11.3+dfsg1-1
ii  libstdc++6                        8.3.0-6
ii  python3                           3.7.3-1
ii  python3-sip [sip-py3api-12.5]     4.19.14+dfsg-2

python3-pyqt5 recommends no packages.

Versions of packages python3-pyqt5 suggests:
pn  python3-pyqt5-dbg  <none>

-- no debconf information