https://bugs.kde.org/show_bug.cgi?id=400610
Bug ID: 400610
Summary: Application crashes with SIGBUS if XDG_CACHE_HOME is
too small (or maybe out of space)
Product: frameworks-kcoreaddons
Version: unspecified
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Qt application crashes with SIGBUS if XDG_CACHE_HOME is too small
We were able to track down the problem to:
- Package: kde-frameworks/kcoreaddons-5.51.0
- File: src/lib/caching/kshareddatacache.cpp
- Function: void mapSharedMemory()
- Lines: 1051 - 1053
- Code:
if (file.open(QIODevice::ReadWrite) &&
(file.size() >= size ||
(file.resize(size) && ensureFileAllocated(file.handle(), size)))) {
STEPS TO REPRODUCE
1) Create a small filesystem (as root): mount -t tmpfs -o size=30k tmpfs /mnt
The size seems to depend on the system. If the value in '-o size=' is too small
or too high, you won't get a SIGBUS crash. 30k works on my machine.
2) Create a small test program (as suggested by user "mv")
File a.cc:
#include <QApplication>
#include <qframe.h>
int main(int argc, char ** argv) {
QApplication a(argc,argv);
QFrame *view = new QFrame();
view->show();
a.connect(&a,SIGNAL(lastWindowClosed()),&a,SLOT(quit()));
return a.exec();
}
File: a.pro
TARGET = a
SOURCES = a.cc
QT += widgets
3) Compile the program and run it:
qmake && make
XDG_CACHE_HOME=/mnt ./a
4) The program will crash with SIGBUS
5) You can get more details using strace:
XDG_CACHE_HOME=/mnt strace -o /tmp/strace-log -f ./a
6) strace-log shows:
1500 openat(AT_FDCWD, "/mnt/icon-cache.kcache", O_RDWR|O_CREAT|O_CLOEXEC,
0666) = 9
1500 statx(9, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL,
{stx_mask=STATX_BASIC_STATS, stx_attributes=0, stx_mode=S_IFREG|0640,
stx_size=0, ...}) = 0
1500 lseek(9, 0, SEEK_CUR) = 0
1500 ftruncate(9, 10547304) = 0
1500 fallocate(9, 0, 0, 10547304) = -1 ENOSPC (No space left on device)
1500 mmap(NULL, 10547304, PROT_READ|PROT_WRITE, MAP_SHARED, 9, 0) =
0x7f71484df000
1500 --- SIGBUS {si_signo=SIGBUS, si_code=BUS_ADRERR,
si_addr=0x7f71484e3020} ---
The mmap should have stopped with an error message after fallocate, since this
function failed. But the error was ignored and the program continued with an
mmap. A subsequent memory access to the mmaped memory failed with SIGBUS.
7) The lines in the strace log correspond to lines 1051 - 1053 of
src/lib/caching/kshareddatacache.cpp
OBSERVED RESULT: SIGBUS
EXPECTED RESULT: Error message stating that XDG_CACHE_HOME is out of space,
followed by a regular abort() or exit().
SOFTWARE VERSIONS
- OS: Gentoo Linux
- KDE Plasma Version: 5.14.2
- KDE Frameworks Version: 5.51.0
- Qt Version: 5.11.2
ADDITIONAL INFORMATION
- Look at https://forums.gentoo.org/viewtopic-t-1087812.html for additional
information.
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