QFSFileEngine: fix overflow bug when using lseek64

QT_LSEEK (lseek64()) returns QT_OFF_T, which is off64_t on 32bit
systems. The return from the lseek64() call was being assigned to an
int, which meant that if the returned value is > INT_MAX it will
overflow and the value becomes -1, and since errno would be EOVERFLOW
the code would fail to open the file.

Fix the issue by assigning the return value to QT_OFF_T.

Thanks to Giuseppe for pointing out the issue in the code review.

Found by compiling with -Wshorten-64-to-32.

[ChangeLog][QtCore][QFile] Fixed a bug where opening a file in append
mode may fail if the file size was bigger than INT_MAX.

Pick-to: 6.5 6.4 6.2 5.15
Change-Id: Iad33e3192f37466643a1218d38e5ecc2baaa7dc9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/corelib/io/qfsfileengine.cpp b/src/corelib/io/qfsfileengine.cpp
index d924b22431..ffc4878e0d 100644
--- a/src/corelib/io/qfsfileengine.cpp
+++ b/src/corelib/io/qfsfileengine.cpp
@@ -328,7 +328,7 @@ bool QFSFileEnginePrivate::openFd(QIODevice::OpenMode openMode, int fd)
 
     // Seek to the end when in Append mode.
     if (openMode & QFile::Append) {
-        int ret;
+        QT_OFF_T ret;
         do {
             ret = QT_LSEEK(fd, 0, SEEK_END);
         } while (ret == -1 && errno == EINTR);