Merge "Merge remote-tracking branch 'origin/5.5' into 5.6" into refs/staging/5.6

1 files changed, 25 insertions, 21 deletions

diff --git a/src/corelib/io/qfsfileengine.cpp b/src/corelib/io/qfsfileengine.cpp
index 429c40da1a..10e116a23a 100644
--- a/src/corelib/io/qfsfileengine.cpp
+++ b/src/corelib/io/qfsfileengine.cpp
@@ -724,29 +724,33 @@ qint64 QFSFileEnginePrivate::writeFdFh(const char *data, qint64 len)
 
     qint64 writtenBytes = 0;
 
-    if (fh) {
-        // Buffered stdlib mode.
-
-        size_t result;
-        do {
-            result = fwrite(data + writtenBytes, 1, size_t(len - writtenBytes), fh);
-            writtenBytes += result;
-        } while (result == 0 ? errno == EINTR : writtenBytes < len);
+    if (len) { // avoid passing nullptr to fwrite() or QT_WRITE() (UB)
 
-    } else if (fd != -1) {
-        // Unbuffered stdio mode.
+        if (fh) {
+            // Buffered stdlib mode.
+
+            size_t result;
+            do {
+                result = fwrite(data + writtenBytes, 1, size_t(len - writtenBytes), fh);
+                writtenBytes += result;
+            } while (result == 0 ? errno == EINTR : writtenBytes < len);
+
+        } else if (fd != -1) {
+            // Unbuffered stdio mode.
+
+            SignedIOType result;
+            do {
+                // calculate the chunk size
+                // on Windows or 32-bit no-largefile Unix, we'll need to read in chunks
+                // we limit to the size of the signed type, otherwise we could get a negative number as a result
+                quint64 wantedBytes = quint64(len) - quint64(writtenBytes);
+                UnsignedIOType chunkSize = std::numeric_limits<SignedIOType>::max();
+                if (chunkSize > wantedBytes)
+                    chunkSize = wantedBytes;
+                result = QT_WRITE(fd, data + writtenBytes, chunkSize);
+            } while (result > 0 && (writtenBytes += result) < len);
+        }
 
-        SignedIOType result;
-        do {
-            // calculate the chunk size
-            // on Windows or 32-bit no-largefile Unix, we'll need to read in chunks
-            // we limit to the size of the signed type, otherwise we could get a negative number as a result
-            quint64 wantedBytes = quint64(len) - quint64(writtenBytes);
-            UnsignedIOType chunkSize = std::numeric_limits<SignedIOType>::max();
-            if (chunkSize > wantedBytes)
-                chunkSize = wantedBytes;
-            result = QT_WRITE(fd, data + writtenBytes, chunkSize);
-        } while (result > 0 && (writtenBytes += result) < len);
     }
 
     if (len &&  writtenBytes == 0) {