QFileSystemEngine/Unix: use fchmod(2) if the file is open

This protects against the file having been renamed or deleted. We'll
still operate on the open file, regardless the name it may have on the
filesystem.

Change-Id: I1eba2b016de74620bfc8fffd14cca85cfd672e6d
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 32 insertions, 3 deletions

diff --git a/src/corelib/io/qfilesystemengine_p.h b/src/corelib/io/qfilesystemengine_p.h
index de18c997df..196ed8df69 100644
--- a/src/corelib/io/qfilesystemengine_p.h
+++ b/src/corelib/io/qfilesystemengine_p.h
@@ -92,6 +92,8 @@ public:
                              QFileSystemMetaData::MetaDataFlags what);
 #if defined(Q_OS_UNIX)
     static bool fillMetaData(int fd, QFileSystemMetaData &data); // what = PosixStatFlags
+    static bool setPermissions(int fd, QFile::Permissions permissions, QSystemError &error,
+                               QFileSystemMetaData *data = nullptr);
 #endif
 #if defined(Q_OS_WIN)
 
diff --git a/src/corelib/io/qfilesystemengine_unix.cpp b/src/corelib/io/qfilesystemengine_unix.cpp
index 4ffa6b8972..b26ab2c903 100644
--- a/src/corelib/io/qfilesystemengine_unix.cpp
+++ b/src/corelib/io/qfilesystemengine_unix.cpp
@@ -659,8 +659,7 @@ bool QFileSystemEngine::removeFile(const QFileSystemEntry &entry, QSystemError &
 
 }
 
-//static
-bool QFileSystemEngine::setPermissions(const QFileSystemEntry &entry, QFile::Permissions permissions, QSystemError &error, QFileSystemMetaData *data)
+static mode_t toMode_t(QFile::Permissions permissions)
 {
     mode_t mode = 0;
     if (permissions & (QFile::ReadOwner | QFile::ReadUser))
@@ -681,6 +680,13 @@ bool QFileSystemEngine::setPermissions(const QFileSystemEntry &entry, QFile::Per
         mode |= S_IWOTH;
     if (permissions & QFile::ExeOther)
         mode |= S_IXOTH;
+    return mode;
+}
+
+//static
+bool QFileSystemEngine::setPermissions(const QFileSystemEntry &entry, QFile::Permissions permissions, QSystemError &error, QFileSystemMetaData *data)
+{
+    mode_t mode = toMode_t(permissions);
 
     bool success = ::chmod(entry.nativeFilePath().constData(), mode) == 0;
     if (success && data) {
@@ -693,6 +699,22 @@ bool QFileSystemEngine::setPermissions(const QFileSystemEntry &entry, QFile::Per
     return success;
 }
 
+//static
+bool QFileSystemEngine::setPermissions(int fd, QFile::Permissions permissions, QSystemError &error, QFileSystemMetaData *data)
+{
+    mode_t mode = toMode_t(permissions);
+
+    bool success = ::fchmod(fd, mode) == 0;
+    if (success && data) {
+        data->entryFlags &= ~QFileSystemMetaData::Permissions;
+        data->entryFlags |= QFileSystemMetaData::MetaDataFlag(uint(permissions));
+        data->knownFlagsMask |= QFileSystemMetaData::Permissions;
+    }
+    if (!success)
+        error = QSystemError(errno, QSystemError::StandardLibraryError);
+    return success;
+}
+
 QString QFileSystemEngine::homePath()
 {
     QString home = QFile::decodeName(qgetenv("HOME"));
diff --git a/src/corelib/io/qfsfileengine_unix.cpp b/src/corelib/io/qfsfileengine_unix.cpp
index e152b035e2..3f4f593d81 100644
--- a/src/corelib/io/qfsfileengine_unix.cpp
+++ b/src/corelib/io/qfsfileengine_unix.cpp
@@ -654,7 +654,12 @@ bool QFSFileEngine::setPermissions(uint perms)
 {
     Q_D(QFSFileEngine);
     QSystemError error;
-    if (!QFileSystemEngine::setPermissions(d->fileEntry, QFile::Permissions(perms), error, 0)) {
+    bool ok;
+    if (d->fd != -1)
+        ok = QFileSystemEngine::setPermissions(d->fd, QFile::Permissions(perms), error, 0);
+    else
+        ok = QFileSystemEngine::setPermissions(d->fileEntry, QFile::Permissions(perms), error, 0);
+    if (!ok) {
         setError(QFile::PermissionsError, error.toString());
         return false;
     }