nxm: drain socket lines before emitting to dodge use-after-free

processSocketData iterated socket->canReadLine() and emit'd nxmReceived
inside the loop. nxmReceived routes to OrganizerCore which can show a
modal dialog (the "Wrong Game" warning fires whenever the link's game
domain doesn't match the active instance). Modal dialogs spin the event
loop, and the loop processes the disconnected → deleteLater queued for
the same socket. The socket gets freed, then control returns to the
while loop and the next canReadLine() runs on a dangling pointer.

Repro hits cleanly when an nxm:// for a non-matching game arrives — the
"Wrong Game" dialog appears and as soon as the user dismisses it MO2
crashes with SIGSEGV. Read into a QStringList first, then emit after
the read loop ends so the socket is no longer touched once handlers run.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/src/src/nxmhandler_linux.cpp b/src/src/nxmhandler_linux.cpp
index c7db527..7b70ff4 100644
--- a/src/src/nxmhandler_linux.cpp
+++ b/src/src/nxmhandler_linux.cpp
@@ -301,12 +301,20 @@ void NxmHandlerLinux::onNewConnection()
 
 void NxmHandlerLinux::processSocketData(QLocalSocket* socket)
 {
+  // Drain all available lines before emitting anything. Slot handlers for
+  // nxmReceived/directDownloadReceived can show modal dialogs (e.g. the
+  // "Wrong Game" warning) that spin the event loop. That re-entry would
+  // process the disconnected → deleteLater queued for this socket and free
+  // it, leaving the canReadLine() loop iterating on a dangling pointer.
+  QStringList lines;
   while (socket->canReadLine()) {
     const QString line = QString::fromUtf8(socket->readLine()).trimmed();
-    if (line.isEmpty()) {
-      continue;
+    if (!line.isEmpty()) {
+      lines.append(line);
     }
+  }
 
+  for (const QString& line : lines) {
     log::info("received link on socket: {}", line);
 
     // Try NXM-style parse first (nxm:// or modl:// with /mods/ID/files/ID path).