multi: Warn about failing read in multi_process_file_closed()

Handle failure explicitly instead of the implicit
handling by "while (buffer_i < r)".

Backport of 18d1b1fe00 and the relevant
type fix of 5e5ead5ba0

Reported-by: Marc Heuse <marc@srlabs.de>
Github: openvpn-private-issues#101
Change-Id: I950863eeba67b8c006c794245a1a08752cd79fb0
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Antonio Quartulli <antonio@mandelbit.com>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1444
Message-Id: <20251216111544.27133-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg35113.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

src/openvpn/multi.c

@@ -2830,8 +2830,13 @@ void
 multi_process_file_closed(struct multi_context *m, const unsigned int mpp_flags)
 {
     char buffer[INOTIFY_EVENT_BUFFER_SIZE];
-    size_t buffer_i = 0;
-    int r = read(m->top.c2.inotify_fd, buffer, INOTIFY_EVENT_BUFFER_SIZE);
+    ssize_t buffer_i = 0;
+    ssize_t r = read(m->top.c2.inotify_fd, buffer, INOTIFY_EVENT_BUFFER_SIZE);
+    if (r < 0)
+    {
+        msg(M_WARN | M_ERRNO, "MULTI: multi_process_file_closed error");
+        return;
+    }
 
     while (buffer_i < r)
     {