[metacity] session: check fcntl return value

[Alberts Muktupāvels <muktupavels src gnome org>]

commit b960be4fcbd0034fa9bc7bf1b9d081201c27cca3
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Wed Oct 21 13:59:45 2020 +0300

    session: check fcntl return value
    
    This function can fail.
    
    CID 1220275.

 src/core/session.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/src/core/session.c b/src/core/session.c
index 3252f0e6..6d7ea57b 100644
--- a/src/core/session.c
+++ b/src/core/session.c
@@ -131,12 +131,17 @@ new_ice_connection (IceConn connection, IcePointer client_data, Bool opening,
       /* Make sure we don't pass on these file descriptors to any
        * exec'ed children
        */
+      int fd;
+      int flags;
       GIOChannel *channel;
 
-      fcntl (IceConnectionNumber (connection), F_SETFD,
-             fcntl (IceConnectionNumber (connection), F_GETFD, 0) | FD_CLOEXEC);
+      fd = IceConnectionNumber (connection);
+      flags = fcntl (fd, F_GETFD);
 
-      channel = g_io_channel_unix_new (IceConnectionNumber (connection));
+      if (flags == -1 || fcntl (fd, F_SETFD, flags | FD_CLOEXEC) == -1)
+        g_warning ("Failed to set FD_CLOEXEC flag: %s", strerror (errno));
+
+      channel = g_io_channel_unix_new (fd);
 
       input_id = g_io_add_watch (channel,
                                  G_IO_IN | G_IO_ERR,