bubblewrap: Do not leak FDs dedicated to setup_newroot

The options --file, --bind-data and --ro-bind-data take a file
descriptor as first argument. This FD is then used to set up the new
root file system. These FDs are then closed after this step. However,
when the privileged mode is used, this step is run in a child process,
hence leaking the FDs in the parent process.

To avoid future omissions, this patch walk through all the file
descriptors tied to an option and try to close them. To avoid a double
close, it marks FDs closed by setup_newroot as such.

Signed-off-by: Mickaël Salaün <mic@digikod.net>

Closes: #243
Approved by: cgwalters

bubblewrap.c

@@ -1147,6 +1147,7 @@ setup_newroot (bool unshare_pid,
               die_with_error ("Can't write data to file %s", op->dest);
 
             close (op->fd);
+            op->fd = -1;
           }
           break;
 
@@ -1164,6 +1165,7 @@ setup_newroot (bool unshare_pid,
               die_with_error ("Can't write data to file %s", op->dest);
 
             close (op->fd);
+            op->fd = -1;
 
             assert (dest != NULL);
 
@@ -1203,6 +1205,22 @@ setup_newroot (bool unshare_pid,
                  PRIV_SEP_OP_DONE, 0, NULL, NULL);
 }
 
+/* Do not leak file descriptors already used by setup_newroot () */
+static void
+close_ops_fd (void)
+{
+  SetupOp *op;
+
+  for (op = ops; op != NULL; op = op->next)
+    {
+      if (op->fd != -1)
+        {
+          (void) close (op->fd);
+          op->fd = -1;
+        }
+    }
+}
+
 /* We need to resolve relative symlinks in the sandbox before we
    chroot so that absolute symlinks are handled correctly. We also
    need to do this after we've switched to the real uid so that
@@ -2324,6 +2342,8 @@ main (int    argc,
       setup_newroot (opt_unshare_pid, -1);
     }
 
+  close_ops_fd ();
+
   /* The old root better be rprivate or we will send unmount events to the parent namespace */
   if (mount ("oldroot", "oldroot", NULL, MS_REC | MS_PRIVATE, NULL) != 0)
     die_with_error ("Failed to make old root rprivate");