process: Avoid late failure if /dev/null cannot be opened.

It is (very slightly) risky to open /dev/null every time that we need it,
because open can fail.  So this commit opens /dev/null in advance instead.

Coverity #10719.

diff --git a/lib/process.c b/lib/process.c
index 6e9ea8e..8263437 100644 (file)
--- a/lib/process.c
+++ b/lib/process.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -195,6 +195,7 @@ process_start(char **argv,
               struct process **pp)
 {
     sigset_t oldsigs;
+    int nullfd;
     pid_t pid;
     int error;
 
@@ -205,6 +206,15 @@ process_start(char **argv,
         return error;
     }
 
+    if (n_null_fds) {
+        nullfd = get_null_fd();
+        if (nullfd < 0) {
+            return -nullfd;
+        }
+    } else {
+        nullfd = -1;
+    }
+
     block_sigchld(&oldsigs);
     pid = fork();
     if (pid < 0) {
@@ -225,15 +235,17 @@ process_start(char **argv,
         unblock_sigchld(&oldsigs);
         for (fd = 0; fd < fd_max; fd++) {
             if (is_member(fd, null_fds, n_null_fds)) {
-                /* We can't use get_null_fd() here because we might have
-                 * already closed its fd. */
-                int nullfd = open("/dev/null", O_RDWR);
                 dup2(nullfd, fd);
-                close(nullfd);
-            } else if (fd >= 3 && !is_member(fd, keep_fds, n_keep_fds)) {
+            } else if (fd >= 3 && fd != nullfd
+                       && !is_member(fd, keep_fds, n_keep_fds)) {
                 close(fd);
             }
         }
+        if (nullfd >= 0
+            && !is_member(nullfd, keep_fds, n_keep_fds)
+            && !is_member(nullfd, null_fds, n_null_fds)) {
+            close(nullfd);
+        }
         execvp(argv[0], argv);
         fprintf(stderr, "execvp(\"%s\") failed: %s\n",
                 argv[0], strerror(errno));