iproute2: Fail "ip netns add" on existing network namespaces.

Use O_EXCL so that we only create and mount a new network namespace
if there is no chance an existing network namespace is present.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index dff3497aa598d6740ec3199eaba77201c8e1e3d5..e41a598a847fb24049e6d1a63a746be221816abe 100644 (file)
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -41,16 +41,6 @@ static int setns(int fd, int nstype)
 #endif /* HAVE_SETNS */
 
 
-static int touch(const char *path, mode_t mode)
-{
-       int fd;
-       fd = open(path, O_RDONLY|O_CREAT, mode);
-       if (fd < 0)
-               return -1;
-       close(fd);
-       return 0;
-}
-
 static void usage(void) __attribute__((noreturn));
 
 static void usage(void)
@@ -214,6 +204,7 @@ static int netns_add(int argc, char **argv)
         */
        char netns_path[MAXPATHLEN];
        const char *name;
+       int fd;
 
        if (argc < 1) {
                fprintf(stderr, "No netns name specified\n");
@@ -227,11 +218,13 @@ static int netns_add(int argc, char **argv)
        mkdir(NETNS_RUN_DIR, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH);
 
        /* Create the filesystem state */
-       if (touch(netns_path, 0) < 0) {
+       fd = open(netns_path, O_RDONLY|O_CREAT|O_EXCL, 0);
+       if (fd < 0) {
                fprintf(stderr, "Could not create %s: %s\n",
                        netns_path, strerror(errno));
-               goto out_delete;
+               return -1;
        }
+       close(fd);
        if (unshare(CLONE_NEWNET) < 0) {
                fprintf(stderr, "Failed to create a new network namespace: %s\n",
                        strerror(errno));