iproute2: Make "ip netns delete" more likely to succeed

Sometimes "ip netns delete" fails because it can not delete the file a
network namespace was mounted on.  If this only happened when a
network namespace was really in use this would be fine, but today it
is possible to pin all network namespaces by simply having a long
running process started with "ip netns exec".

Every mount is copied when a network namespace is created so it is
impossible to prevent the mounts from getting into other mount
namespaces.  Modify all mounts in the files and subdirectories of
/var/run/netns to be shared mount points so that unmount events can
propogate, making it unlikely that "ip netns delete" will fail because
a directory is mounted in another mount namespace.

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

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 4fce379a4b2e307be9d254c853ba09d4d48f2da6..33765b588a1a3c7fe5baaeb7e2fa222c48d96d49 100644 (file)
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -208,6 +208,7 @@ static int netns_add(int argc, char **argv)
        char netns_path[MAXPATHLEN];
        const char *name;
        int fd;
+       int made_netns_run_dir_mount = 0;
 
        if (argc < 1) {
                fprintf(stderr, "No netns name specified\n");
@@ -220,6 +221,29 @@ static int netns_add(int argc, char **argv)
        /* Create the base netns directory if it doesn't exist */
        mkdir(NETNS_RUN_DIR, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH);
 
+       /* Make it possible for network namespace mounts to propogate between
+        * mount namespaces.  This makes it likely that a unmounting a network
+        * namespace file in one namespace will unmount the network namespace
+        * file in all namespaces allowing the network namespace to be freed
+        * sooner.
+        */
+       while (mount("", NETNS_RUN_DIR, "none", MS_SHARED | MS_REC, NULL)) {
+               /* Fail unless we need to make the mount point */
+               if (errno != EINVAL || made_netns_run_dir_mount) {
+                       fprintf(stderr, "mount --make-shared %s failed: %s\n",
+                               NETNS_RUN_DIR, strerror(errno));
+                       return EXIT_FAILURE;
+               }
+
+               /* Upgrade NETNS_RUN_DIR to a mount point */
+               if (mount(NETNS_RUN_DIR, NETNS_RUN_DIR, "none", MS_BIND, NULL)) {
+                       fprintf(stderr, "mount --bind %s %s failed: %s\n",
+                               NETNS_RUN_DIR, NETNS_RUN_DIR, strerror(errno));
+                       return EXIT_FAILURE;
+               }
+               made_netns_run_dir_mount = 1;
+       }
+
        /* Create the filesystem state */
        fd = open(netns_path, O_RDONLY|O_CREAT|O_EXCL, 0);
        if (fd < 0) {