nfsd: add a usermodehelper upcall for NFSv4 client ID tracking

Add a new client tracker upcall type that uses call_usermodehelper to
call out to a program. This seems to be the preferred method of
calling out to usermode these days for seldom-called upcalls. It's
simple and doesn't require a running daemon, so it should "just work"
as long as the binary is installed.

The client tracking exit operation is also changed to check for a
NULL pointer before running. The UMH upcall doesn't need to do anything
at module teardown time.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 133 insertions, 1 deletions

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 151921bd164e..2fc2f6cb8d95 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -927,6 +927,137 @@ static struct nfsd4_client_tracking_ops nfsd4_cld_tracking_ops = {
         .grace_done     = nfsd4_cld_grace_done,
 };
 
+/* upcall via usermodehelper */
+static char cltrack_prog[PATH_MAX] = "/sbin/nfsdcltrack";
+module_param_string(cltrack_prog, cltrack_prog, sizeof(cltrack_prog),
+                        S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(cltrack_prog, "Path to the nfsdcltrack upcall program");
+
+static int
+nfsd4_umh_cltrack_upcall(char *cmd, char *arg)
+{
+        char *envp[] = { NULL };
+        char *argv[4];
+        int ret;
+
+        if (unlikely(!cltrack_prog[0])) {
+                dprintk("%s: cltrack_prog is disabled\n", __func__);
+                return -EACCES;
+        }
+
+        dprintk("%s: cmd: %s\n", __func__, cmd);
+        dprintk("%s: arg: %s\n", __func__, arg ? arg : "(null)");
+
+        argv[0] = (char *)cltrack_prog;
+        argv[1] = cmd;
+        argv[2] = arg;
+        argv[3] = NULL;
+
+        ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
+        /*
+         * Disable the upcall mechanism if we're getting an ENOENT or EACCES
+         * error. The admin can re-enable it on the fly by using sysfs
+         * once the problem has been fixed.
+         */
+        if (ret == -ENOENT || ret == -EACCES) {
+                dprintk("NFSD: %s was not found or isn't executable (%d). "
+                        "Setting cltrack_prog to blank string!",
+                        cltrack_prog, ret);
+                cltrack_prog[0] = '\0';
+        }
+        dprintk("%s: %s return value: %d\n", __func__, cltrack_prog, ret);
+
+        return ret;
+}
+
+static char *
+bin_to_hex_dup(const unsigned char *src, int srclen)
+{
+        int i;
+        char *buf, *hex;
+
+        /* +1 for terminating NULL */
+        buf = kmalloc((srclen * 2) + 1, GFP_KERNEL);
+        if (!buf)
+                return buf;
+
+        hex = buf;
+        for (i = 0; i < srclen; i++) {
+                sprintf(hex, "%2.2x", *src++);
+                hex += 2;
+        }
+        return buf;
+}
+
+static int
+nfsd4_umh_cltrack_init(struct net __attribute__((unused)) *net)
+{
+        return nfsd4_umh_cltrack_upcall("init", NULL);
+}
+
+static void
+nfsd4_umh_cltrack_create(struct nfs4_client *clp)
+{
+        char *hexid;
+
+        hexid = bin_to_hex_dup(clp->cl_name.data, clp->cl_name.len);
+        if (!hexid) {
+                dprintk("%s: can't allocate memory for upcall!\n", __func__);
+                return;
+        }
+        nfsd4_umh_cltrack_upcall("create", hexid);
+        kfree(hexid);
+}
+
+static void
+nfsd4_umh_cltrack_remove(struct nfs4_client *clp)
+{
+        char *hexid;
+
+        hexid = bin_to_hex_dup(clp->cl_name.data, clp->cl_name.len);
+        if (!hexid) {
+                dprintk("%s: can't allocate memory for upcall!\n", __func__);
+                return;
+        }
+        nfsd4_umh_cltrack_upcall("remove", hexid);
+        kfree(hexid);
+}
+
+static int
+nfsd4_umh_cltrack_check(struct nfs4_client *clp)
+{
+        int ret;
+        char *hexid;
+
+        hexid = bin_to_hex_dup(clp->cl_name.data, clp->cl_name.len);
+        if (!hexid) {
+                dprintk("%s: can't allocate memory for upcall!\n", __func__);
+                return -ENOMEM;
+        }
+        ret = nfsd4_umh_cltrack_upcall("check", hexid);
+        kfree(hexid);
+        return ret;
+}
+
+static void
+nfsd4_umh_cltrack_grace_done(struct net __attribute__((unused)) *net,
+                                time_t boot_time)
+{
+        char timestr[22]; /* FIXME: better way to determine max size? */
+
+        sprintf(timestr, "%ld", boot_time);
+        nfsd4_umh_cltrack_upcall("gracedone", timestr);
+}
+
+static struct nfsd4_client_tracking_ops nfsd4_umh_tracking_ops = {
+        .init           = nfsd4_umh_cltrack_init,
+        .exit           = NULL,
+        .create         = nfsd4_umh_cltrack_create,
+        .remove         = nfsd4_umh_cltrack_remove,
+        .check          = nfsd4_umh_cltrack_check,
+        .grace_done     = nfsd4_umh_cltrack_grace_done,
+};
+
 int
 nfsd4_client_tracking_init(struct net *net)
 {
@@ -957,7 +1088,8 @@ void
 nfsd4_client_tracking_exit(struct net *net)
 {
         if (client_tracking_ops) {
-                client_tracking_ops->exit(net);
+                if (client_tracking_ops->exit)
+                        client_tracking_ops->exit(net);
                 client_tracking_ops = NULL;
         }
 }