SUNRPC: Fix a race in rpc_info_open

There is a race between rpc_info_open and rpc_release_client()
in that nothing stops a process from opening the file after
the clnt->cl_kref goes to zero.

Fix this by using atomic_inc_unless_zero()...

Reported-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org

diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index 569dc72..85f38a6 100644 (file)
--- a/include/linux/sunrpc/clnt.h
+++ b/include/linux/sunrpc/clnt.h
@@ -30,7 +30,7 @@ struct rpc_inode;
  * The high-level client handle
  */
 struct rpc_clnt {
-       struct kref             cl_kref;        /* Number of references */
+       atomic_t                cl_count;       /* Number of references */
        struct list_head        cl_clients;     /* Global list of clients */
        struct list_head        cl_tasks;       /* List of tasks */
        spinlock_t              cl_lock;        /* spinlock */

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 657aac6..3a8f53e 100644 (file)
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -226,7 +226,7 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
                        goto out_no_principal;
        }
 
-       kref_init(&clnt->cl_kref);
+       atomic_set(&clnt->cl_count, 1);
 
        err = rpc_setup_pipedir(clnt, program->pipe_dir_name);
        if (err < 0)
@@ -390,14 +390,14 @@ rpc_clone_client(struct rpc_clnt *clnt)
                if (new->cl_principal == NULL)
                        goto out_no_principal;
        }
-       kref_init(&new->cl_kref);
+       atomic_set(&new->cl_count, 1);
        err = rpc_setup_pipedir(new, clnt->cl_program->pipe_dir_name);
        if (err != 0)
                goto out_no_path;
        if (new->cl_auth)
                atomic_inc(&new->cl_auth->au_count);
        xprt_get(clnt->cl_xprt);
-       kref_get(&clnt->cl_kref);
+       atomic_inc(&clnt->cl_count);
        rpc_register_client(new);
        rpciod_up();
        return new;
@@ -465,10 +465,8 @@ EXPORT_SYMBOL_GPL(rpc_shutdown_client);
  * Free an RPC client
  */
 static void
-rpc_free_client(struct kref *kref)
+rpc_free_client(struct rpc_clnt *clnt)
 {
-       struct rpc_clnt *clnt = container_of(kref, struct rpc_clnt, cl_kref);
-
        dprintk("RPC:       destroying %s client for %s\n",
                        clnt->cl_protname, clnt->cl_server);
        if (!IS_ERR(clnt->cl_path.dentry)) {
@@ -495,12 +493,10 @@ out_free:
  * Free an RPC client
  */
 static void
-rpc_free_auth(struct kref *kref)
+rpc_free_auth(struct rpc_clnt *clnt)
 {
-       struct rpc_clnt *clnt = container_of(kref, struct rpc_clnt, cl_kref);
-
        if (clnt->cl_auth == NULL) {
-               rpc_free_client(kref);
+               rpc_free_client(clnt);
                return;
        }
 
@@ -509,10 +505,11 @@ rpc_free_auth(struct kref *kref)
         *       release remaining GSS contexts. This mechanism ensures
         *       that it can do so safely.
         */
-       kref_init(kref);
+       atomic_inc(&clnt->cl_count);
        rpcauth_release(clnt->cl_auth);
        clnt->cl_auth = NULL;
-       kref_put(kref, rpc_free_client);
+       if (atomic_dec_and_test(&clnt->cl_count))
+               rpc_free_client(clnt);
 }
 
 /*
@@ -525,7 +522,8 @@ rpc_release_client(struct rpc_clnt *clnt)
 
        if (list_empty(&clnt->cl_tasks))
                wake_up(&destroy_wait);
-       kref_put(&clnt->cl_kref, rpc_free_auth);
+       if (atomic_dec_and_test(&clnt->cl_count))
+               rpc_free_auth(clnt);
 }
 
 /**
@@ -588,7 +586,7 @@ void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
        if (clnt != NULL) {
                rpc_task_release_client(task);
                task->tk_client = clnt;
-               kref_get(&clnt->cl_kref);
+               atomic_inc(&clnt->cl_count);
                if (clnt->cl_softrtry)
                        task->tk_flags |= RPC_TASK_SOFT;
                /* Add to the client's list of all tasks */

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 41a762f..8c8eef2 100644 (file)
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -371,21 +371,23 @@ rpc_show_info(struct seq_file *m, void *v)
 static int
 rpc_info_open(struct inode *inode, struct file *file)
 {
-       struct rpc_clnt *clnt;
+       struct rpc_clnt *clnt = NULL;
        int ret = single_open(file, rpc_show_info, NULL);
 
        if (!ret) {
                struct seq_file *m = file->private_data;
-               mutex_lock(&inode->i_mutex);
-               clnt = RPC_I(inode)->private;
-               if (clnt) {
-                       kref_get(&clnt->cl_kref);
+
+               spin_lock(&file->f_path.dentry->d_lock);
+               if (!d_unhashed(file->f_path.dentry))
+                       clnt = RPC_I(inode)->private;
+               if (clnt != NULL && atomic_inc_not_zero(&clnt->cl_count)) {
+                       spin_unlock(&file->f_path.dentry->d_lock);
                        m->private = clnt;
                } else {
+                       spin_unlock(&file->f_path.dentry->d_lock);
                        single_release(inode, file);
                        ret = -EINVAL;
                }
-               mutex_unlock(&inode->i_mutex);
        }
        return ret;
 }