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

3 files changed, 21 insertions, 21 deletions

diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index 569dc722a600..85f38a63f098 100644
--- 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 657aac630fc9..3a8f53e7ba07 100644
--- 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 41a762f82630..8c8eef2b8f26 100644
--- 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;
 }