NFSv4: Fix NFSv4 reference counting for trunked sessions

The reference counting in nfs4_init_client assumes wongly that it
is safe for nfs4_discover_server_trunking() to return a pointer to a
nfs_client prior to bumping the reference count.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Ben Greear <greearb@candelatech.com>
Cc: stable@vger.kernel.org [>=3.7]

1 files changed, 15 insertions, 16 deletions

diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index acc347268124..65a290a73065 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -236,11 +236,10 @@ struct nfs_client *nfs4_init_client(struct nfs_client *clp,
         error = nfs4_discover_server_trunking(clp, &old);
         if (error < 0)
                 goto error;
+        nfs_put_client(clp);
         if (clp != old) {
                 clp->cl_preserve_clid = true;
-                nfs_put_client(clp);
                 clp = old;
-                atomic_inc(&clp->cl_count);
         }
 
         return clp;
@@ -306,7 +305,7 @@ int nfs40_walk_client_list(struct nfs_client *new,
                 .clientid       = new->cl_clientid,
                 .confirm        = new->cl_confirm,
         };
-        int status;
+        int status = -NFS4ERR_STALE_CLIENTID;
 
         spin_lock(&nn->nfs_client_lock);
         list_for_each_entry_safe(pos, n, &nn->nfs_client_list, cl_share_link) {
@@ -332,28 +331,28 @@ int nfs40_walk_client_list(struct nfs_client *new,
 
                 if (prev)
                         nfs_put_client(prev);
+                prev = pos;
 
                 status = nfs4_proc_setclientid_confirm(pos, &clid, cred);
-                if (status == 0) {
+                switch (status) {
+                case -NFS4ERR_STALE_CLIENTID:
+                        break;
+                case 0:
                         nfs4_swap_callback_idents(pos, new);
 
-                        nfs_put_client(pos);
+                        prev = NULL;
                         *result = pos;
                         dprintk("NFS: <-- %s using nfs_client = %p ({%d})\n",
                                 __func__, pos, atomic_read(&pos->cl_count));
-                        return 0;
-                }
-                if (status != -NFS4ERR_STALE_CLIENTID) {
-                        nfs_put_client(pos);
-                        dprintk("NFS: <-- %s status = %d, no result\n",
-                                __func__, status);
-                        return status;
+                default:
+                        goto out;
                 }
 
                 spin_lock(&nn->nfs_client_lock);
-                prev = pos;
         }
+        spin_unlock(&nn->nfs_client_lock);
 
+out:
         /*
          * No matching nfs_client found.  This should be impossible,
          * because the new nfs_client has already been added to
@@ -363,9 +362,8 @@ int nfs40_walk_client_list(struct nfs_client *new,
          */
         if (prev)
                 nfs_put_client(prev);
-        spin_unlock(&nn->nfs_client_lock);
-        pr_err("NFS: %s Error: no matching nfs_client found\n", __func__);
-        return -NFS4ERR_STALE_CLIENTID;
+        dprintk("NFS: <-- %s status = %d\n", __func__, status);
+        return status;
 }
 
 #ifdef CONFIG_NFS_V4_1
@@ -473,6 +471,7 @@ int nfs41_walk_client_list(struct nfs_client *new,
                 if (!nfs4_match_serverowners(pos, new))
                         continue;
 
+                atomic_inc(&pos->cl_count);
                 spin_unlock(&nn->nfs_client_lock);
                 dprintk("NFS: <-- %s using nfs_client = %p ({%d})\n",
                         __func__, pos, atomic_read(&pos->cl_count));