NFS: add checks for returned value of try_module_get()

There is a couple of places in client code where returned value
of try_module_get() is ignored. As a result there is a small chance
to premature unload module because of unbalanced refcounting.

The patch adds error handling in that places.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 168aa0df2658..b7bfa2765370 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -110,8 +110,8 @@ struct nfs_subversion *get_nfs_version(unsigned int version)
                 mutex_unlock(&nfs_version_mutex);
         }
 
-        if (!IS_ERR(nfs))
-                try_module_get(nfs->owner);
+        if (!IS_ERR(nfs) && !try_module_get(nfs->owner))
+                return ERR_PTR(-EAGAIN);
         return nfs;
 }
 
@@ -158,7 +158,8 @@ struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_init)
                 goto error_0;
 
         clp->cl_nfs_mod = cl_init->nfs_mod;
-        try_module_get(clp->cl_nfs_mod->owner);
+        if (!try_module_get(clp->cl_nfs_mod->owner))
+                goto error_dealloc;
 
         clp->rpc_ops = clp->cl_nfs_mod->rpc_ops;
 
@@ -190,6 +191,7 @@ struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_init)
 
 error_cleanup:
         put_nfs_version(clp->cl_nfs_mod);
+error_dealloc:
         kfree(clp);
 error_0:
         return ERR_PTR(err);