nfs4: take a reference on the nfs_client when running FREE_STATEID

During umount, the session slot tables are freed.  If there are
outstanding FREE_STATEID tasks, a use-after-free and slab corruption can
occur when rpc_exit_task calls rpc_call_done -> nfs41_sequence_done ->
nfs4_sequence_process/nfs41_sequence_free_slot.

Prevent that from happening by taking a reference on the nfs_client in
nfs41_free_stateid and putting it in nfs41_free_stateid_release.

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 1c94f54cab58aaec0492c22bb80fde75bc91ae14..127388fabda875011ccf67e445921347895f6597 100644 (file)
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -10115,6 +10115,10 @@ static void nfs41_free_stateid_done(struct rpc_task *task, void *calldata)
 
 static void nfs41_free_stateid_release(void *calldata)
 {
+       struct nfs_free_stateid_data *data = calldata;
+       struct nfs_client *clp = data->server->nfs_client;
+
+       nfs_put_client(clp);
        kfree(calldata);
 }
 
@@ -10151,6 +10155,10 @@ static int nfs41_free_stateid(struct nfs_server *server,
        };
        struct nfs_free_stateid_data *data;
        struct rpc_task *task;
+       struct nfs_client *clp = server->nfs_client;
+
+       if (!refcount_inc_not_zero(&clp->cl_count))
+               return -EIO;
 
        nfs4_state_protect(server->nfs_client, NFS_SP4_MACH_CRED_STATEID,
                &task_setup.rpc_client, &msg);