nfs: fix UAF on pathwalk running into umount

NFS ->d_revalidate(), ->permission() and ->get_link() need to access
some parts of nfs_server when called in RCU mode:
	server->flags
	server->caps
	*(server->io_stats)
and, worst of all, call
	server->nfs_client->rpc_ops->have_delegation
(the last one - as NFS_PROTO(inode)->have_delegation()).  We really
don't want to RCU-delay the entire nfs_free_server() (it would have
to be done with schedule_work() from RCU callback, since it can't
be made to run from interrupt context), but actual freeing of
nfs_server and ->io_stats can be done via call_rcu() just fine.
nfs_client part is handled simply by making nfs_free_client() use
kfree_rcu().

Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 44eca51b28085d9deff764bfe6f9286388e93983..fbdc9ca80f714bdf3d3cad54e63d7c858612e5f1 100644 (file)
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -246,7 +246,7 @@ void nfs_free_client(struct nfs_client *clp)
        put_nfs_version(clp->cl_nfs_mod);
        kfree(clp->cl_hostname);
        kfree(clp->cl_acceptor);
-       kfree(clp);
+       kfree_rcu(clp, rcu);
 }
 EXPORT_SYMBOL_GPL(nfs_free_client);
 
@@ -1006,6 +1006,14 @@ struct nfs_server *nfs_alloc_server(void)
 }
 EXPORT_SYMBOL_GPL(nfs_alloc_server);
 
+static void delayed_free(struct rcu_head *p)
+{
+       struct nfs_server *server = container_of(p, struct nfs_server, rcu);
+
+       nfs_free_iostats(server->io_stats);
+       kfree(server);
+}
+
 /*
  * Free up a server record
  */
@@ -1031,10 +1039,9 @@ void nfs_free_server(struct nfs_server *server)
 
        ida_destroy(&server->lockowner_id);
        ida_destroy(&server->openowner_id);
-       nfs_free_iostats(server->io_stats);
        put_cred(server->cred);
-       kfree(server);
        nfs_release_automount_timer();
+       call_rcu(&server->rcu, delayed_free);
 }
 EXPORT_SYMBOL_GPL(nfs_free_server);
 

diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index cd797e00fe359a91b44b2e012309e87d5b446a7e..92de074e63b98c03cefbb2f07d60de0b8f1fb039 100644 (file)
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -124,6 +124,7 @@ struct nfs_client {
        char                    cl_ipaddr[48];
        struct net              *cl_net;
        struct list_head        pending_cb_stateids;
+       struct rcu_head         rcu;
 };
 
 /*
@@ -265,6 +266,7 @@ struct nfs_server {
        const struct cred       *cred;
        bool                    has_sec_mnt_opts;
        struct kobject          kobj;
+       struct rcu_head         rcu;
 };
 
 /* Server capabilities */