[PATCH v3] nfs: protect nfs41_impl_id by rcu

[Li Lingfeng <lilingfeng3@huawei.com>]

When performing exchange id call, a new nfs41_impl_id will be allocated to
store some information from server. The pointers to the old and new
nfs41_impl_ids are swapped, and the old one will be freed.

However, UAF may be triggered as follows:

After T2 has got a pointer to the nfs41_impl_id, the nfs41_impl_id is
freed by T1 before it is used.
         T1                                           T2
nfs4_proc_exchange_id
 _nfs4_proc_exchange_id
  nfs4_run_exchange_id
   kzalloc // alloc nfs41_impl_id-B
   rpc_run_task
                                nfs_show_stats
                                 show_implementation_id
                                  impl_id = nfss->nfs_client->cl_implid
                                  // get alloc nfs41_impl_id-A
  swap(clp->cl_implid, resp->impl_id)
  rpc_put_task
   ...
    nfs4_exchange_id_release
     kfree // free nfs41_impl_id-A
                                  impl_id->name // UAF

Fix this issue by using rcu to protect the nfs41_impl_id.

Fixes: 7d2ed9ac22bc ("NFSv4: parse and display server implementation ids")
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
---
v1->v2:
  Free nfs41_impl_id by call_rcu in nfs4_shutdown_client to resolve
  warning.
v2->v3:
  Free nfs41_impl_id by kfree_rcu and check CONFIG_NFS_V4_1 before
  freeing nfs41_impl_id in nfs4_shutdown_client.

 fs/nfs/nfs4client.c       |  5 ++++-
 fs/nfs/nfs4proc.c         |  5 +++--
 fs/nfs/super.c            | 12 +++++++++---
 include/linux/nfs_fs_sb.h |  2 +-
 include/linux/nfs_xdr.h   |  3 ++-
 5 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 83378f69b35e..852a64294fec 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -293,7 +293,10 @@ static void nfs4_shutdown_client(struct nfs_client *clp)
 	rpc_destroy_wait_queue(&clp->cl_rpcwaitq);
 	kfree(clp->cl_serverowner);
 	kfree(clp->cl_serverscope);
-	kfree(clp->cl_implid);
+#ifdef CONFIG_NFS_V4_1
+	if (clp->cl_implid)
+		kfree_rcu(clp->cl_implid, __rcu_head);
+#endif
 	kfree(clp->cl_owner_id);
 }
 
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index cd2fbde2e6d7..b6a9bcabb531 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -8884,7 +8884,8 @@ static void nfs4_exchange_id_release(void *data)
 					(struct nfs41_exchange_id_data *)data;
 
 	nfs_put_client(cdata->args.client);
-	kfree(cdata->res.impl_id);
+	if (cdata->res.impl_id)
+		kfree_rcu(cdata->res.impl_id, __rcu_head);
 	kfree(cdata->res.server_scope);
 	kfree(cdata->res.server_owner);
 	kfree(cdata);
@@ -9046,7 +9047,7 @@ static int _nfs4_proc_exchange_id(struct nfs_client *clp, const struct cred *cre
 
 	swap(clp->cl_serverowner, resp->server_owner);
 	swap(clp->cl_serverscope, resp->server_scope);
-	swap(clp->cl_implid, resp->impl_id);
+	resp->impl_id = rcu_replace_pointer(clp->cl_implid, resp->impl_id, 1);
 
 	/* Save the EXCHANGE_ID verifier session trunk tests */
 	memcpy(clp->cl_confirm.data, argp->verifier.data,
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 9723b6c53397..57665a82f12b 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -615,13 +615,19 @@ static void show_pnfs(struct seq_file *m, struct nfs_server *server)
 
 static void show_implementation_id(struct seq_file *m, struct nfs_server *nfss)
 {
-	if (nfss->nfs_client && nfss->nfs_client->cl_implid) {
-		struct nfs41_impl_id *impl_id = nfss->nfs_client->cl_implid;
+	struct nfs_client *clp = nfss->nfs_client;
+	struct nfs41_impl_id *impl_id;
+
+	if (!clp)
+		return;
+	rcu_read_lock();
+	impl_id = rcu_dereference(clp->cl_implid);
+	if (impl_id)
 		seq_printf(m, "\n\timpl_id:\tname='%s',domain='%s',"
 			   "date='%llu,%u'",
 			   impl_id->name, impl_id->domain,
 			   impl_id->date.seconds, impl_id->date.nseconds);
-	}
+	rcu_read_unlock();
 }
 #else
 #if IS_ENABLED(CONFIG_NFS_V4)
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index b804346a9741..fcad3f0ea68b 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -104,7 +104,7 @@ struct nfs_client {
 	bool			cl_preserve_clid;
 	struct nfs41_server_owner *cl_serverowner;
 	struct nfs41_server_scope *cl_serverscope;
-	struct nfs41_impl_id	*cl_implid;
+	struct nfs41_impl_id __rcu *cl_implid;
 	/* nfs 4.1+ state protection modes: */
 	unsigned long		cl_sp4_flags;
 #define NFS_SP4_MACH_CRED_MINIMAL  1	/* Minimal sp4_mach_cred - state ops
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 12d8e47bc5a3..a9d8a58ddb7c 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1374,6 +1374,7 @@ struct nfs41_impl_id {
 	char				domain[NFS4_OPAQUE_LIMIT + 1];
 	char				name[NFS4_OPAQUE_LIMIT + 1];
 	struct nfstime4			date;
+	struct rcu_head			__rcu_head;
 };
 
 #define MAX_BIND_CONN_TO_SESSION_RETRIES 3
@@ -1397,7 +1398,7 @@ struct nfs41_exchange_id_res {
 	u32				flags;
 	struct nfs41_server_owner	*server_owner;
 	struct nfs41_server_scope	*server_scope;
-	struct nfs41_impl_id		*impl_id;
+	struct nfs41_impl_id __rcu	*impl_id;
 	struct nfs41_state_protection	state_protect;
 };
 
-- 
2.31.1