NFSv4.2: condition READDIR's mask for security label based on LSM state

stable inclusion
from linux-4.19.164
commit 2cdde54b6099025db7e870d81ff6e4bb8c98e950

--------------------------------

[ Upstream commit 05ad9175 ]

Currently, the client will always ask for security_labels if the server
returns that it supports that feature regardless of any LSM modules
(such as Selinux) enforcing security policy. This adds performance
penalty to the READDIR operation.

Client adjusts superblock's support of the security_label based on
the server's support but also current client's configuration of the
LSM modules. Thus, prior to using the default bitmask in READDIR,
this patch checks the server's capabilities and then instructs
READDIR to remove FATTR4_WORD2_SECURITY_LABEL from the bitmask.

v5: fixing silly mistakes of the rushed v4
v4: simplifying logic
v3: changing label's initialization per Ondrej's comment
v2: dropping selinux hook and using the sb cap.
Suggested-by: NOndrej Mosnacek <omosnace@redhat.com>
Suggested-by: NScott Mayhew <smayhew@redhat.com>
Signed-off-by: NOlga Kornievskaia <kolga@netapp.com>
Fixes: 2b0143b5 ("VFS: normal filesystems (and lustre): d_inode() annotations")
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/nfs/nfs4proc.c

@@ -4678,12 +4678,12 @@ static int _nfs4_proc_readdir(struct dentry *dentry, struct rpc_cred *cred,
 		u64 cookie, struct page **pages, unsigned int count, bool plus)
 {
 	struct inode		*dir = d_inode(dentry);
+	struct nfs_server	*server = NFS_SERVER(dir);
 	struct nfs4_readdir_arg args = {
 		.fh = NFS_FH(dir),
 		.pages = pages,
 		.pgbase = 0,
 		.count = count,
-		.bitmask = NFS_SERVER(d_inode(dentry))->attr_bitmask,
 		.plus = plus,
 	};
 	struct nfs4_readdir_res res;
@@ -4698,9 +4698,15 @@ static int _nfs4_proc_readdir(struct dentry *dentry, struct rpc_cred *cred,
 	dprintk("%s: dentry = %pd2, cookie = %Lu\n", __func__,
 			dentry,
 			(unsigned long long)cookie);
+	if (!(server->caps & NFS_CAP_SECURITY_LABEL))
+		args.bitmask = server->attr_bitmask_nl;
+	else
+		args.bitmask = server->attr_bitmask;
+
 	nfs4_setup_readdir(cookie, NFS_I(dir)->cookieverf, dentry, &args);
 	res.pgbase = args.pgbase;
-	status = nfs4_call_sync(NFS_SERVER(dir)->client, NFS_SERVER(dir), &msg, &args.seq_args, &res.seq_res, 0);
+	status = nfs4_call_sync(server->client, server, &msg, &args.seq_args,
+			&res.seq_res, 0);
 	if (status >= 0) {
 		memcpy(NFS_I(dir)->cookieverf, res.verifier.data, NFS4_VERIFIER_SIZE);
 		status += args.pgbase;