[PATCH v4 1/1] NFSv4.2: condition READDIR's mask for security label based on LSM state

[Olga Kornievskaia <olga.kornievskaia@gmail.com>]

From: Olga Kornievskaia <kolga@netapp.com>

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.

v4: simplifying logic
v3: changing label's initialization per Ondrej's comment
v2: dropping selinux hook and using the sb cap.

Suggested-by: Ondrej Mosnacek <omosnace@redhat.com>
Suggested-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
---
 fs/nfs/nfs4proc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 9e0ca9b2b210..ea72202887c0 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -4966,7 +4966,6 @@ static int _nfs4_proc_readdir(struct dentry *dentry, const struct cred *cred,
 		.pages = pages,
 		.pgbase = 0,
 		.count = count,
-		.bitmask = NFS_SERVER(d_inode(dentry))->attr_bitmask,
 		.plus = plus,
 	};
 	struct nfs4_readdir_res res;
@@ -4981,6 +4980,11 @@ static int _nfs4_proc_readdir(struct dentry *dentry, const struct cred *cred,
 	dprintk("%s: dentry = %pd2, cookie = %Lu\n", __func__,
 			dentry,
 			(unsigned long long)cookie);
+	if (!(NFS_SERVER(d_inode(dentry))->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);
-- 
2.18.2