nfs: move nfs4_xattr_handlers to .rodata

This makes it harder for accidental or malicious changes to
nfs4_xattr_handlers at runtime.

Cc: Trond Myklebust <[e-mail]>
Cc: Anna Schumaker <[e-mail]>
Cc: [e-mail]
Signed-off-by: Wedson Almeida Filho <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

fs/nfs/nfs.h

···
 	const struct rpc_version *rpc_vers;	/* NFS version information */
 	const struct nfs_rpc_ops *rpc_ops;	/* NFS operations */
 	const struct super_operations *sops;	/* NFS Super operations */
-	const struct xattr_handler **xattr;	/* NFS xattr handlers */
+	const struct xattr_handler * const *xattr;	/* NFS xattr handlers */
 	struct list_head list;		/* List of NFS versions */
 };
 

fs/nfs/nfs4_fs.h

···
 						    struct nfs_fh *,
 						    struct nfs_fattr *);
 extern int nfs4_proc_secinfo(struct inode *, const struct qstr *, struct nfs4_secinfo_flavors *);
-extern const struct xattr_handler *nfs4_xattr_handlers[];
+extern const struct xattr_handler * const nfs4_xattr_handlers[];
 extern int nfs4_set_rw_stateid(nfs4_stateid *stateid,
 		const struct nfs_open_context *ctx,
 		const struct nfs_lock_context *l_ctx,

fs/nfs/nfs4proc.c

···
 };
 #endif
 
-const struct xattr_handler *nfs4_xattr_handlers[] = {
+const struct xattr_handler * const nfs4_xattr_handlers[] = {
 	&nfs4_xattr_nfs4_acl_handler,
 #if defined(CONFIG_NFS_V4_1)
 	&nfs4_xattr_nfs4_dacl_handler,