kernfs: move kernfs_xattr_handlers to .rodata

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

Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Signed-off-by: Wedson Almeida Filho <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Acked-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

fs/kernfs/inode.c

···
 	.set = kernfs_vfs_user_xattr_set,
 };
 
-const struct xattr_handler *kernfs_xattr_handlers[] = {
+const struct xattr_handler * const kernfs_xattr_handlers[] = {
 	&kernfs_trusted_xattr_handler,
 	&kernfs_security_xattr_handler,
 	&kernfs_user_xattr_handler,

fs/kernfs/kernfs-internal.h

···
 /*
  * inode.c
  */
-extern const struct xattr_handler *kernfs_xattr_handlers[];
+extern const struct xattr_handler * const kernfs_xattr_handlers[];
 void kernfs_evict_inode(struct inode *inode);
 int kernfs_iop_permission(struct mnt_idmap *idmap,
 			  struct inode *inode, int mask);