evm: Translate user/group ids relative to s_user_ns when computing HMAC

The EVM HMAC should be calculated using the on disk user and
group ids, so the k[ug]ids in the inode must be translated
relative to the s_user_ns of the inode's super block.
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

security/integrity/evm/evm_crypto.c

@@ -151,8 +151,8 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 	memset(&hmac_misc, 0, sizeof(hmac_misc));
 	hmac_misc.ino = inode->i_ino;
 	hmac_misc.generation = inode->i_generation;
-	hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
-	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
+	hmac_misc.uid = from_kuid(inode->i_sb->s_user_ns, inode->i_uid);
+	hmac_misc.gid = from_kgid(inode->i_sb->s_user_ns, inode->i_gid);
 	hmac_misc.mode = inode->i_mode;
 	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 	if (evm_hmac_attrs & EVM_ATTR_FSUUID)