[PATCH 03/11] evm: Refuse EVM_ALLOW_METADATA_WRITES only if the HMAC key is loaded
From: Roberto Sassu <roberto.sassu@huawei.com>
Date: 2020-06-18 16:04:24
Also in:
linux-integrity, lkml, stable
Subsystem:
extended verification module (evm), integrity measurement architecture (ima), security subsystem, the rest · Maintainers:
Mimi Zohar, Roberto Sassu, Dmitry Kasatkin, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
Granting metadata write is safe if the HMAC key is not loaded, as it won't
let an attacker obtain a valid HMAC from corrupted xattrs. evm_write_key()
however does not allow it if any key is loaded, including a public key,
which should not be a problem.
This patch allows setting EVM_ALLOW_METADATA_WRITES if the EVM_INIT_HMAC
flag is not set.
Cc: stable@vger.kernel.org # 4.16.x
Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-protected metadata")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
security/integrity/evm/evm_secfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
index cfc3075769bb..92fe26ace797 100644
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c@@ -84,7 +84,7 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf, * keys are loaded. */ if ((i & EVM_ALLOW_METADATA_WRITES) && - ((evm_initialized & EVM_KEY_MASK) != 0) && + ((evm_initialized & EVM_INIT_HMAC) != 0) && !(evm_initialized & EVM_ALLOW_METADATA_WRITES)) return -EPERM;
--
2.17.1