@@ -42,8 +42,10 @@ Description:
modification of EVM-protected metadata and
disable all further modification of policy
- Note that once a key has been loaded, it will no longer be
- possible to enable metadata modification.
+ Note that once HMAC validation and creation is enabled,
+ it will no longer be possible to enable metadata modification
+ and if metadata modification is already enabled, it will be
+ disabled.
Until key loading has been signaled EVM can not create
or validate the 'security.evm' xattr, but returns
@@ -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;
EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be set to temporarily disable metadata verification until all xattrs/attrs necessary to verify an EVM portable signature are copied to the file. This flag is cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is calculated on unverified xattrs/attrs. Currently EVM unnecessarily denies setting this flag if EVM is initialized with public key, which is not a concern as it cannot be used to trust xattrs/attrs updates. This patch removes this limitation. 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> --- Documentation/ABI/testing/evm | 6 ++++-- security/integrity/evm/evm_secfs.c | 2 +- 2 files changed, 5 insertions(+), 3 deletions(-)