Messages in this thread | | | Subject | Re: [PATCH 03/11] evm: Refuse EVM_ALLOW_METADATA_WRITES only if the HMAC key is loaded | From | Mimi Zohar <> | Date | Fri, 21 Aug 2020 16:14:36 -0400 |
| |
Hi Roberto,
On Thu, 2020-06-18 at 18:01 +0200, Roberto Sassu wrote: > 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. >
Why is the existing hebavior a problem? What is the problem being solved?
> 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;
>
Documentation/ABI/testing/evm needs to be updated as well.
thanks,
Mimi
| |