> From: Mimi Zohar [mailto:zohar@xxxxxxxxxxxxx] > Sent: Monday, May 3, 2021 3:00 PM > On Wed, 2021-04-07 at 12:52 +0200, Roberto Sassu wrote: > > > diff --git a/security/integrity/evm/evm_main.c > b/security/integrity/evm/evm_main.c > > @@ -389,6 +473,11 @@ static int evm_protect_xattr(struct > user_namespace *mnt_userns, > > if (evm_status == INTEGRITY_FAIL_IMMUTABLE) > > return 0; > > > > + if (evm_status == INTEGRITY_PASS_IMMUTABLE && > > + !evm_xattr_change(mnt_userns, dentry, xattr_name, xattr_value, > > + xattr_value_len)) > > + return 0; > > + > > If the purpose of evm_protect_xattr() is to prevent allowing an invalid > security.evm xattr from being re-calculated and updated, making it > valid, INTEGRITY_PASS_IMMUTABLE shouldn't need to be conditional. Any > time there is an attr or xattr change, including setting it to the > existing value, the status flag should be reset. The status is always reset if evm_protect_xattr() returns 0. This does not change. Not making INTEGRITY_PASS_IMMUTABLE conditional would cause issues. Suppose that the status is INTEGRITY_FAIL. Writing the same xattr would cause evm_protect_xattr() to return 0 and the HMAC to be updated. > I'm wondering if making INTEGRITY_PASS_IMMUTABLE conditional would > prevent the file from being resigned. INTEGRITY_FAIL_IMMUTABLE should be enough to continue the operation. Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > > if (evm_status != INTEGRITY_PASS) > > integrity_audit_msg(AUDIT_INTEGRITY_METADATA, > d_backing_inode(dentry), > > dentry->d_name.name, > "appraise_metadata", > > This would then be updated to if not INTEGRITY_PASS or > INTEGRITY_PASS_IMMUTABLE. The subsequent "return" would need to be > updated as well. > > thanks, > > Mimi
