On Mon, 2019-06-03 at 16:29 +0200, Roberto Sassu wrote: > On 6/3/2019 3:43 PM, James Bottomley wrote: > > On Mon, 2019-06-03 at 11:25 +0200, Roberto Sassu wrote: > > > On 5/30/2019 2:00 PM, Mimi Zohar wrote: > > > > On Wed, 2019-05-29 at 15:30 +0200, Roberto Sassu wrote: > > > > > Currently, ima_appraise_measurement() ignores the EVM status > > > > > when evm_verifyxattr() returns INTEGRITY_UNKNOWN. If a file > > > > > has a valid security.ima xattr with type IMA_XATTR_DIGEST or > > > > > IMA_XATTR_DIGEST_NG, ima_appraise_measurement() returns > > > > > INTEGRITY_PASS regardless of the EVM status. The problem is > > > > > that the EVM status is overwritten with the appraisal statu > > > > > > > > Roberto, your framing of this problem is harsh and > > > > misleading. IMA and EVM are intentionally independent of each > > > > other and can be configured independently of each other. The > > > > intersection of the two is the call to > > > > evm_verifyxattr(). INTEGRITY_UNKNOWN is > > > > returned for a number of reasons - when EVM is not configured, > > > > the EVM hmac key has not yet been loaded, the protected > > > > security attribute is unknown, or the file is not in policy. > > > > > > > > This patch does not differentiate between any of the above > > > > cases, requiring mutable files to always be protected by EVM, > > > > when specified as an "ima_appraise=" option on the boot command > > > > line. > > > > > > > > IMA could be extended to require EVM on a per IMA policy rule > > > > basis. Instead of framing allowing IMA file hashes without EVM > > > > as a bug that has existed from the very beginning, now that > > > > IMA/EVM have matured and is being used, you could frame it as > > > > extending IMA or hardening. > > > > > > I'm seeing it from the perspective of an administrator that > > > manages an already hardened system, and expects that the system > > > only grants access to files with a valid signature/HMAC. That > > > system would not enforce this behavior if EVM keys are removed > > > and the digest in security.ima is set to the actual file digest. > > > > > > Framing it as a bug rather than an extension would in my opinion > > > help to convince people about the necessity to switch to the safe > > > mode, if their system is already hardened. > > > > I have a use case for IMA where I use it to enforce immutability of > > containers. In this use case, the cluster admin places hashes on > > executables as the image is unpacked so that if an executable file > > is changed, IMA will cause an execution failure. For this use > > case, I don't care about the EVM, in fact we don't use it, because > > the only object is to fail execution if a binary is mutated. > > How would you prevent root in the container from updating > security.ima? We don't. We only guarantee immutability for unprivileged containers, so root can't be inside. James
