> On Jun 3, 2019, at 9:43 AM, James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> 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. > > So I can see your use case requires IMA+EVM, but requiring it would > cause more complexity for my use case. ... and would not work at all for the current NFS IMA implementation. -- Chuck Lever
