Messages in this thread | | | Subject | Re: [PATCH 2/2] ima: Support appraise_type=imasig_optional | From | Mimi Zohar <> | Date | Tue, 12 Feb 2013 15:05:36 -0500 |
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On Tue, 2013-02-12 at 13:52 -0500, Vivek Goyal wrote: > On Tue, Feb 12, 2013 at 12:14:07PM -0500, Mimi Zohar wrote: > > [..] > > > > > --- a/security/integrity/ima/ima_appraise.c > > > > > +++ b/security/integrity/ima/ima_appraise.c > > > > > @@ -124,19 +124,26 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint, > > > > > enum integrity_status status = INTEGRITY_UNKNOWN; > > > > > const char *op = "appraise_data"; > > > > > char *cause = "unknown"; > > > > > - int rc; > > > > > + int rc, audit_info = 0; > > > > > > > > > > if (!ima_appraise) > > > > > return 0; > > > > > - if (!inode->i_op->getxattr) > > > > > + if (!inode->i_op->getxattr) { > > > > > + /* getxattr not supported. file couldn't have been signed */ > > > > > + if (iint->flags & IMA_DIGSIG_OPTIONAL) > > > > > + return INTEGRITY_PASS; > > > > > return INTEGRITY_UNKNOWN; > > > > > + } > > > > > > > > > > > > > Please don't change the result of the appraisal like this. A single > > > > change can be made towards the bottom of process_measurement(). > > > > > > I don't want to pass integrity in all cases of INTEGRITY_UNKNOWN. So > > > I can probably maintain a bool variable, say pass_appraisal, and set > > > that here and at the end of function, parse that variable and change > > > the status accordingly. > > > > process_measurement() is the only caller of ima_appraise_measurement(). > > Leave the results of ima_appraise_measurement() alone. There's already > > code at the end of process_measurement() which decides what to return. > > Just modify it based on the appraisal results. > > Ok, I can do that. There is a small concern though. That is what to do > when rc = INTEGRITY_UKNOWN and IMA_DIGSIG_OPTIONAL flag is set. > > ima_appraise_measurement() returns INTEGRITY_UKNOWN when file system > does not support xattrs or if security xattr is not enabled. In this > case it is desirable to allow access if IMA_DIGSIG_OPTIONAL flag is > set.
Right, 'INTEGRITY_UNKNOWN' means that we can't reason, for whatever reason, about the integrity of the file.
> But INTEGRITY_UNKNOWN is also also returned when integrity_digsig_verify() > fails and returns -EOPNOTSUPP.
In this case, it is Kconfig based.
> I feel that in this case it is not very appropriate to pass appraisal and > let executable run. If digital signatures are present but we can't verify > those (Say some algorithm is not supported in kernel). In that case I > think it makes sense to fail the signature. > > rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA, > xattr_value->digest, rc - 1, > iint->ima_xattr.digest, > IMA_DIGEST_SIZE); > if (rc == -EOPNOTSUPP) { > status = INTEGRITY_UNKNOWN; > > > So how to handle this case. > > I am wondering why do we reutrn INTEGRITY_UNKNOWN above and not > INTEGRITY_FAIL.
We still can't reason about the integrity of the file. For all we know, it could be a validly signed file, just verification wasn't enabled.
> Will it make sense to fail signature in case of -EOPNOTSUPP. > rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA, > xattr_value->digest, rc - 1, > iint->ima_xattr.digest, > IMA_DIGEST_SIZE); > if (rc) > status = INTEGRITY_FAIL; > else > status = INTEGRITY_PASS; > >
Please don't.
Mimi
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