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SubjectRe: [PATCH 2/6] ima: Return INTEGRITY_FAIL if digital signature can't be verified
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On Thu, 2013-02-14 at 14:55 -0500, Vivek Goyal wrote:
> Digital signature verification happens using integrity_digsig_verify().
> Curently we set integrity to FAIL for all error codes except -EOPNOTSUPP.
> This sounds out of line.
>
> - If appropriate kernel code is not compiled in to verify signature of
> a file, then prractically it is a failed signature.
>
> - For so many other possible errors we are setting the status to fail.
> For example, -EINVAL, -ENOKEY, -ENOMEM, -EINVAL, -ENOTSUPP etc, it
> beats me that why -EOPNOTSUPP is special.
>
> This patch should make the semantics more consistent. That is, if digital
> signature is present in security.ima, then any error happened during
> signature processing leads to status INTEGRITY_FAIL.
>
> AFAICS, it should not have any user visible effect on existing
> application. In some cases we will start returning INTEGRITY_FAIL
> instead of INTEGRITY_UNKNOWN. And process_measurement() will deny access
> to file both in case of INTEGRITY_UNKNOWN and INTEGRITY_FAIL.
>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

A number of patches in this patchset more finely differentiate return
codes, which is good. I agree with you totally that there is no good
reason for -EOPNOTSUPP to be handled differently. Unfortunately, the
initramfs is CPIO, which doesn't support xattrs. With the proposed
change and 'ima_appraise_tcb' flag enabled, we wouldn't be able to boot.
I really dislike hard coding policy in the kernel.

thanks,

Mimi

> ---
> security/integrity/ima/ima_appraise.c | 4 +---
> 1 files changed, 1 insertions(+), 3 deletions(-)
>
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 3710f44..6f1eeb8 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -178,9 +178,7 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
> xattr_value->digest, rc - 1,
> iint->ima_xattr.digest,
> IMA_DIGEST_SIZE);
> - if (rc == -EOPNOTSUPP) {
> - status = INTEGRITY_UNKNOWN;
> - } else if (rc) {
> + if (rc) {
> cause = "invalid-signature";
> status = INTEGRITY_FAIL;
> } else {





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