Messages in this thread | | | Date | Thu, 31 Oct 2013 15:18:03 +0200 | From | Dmitry Kasatkin <> | Subject | Re: [PATCH] ima: define '_ima' as a builtin 'trusted' keyring |
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On 31/10/13 14:43, Mimi Zohar wrote: > On Thu, 2013-10-31 at 14:23 +0200, Dmitry Kasatkin wrote: >> On 31/10/13 14:03, Mimi Zohar wrote: >>> On Thu, 2013-10-31 at 10:30 +0200, Dmitry Kasatkin wrote: >>>> On 30/10/13 20:54, Mimi Zohar wrote: >>>>> Require all keys added to the IMA keyring be signed by an >>>>> existing trusted key on the system trusted keyring. >>>>> >>>>> Changelog: >>>>> - define stub integrity_init_keyring() function (reported-by Fengguang Wu) >>>>> - differentiate between regular and trusted keyring names. >>>>> - replace printk with pr_info (D. Kasatkin) >>>>> >>>>> Signed-off-by: Mimi Zohar <zohar@us.ibm.com> >>>>> --- >>>>> security/integrity/digsig.c | 30 +++++++++++++++++++++++++++++- >>>>> security/integrity/ima/Kconfig | 8 ++++++++ >>>>> security/integrity/ima/ima_appraise.c | 11 +++++++++++ >>>>> security/integrity/integrity.h | 7 +++++++ >>>>> 4 files changed, 55 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c >>>>> index b4af4eb..77ca965 100644 >>>>> --- a/security/integrity/digsig.c >>>>> +++ b/security/integrity/digsig.c >>>>> @@ -13,7 +13,9 @@ >>>>> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt >>>>> >>>>> #include <linux/err.h> >>>>> +#include <linux/sched.h> >>>>> #include <linux/rbtree.h> >>>>> +#include <linux/cred.h> >>>>> #include <linux/key-type.h> >>>>> #include <linux/digsig.h> >>>>> >>>>> @@ -21,11 +23,19 @@ >>>>> >>>>> static struct key *keyring[INTEGRITY_KEYRING_MAX]; >>>>> >>>>> +#ifdef CONFIG_IMA_TRUSTED_KEYRING >>>>> +static const char *keyring_name[INTEGRITY_KEYRING_MAX] = { >>>>> + ".evm", >>>>> + ".module", >>>>> + ".ima", >>>>> +}; >>>>> +#else >>>>> static const char *keyring_name[INTEGRITY_KEYRING_MAX] = { >>>>> "_evm", >>>>> "_module", >>>>> "_ima", >>>>> }; >>>>> +#endif >>>> Hello, >>>> >>>> I am not sure if having 2 different names "_" and "." makes sense. >>> The existing keyring implementation permits userspace to create a new >>> keyring with the exact same name as a previously defined trusted >>> keyring. For all practical purposes, replacing a trusted keyring with >>> an untrusted one. The existing solution is to prohibit userspace from >>> creating a dot prefixed keyring. >>> >>> Allowing only signed keys to be added to the IMA keyring breaks the >>> existing userspace/kernel ABI, which has existed since linux-3.3. At >>> some point, we could deprecate the non trusted keyring. >>> >>>> Setting trusted-only makes sense until we will get support of setting >>>> trusted only from user-space using keyctl... >>> Agreed, userspace should be permitted to create a trusted keyring, but >>> not change an existing keyring to trusted. >> Then all keys on that keyring must be signed.. >> This is not what I was saying... >> >> It is always possible to specify keyring hierarchy and rules what >> verifies what. >> But may be better not to over-engineer... >> >> It is how it is now.. Will see based on use-cases in the future... > Right, keys can be loaded onto the existing keyring; and the keyring can > be locked in the initramfs. Moving forward, a trusted keyring implies a > HW based certificate chain of trust. > >>>> David, do you remember our discussion in Edinburgh? >>>> Can you provide a way to set keyring as trusted-only from user space.. >>>> >>>> Motivation... >>>> >>>> In many embedded systems, initramfs is built into the kernel image. >>>> Kernel image is signed and obviously initramfs as well.. >>>> Or initramfs may be signed separately like in my prototype implementation... >>>> Note that non-x86 systems - embedded, mobile, etc has no UEFI, MOK. >>>> Initial keys cannot be verified. (we should not rely on using kernel >>>> modules key) >>>> Thus keys on the protected initramfs may not be required to be signed.. >>> In the builtin initramfs case, the public key is included in the signed >>> image. Where is the key stored that verifies the separately signed >>> initramfs? Is there a signature chain of trust? >> In prototype implementation I used kernel module verification >> function... module key... > This implies that you rebuilt the kernel. :) In that case, add your > local-ca public key to the root build tree. All .x509 suffixed files > are included in the image and loaded on the system keyring. >
No.. Key stays on the filesystem... It is re-generated if it is missing...
- Dmitry
>>> If there is a signature chain of trust and a local-ca signed the >>> initramfs, then the local-ca key could be added to the system keyring >>> and used to sign keys for the IMA keyring. >>> >>> thanks, >> You need to embed local-ca somehow into the kernel.. >> Or pass/read and verify it somehow... > Exactly. > > Mimi > >
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