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Date: Wed, 28 May 2014 15:26:22 -0400
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc: linux-security-module <linux-security-module@...r.kernel.org>,
Dmitry Kasatkin <d.kasatkin@...sung.com>,
David Howells <dhowells@...hat.com>,
Josh Boyer <jwboyer@...hat.com>,
keyrings <keyrings@...ux-nfs.org>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v4 3/4] ima: define '.ima' as a builtin 'trusted'
keyring
On Wed, 2014-05-28 at 21:55 +0300, Dmitry Kasatkin wrote:
> On 28 May 2014 18:09, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> > Require all keys added to the IMA keyring be signed by an
> > existing trusted key on the system trusted keyring.
> >
> > Changelog v1:
> > - don't link IMA trusted keyring to user 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)
> > - only make the IMA keyring a trusted keyring (reported-by D. Kastatkin)
> > - define stub integrity_init_keyring() definition based on
> > CONFIG_INTEGRITY_SIGNATURE, not CONFIG_INTEGRITY_ASYMMETRIC_KEYS.
> > (reported-by Jim Davis)
> >
> > Signed-off-by: Mimi Zohar<zohar@...ux.vnet.ibm.com>
> > ---
> > security/integrity/digsig.c | 26 +++++++++++++++++++++++++-
> > security/integrity/ima/Kconfig | 8 ++++++++
> > security/integrity/ima/ima_appraise.c | 11 +++++++++++
> > security/integrity/integrity.h | 5 +++++
> > 4 files changed, 49 insertions(+), 1 deletion(-)
> >
> > diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
> > index b4af4eb..7da5f9c 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>
> >
> > @@ -24,7 +26,11 @@ static struct key *keyring[INTEGRITY_KEYRING_MAX];
> > static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
> > "_evm",
> > "_module",
> > +#ifndef CONFIG_IMA_TRUSTED_KEYRING
> > "_ima",
> > +#else
> > + ".ima",
> > +#endif
> > };
> >
> > int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
> > @@ -35,7 +41,7 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
> >
> > if (!keyring[id]) {
> > keyring[id] =
> > - request_key(&key_type_keyring, keyring_name[id], NULL);
> > + request_key(&key_type_keyring, keyring_name[id], NULL);
> > if (IS_ERR(keyring[id])) {
> > int err = PTR_ERR(keyring[id]);
> > pr_err("no %s keyring: %d\n", keyring_name[id], err);
> > @@ -56,3 +62,21 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
> >
> > return -EOPNOTSUPP;
> > }
> > +
> > +int integrity_init_keyring(const unsigned int id)
> > +{
> > + const struct cred *cred = current_cred();
> > +
> > + keyring[id] = keyring_alloc(keyring_name[id], KUIDT_INIT(0),
> > + KGIDT_INIT(0), cred,
> > + ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
> > + KEY_USR_VIEW | KEY_USR_READ |
> > + KEY_USR_WRITE | KEY_USR_SEARCH),
> > + KEY_ALLOC_NOT_IN_QUOTA, NULL);
>
> Last parameter "destination" is NULL. It makes keyring "unsearchable"
> from user space.
> It prevents loading trusted keys from user-space, e.g. initramfs...
>
> Should it be "cred->user->uid_keyring"??
David extended keyctl with the '%keyring' option. For example,
"keyctl show %keyring:.ima" returns the .ima keyring id with a list of
all the keys.
>
>
> > + if (!IS_ERR(keyring[id]))
> > + set_bit(KEY_FLAG_TRUSTED_ONLY, &keyring[id]->flags);
> > + else
> > + pr_info("Can't allocate %s keyring (%ld)\n",
> > + keyring_name[id], PTR_ERR(keyring[id]));
>
> keyring[id] should be set "back" to NULL. Otherwise bad value might be
> used in other places.
Good catch, thanks.
>
> > + return 0;
> > +}
> > diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> > index 81a2797..dad8d4c 100644
> > --- a/security/integrity/ima/Kconfig
> > +++ b/security/integrity/ima/Kconfig
> > @@ -123,3 +123,11 @@ config IMA_APPRAISE
> > For more information on integrity appraisal refer to:
> > <http://linux-ima.sourceforge.net>
> > If unsure, say N.
> > +
> > +config IMA_TRUSTED_KEYRING
> > + bool "Require all keys on the _ima keyring be signed"
> > + depends on IMA_APPRAISE && SYSTEM_TRUSTED_KEYRING
> > + default y
> > + help
> > + This option requires that all keys added to the _ima
> > + keyring be signed by a key on the system trusted keyring.
> > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> > index d3113d4..003ff46 100644
> > --- a/security/integrity/ima/ima_appraise.c
> > +++ b/security/integrity/ima/ima_appraise.c
> > @@ -385,3 +385,14 @@ int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
> > }
> > return result;
> > }
> > +
> > +#ifdef CONFIG_IMA_TRUSTED_KEYRING
> > +static int __init init_ima_keyring(void)
> > +{
> > + int ret;
> > +
> > + ret = integrity_init_keyring(INTEGRITY_KEYRING_IMA);
> > + return 0;
> > +}
> > +late_initcall(init_ima_keyring);
>
>
> late_initcall(init_ima_keyring) ordering competes with late_initcall(init_ima);
> but we want keyring to be initialized before IMA might use it.
> In the case when we would load keys from ima kernel initialization
> code, order is important.
>
> we already have init_ima() and ima_init calls().
> Why not call integrity_init_keyring() from there?
>
> Indeed, we have one late_initcall(init_evm) for EVM, and one
> late_initcall(init_ima) for IMA.
>
> It's enough...
Right, there's no reason to have an additional call.
thanks,
Mimi
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