Re: [RFC PATCH v5 2/4] KEYS: verify a certificate is signed by a 'trusted' key

[Mimi Zohar]

On Mon, 2014-06-09 at 16:13 +0300, Dmitry Kasatkin wrote: 
> On 07/06/14 00:50, Dmitry Kasatkin wrote:
> > On 3 June 2014 20:58, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> >> Only public keys, with certificates signed by an existing
> >> 'trusted' key on the system trusted keyring, should be added
> >> to a trusted keyring.  This patch adds support for verifying
> >> a certificate's signature.
> >>
> >> This is derived from David Howells pkcs7_request_asymmetric_key() patch.
> >>
> >> Changelog:
> >> - define get_system_trusted_keyring() to fix kbuild issues
> >>
> >> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> >> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> > Acked-by: me
> >
> >
> >> ---
> >>  crypto/asymmetric_keys/x509_public_key.c | 84 +++++++++++++++++++++++++++++++-
> >>  include/keys/system_keyring.h            | 10 +++-
> >>  2 files changed, 92 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c
> >> index 382ef0d..1af8a30 100644
> >> --- a/crypto/asymmetric_keys/x509_public_key.c
> >> +++ b/crypto/asymmetric_keys/x509_public_key.c
> >> @@ -18,12 +18,60 @@
> >>  #include <linux/asn1_decoder.h>
> >>  #include <keys/asymmetric-subtype.h>
> >>  #include <keys/asymmetric-parser.h>
> >> +#include <keys/system_keyring.h>
> >>  #include <crypto/hash.h>
> >>  #include "asymmetric_keys.h"
> >>  #include "public_key.h"
> >>  #include "x509_parser.h"
> >>
> >>  /*
> >> + * Find a key in the given keyring by issuer and authority.
> >> + */
> >> +static struct key *x509_request_asymmetric_key(
> >> +       struct key *keyring,
> >> +       const char *signer, size_t signer_len,
> >> +       const char *authority, size_t auth_len)
> >> +{
> >> +       key_ref_t key;
> >> +       char *id;
> >> +
> >> +       /* Construct an identifier. */
> >> +       id = kmalloc(signer_len + 2 + auth_len + 1, GFP_KERNEL);
> >> +       if (!id)
> >> +               return ERR_PTR(-ENOMEM);
> >> +
> >> +       memcpy(id, signer, signer_len);
> >> +       id[signer_len + 0] = ':';
> >> +       id[signer_len + 1] = ' ';
> >> +       memcpy(id + signer_len + 2, authority, auth_len);
> >> +       id[signer_len + 2 + auth_len] = 0;
> >> +
> >> +       pr_debug("Look up: \"%s\"\n", id);
> >> +
> >> +       key = keyring_search(make_key_ref(keyring, 1),
> >> +                            &key_type_asymmetric, id);
> >> +       if (IS_ERR(key))
> >> +               pr_debug("Request for module key '%s' err %ld\n",
> >> +                        id, PTR_ERR(key));
> >> +       kfree(id);
> >> +
> >> +       if (IS_ERR(key)) {
> >> +               switch (PTR_ERR(key)) {
> >> +                       /* Hide some search errors */
> >> +               case -EACCES:
> >> +               case -ENOTDIR:
> >> +               case -EAGAIN:
> >> +                       return ERR_PTR(-ENOKEY);
> >> +               default:
> >> +                       return ERR_CAST(key);
> >> +               }
> >> +       }
> >> +
> >> +       pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
> >> +       return key_ref_to_ptr(key);
> >> +}
> >> +
> >> +/*
> >>   * Set up the signature parameters in an X.509 certificate.  This involves
> >>   * digesting the signed data and extracting the signature.
> >>   */
> >> @@ -103,6 +151,36 @@ int x509_check_signature(const struct public_key *pub,
> >>  EXPORT_SYMBOL_GPL(x509_check_signature);
> >>
> >>  /*
> >> + * Check the new certificate against the ones in the trust keyring.  If one of
> >> + * those is the signing key and validates the new certificate, then mark the
> >> + * new certificate as being trusted.
> >> + *
> >> + * Return 0 if the new certificate was successfully validated, 1 if we couldn't
> >> + * find a matching parent certificate in the trusted list and an error if there
> >> + * is a matching certificate but the signature check fails.
> >> + */
> >> +static int x509_validate_trust(struct x509_certificate *cert,
> >> +                              struct key *trust_keyring)
> >> +{
> >> +       const struct public_key *pk;
> >> +       struct key *key;
> >> +       int ret = 1;
> >> +
> >> +       if (!trust_keyring)
> >> +               return -EOPNOTSUPP;
> >> +
> >> +       key = x509_request_asymmetric_key(trust_keyring,
> >> +                                         cert->issuer, strlen(cert->issuer),
> >> +                                         cert->authority,
> >> +                                         strlen(cert->authority));
> >> +       if (!IS_ERR(key))  {
> >> +               pk = key->payload.data;
> >> +               ret = x509_check_signature(pk, cert);
> >> +       }
> >> +       return ret;
> >> +}
> >> +
> >> +/*
> >>   * Attempt to parse a data blob for a key as an X509 certificate.
> >>   */
> >>  static int x509_key_preparse(struct key_preparsed_payload *prep)
> >> @@ -155,9 +233,13 @@ static int x509_key_preparse(struct key_preparsed_payload *prep)
> >>         /* Check the signature on the key if it appears to be self-signed */
> >>         if (!cert->authority ||
> >>             strcmp(cert->fingerprint, cert->authority) == 0) {
> >> -               ret = x509_check_signature(cert->pub, cert);
> >> +               ret = x509_check_signature(cert->pub, cert); /* self-signed */
> >>                 if (ret < 0)
> >>                         goto error_free_cert;
> >> +       } else {
> >> +               ret = x509_validate_trust(cert, get_system_trusted_keyring());
> >> +               if (!ret)
> >> +                       prep->trusted = 1;
> 
> Actually this can be like this
> 
> >> +       } else if (!prep->trusted)
> >> +               ret = x509_validate_trust(cert,
> get_system_trusted_keyring());
> >> +               if (!ret)
> >> +                       prep->trusted = 1;
> 
> >>         }

Fine

Mimi

> >>         /* Propose a description */
> >> diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> >> index 8dabc39..72665eb 100644
> >> --- a/include/keys/system_keyring.h
> >> +++ b/include/keys/system_keyring.h
> >> @@ -17,7 +17,15 @@
> >>  #include <linux/key.h>
> >>
> >>  extern struct key *system_trusted_keyring;
> >> -
> >> +static inline struct key *get_system_trusted_keyring(void)
> >> +{
> >> +       return system_trusted_keyring;
> >> +}
> >> +#else
> >> +static inline struct key *get_system_trusted_keyring(void)
> >> +{
> >> +       return NULL;
> >> +}
> >>  #endif
> >>
> >>  #endif /* _KEYS_SYSTEM_KEYRING_H */
> >> --
> >> 1.8.1.4
> >>
> >> --
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> >
> >
> 
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> 


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