From: Vivek Goyal Subject: Re: [RFC 1/1] ima: digital signature verification using asymmetric keys Date: Fri, 25 Jan 2013 16:01:57 -0500 Message-ID: <20130125210157.GA13152@redhat.com> References: <53febcf9f13e59a1ddd8f8c9826cadbe663f2295.1358246017.git.dmitry.kasatkin@intel.com> <1358895228.2408.14.camel@falcor1> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mimi Zohar , dhowells@redhat.com, jmorris@namei.org, linux-security-module@vger.kernel.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: "Kasatkin, Dmitry" Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-security-module-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org Hi, I am trying to read and understand IMA code. How does digital signature mechanism work. IIUC, evmctl will install a file's signature in security.ima. And later process_measurement() will do following. Calculate digest of file in ima_collect_measurement() and then ima_appraise_measurement() actually compares signatuer against the digest. If yes, ima_collect_measurement() always calculates digest either using md5/sha1 but signatures might have used sha256 or something else. So how does it work. What am I missing. Thanks Vivek On Wed, Jan 23, 2013 at 11:03:39AM +0200, Kasatkin, Dmitry wrote: > On Wed, Jan 23, 2013 at 12:53 AM, Mimi Zohar wrote: > > On Tue, 2013-01-15 at 12:34 +0200, Dmitry Kasatkin wrote: > >> Asymmetric keys were introduced in linux-3.7 to verify the signature on > >> signed kernel modules. The asymmetric keys infrastructure abstracts the > >> signature verification from the crypto details. This patch adds IMA/EVM > >> signature verification using asymmetric keys. Support for additional > >> signature verification methods can now be delegated to the asymmetric > >> key infrastructure. > >> > >> Signed-off-by: Dmitry Kasatkin > >> --- > >> security/integrity/Kconfig | 12 +++++ > >> security/integrity/digsig.c | 103 ++++++++++++++++++++++++++++++++++++++++++- > >> 2 files changed, 114 insertions(+), 1 deletion(-) > >> > >> diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig > >> index 5bd1cc1..19c4187 100644 > >> --- a/security/integrity/Kconfig > >> +++ b/security/integrity/Kconfig > >> @@ -17,5 +17,17 @@ config INTEGRITY_SIGNATURE > >> This is useful for evm and module keyrings, when keys are > >> usually only added from initramfs. > >> > >> +config INTEGRITY_ASYMMETRIC_KEYS > >> + boolean "Digital signature verification using asymmetric keys" > >> + depends on INTEGRITY_SIGNATURE > >> + default n > >> + select ASYMMETRIC_KEY_TYPE > >> + select ASYMMETRIC_PUBLIC_KEY_SUBTYPE > >> + select PUBLIC_KEY_ALGO_RSA > >> + select X509_CERTIFICATE_PARSER > >> + help > >> + This option enables digital signature verification support > >> + using asymmetric keys. > >> + > >> source security/integrity/ima/Kconfig > >> source security/integrity/evm/Kconfig > >> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c > >> index 2dc167d..1896537 100644 > >> --- a/security/integrity/digsig.c > >> +++ b/security/integrity/digsig.c > >> @@ -15,10 +15,22 @@ > >> #include > >> #include > >> #include > >> +#include > >> +#include > >> #include > >> > >> #include "integrity.h" > >> > >> +/* > >> + * signature format v2 - for using with asymmetric keys > >> + */ > >> +struct signature_v2_hdr { > >> + uint8_t version; /* signature format version */ > >> + uint8_t hash_algo; /* Digest algorithm [enum pkey_hash_algo] */ > >> + uint8_t keyid[8]; /* IMA key identifier - not X509/PGP specific*/ > >> + uint8_t payload[0]; /* signature payload */ > >> +} __packed; > >> + > >> static struct key *keyring[INTEGRITY_KEYRING_MAX]; > >> > >> static const char *keyring_name[INTEGRITY_KEYRING_MAX] = { > >> @@ -27,6 +39,91 @@ static const char *keyring_name[INTEGRITY_KEYRING_MAX] = { > >> "_ima", > >> }; > >> > >> +#ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS > >> + > >> +/* > >> + * Request an asymmetric key. > >> + */ > >> +static struct key *request_asymmetric_key(struct key *keyring, uint8_t *keyid) > >> +{ > >> + struct key *key; > >> + char name[20]; > >> + > >> + sprintf(name, "%llX", __be64_to_cpup((uint64_t *)keyid)); > >> + > >> + pr_debug("key search: \"%s\"\n", name); > >> + > >> + if (keyring) { > >> + /* search in specific keyring */ > >> + key_ref_t kref; > >> + kref = keyring_search(make_key_ref(keyring, 1), > >> + &key_type_asymmetric, name); > >> + if (IS_ERR(kref)) > >> + key = ERR_CAST(kref); > >> + else > >> + key = key_ref_to_ptr(kref); > >> + } else { > >> + key = request_key(&key_type_asymmetric, name, NULL); > >> + } > >> + > >> + if (IS_ERR(key)) { > >> + pr_warn("Request for unknown key '%s' err %ld\n", > >> + name, PTR_ERR(key)); > >> + switch (PTR_ERR(key)) { > >> + /* Hide some search errors */ > >> + case -EACCES: > >> + case -ENOTDIR: > >> + case -EAGAIN: > >> + return ERR_PTR(-ENOKEY); > >> + default: > >> + return key; > >> + } > >> + } > >> + > >> + pr_debug("%s() = 0 [%x]\n", __func__, key_serial(key)); > >> + > >> + return key; > >> +} > >> + > >> +static int asymmetric_verify(struct key *keyring, const char *sig, > >> + size_t siglen, const char *data, int datalen) > >> +{ > >> + struct public_key_signature pks; > >> + struct signature_v2_hdr *hdr = (struct signature_v2_hdr *)sig; > >> + struct key *key; > >> + int ret = -ENOMEM; > >> + > >> + if (siglen <= sizeof(*hdr)) > >> + return -EBADMSG; > >> + > >> + siglen -= sizeof(*hdr); > >> + > >> + if (hdr->hash_algo >= PKEY_HASH__LAST) > >> + return -ENOPKG; > >> + > >> + key = request_asymmetric_key(keyring, hdr->keyid); > >> + if (IS_ERR(key)) > >> + return PTR_ERR(key); > >> + > >> + memset(&pks, 0, sizeof(pks)); > >> + > >> + pks.pkey_hash_algo = hdr->hash_algo; > >> + pks.digest = (u8 *)data; > >> + pks.digest_size = datalen; > >> + pks.nr_mpi = 1; > >> + pks.rsa.s = mpi_read_from_buffer(hdr->payload, &siglen); > >> + > >> + if (pks.rsa.s) > >> + ret = verify_signature(key, &pks); > >> + > >> + mpi_free(pks.rsa.s); > >> + key_put(key); > >> + pr_debug("%s() = %d\n", __func__, ret); > >> + return ret; > >> +} > >> + > >> +#endif /* CONFIG_INTEGRITY_ASYMMETRIC_KEYS */ > >> + > >> int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen, > >> const char *digest, int digestlen) > >> { > >> @@ -43,6 +140,10 @@ int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen, > >> return err; > >> } > >> } > >> - > >> +#ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS > >> + if (sig[0] == 2) > >> + return asymmetric_verify(keyring[id], sig, siglen, > >> + digest, digestlen); > >> +#endif > >> return digsig_verify(keyring[id], sig, siglen, digest, digestlen); > >> } > > > > Thanks Dmitry for the patch! According to > > Documentation/SubmittingPatches: section 2.2, #ifdefs are ugly. I > > realize this is a really small '.c' file, and doesn't really hurt > > readability, but could you remove the ifdefs anyway? > > > > Will do it. > > - Dmitry > > > thanks, > > > > Mimi > > > > > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html