Define new "d-sig" template field which holds the digest that is expected
to match the one contained in the modsig.
Suggested-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
---
Documentation/security/IMA-templates.rst | 5 ++++
security/integrity/ima/ima.h | 9 +++++++
security/integrity/ima/ima_modsig.c | 23 ++++++++++++++++
security/integrity/ima/ima_template.c | 4 ++-
security/integrity/ima/ima_template_lib.c | 32 ++++++++++++++++++++++-
security/integrity/ima/ima_template_lib.h | 2 ++
6 files changed, 73 insertions(+), 2 deletions(-)
diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index 2cd0e273cc9a..f2a0f4225857 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -68,6 +68,11 @@ descriptors by adding their identifier to the format string
- 'd-ng': the digest of the event, calculated with an arbitrary hash
algorithm (field format: [<hash algo>:]digest, where the digest
prefix is shown only if the hash algorithm is not SHA1 or MD5);
+ - 'd-sig': the digest of the event for files that have an appended modsig. This
+ field is calculated without including the modsig and thus will differ from
+ the total digest of the file, but it is what should match the digest
+ contained in the modsig (if it doesn't, the signature is invalid). It is
+ shown in the same format as 'd-ng';
- 'n-ng': the name of the event, without size limitations;
- 'sig': the file signature.
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 753d59352718..40a6ddfdd9ea 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -316,6 +316,8 @@ int ima_read_collect_modsig(enum ima_hooks func, const void *buf,
loff_t buf_len,
struct evm_ima_xattr_data **xattr_value,
int *xattr_len);
+int ima_get_modsig_hash(struct evm_ima_xattr_data *hdr, enum hash_algo *algo,
+ const u8 **hash, u8 *len);
void ima_free_xattr_data(struct evm_ima_xattr_data *hdr);
#else
static inline bool ima_hook_supports_modsig(enum ima_hooks func)
@@ -331,6 +333,13 @@ static inline int ima_read_collect_modsig(enum ima_hooks func, const void *buf,
return -EOPNOTSUPP;
}
+static inline int ima_get_modsig_hash(struct evm_ima_xattr_data *hdr,
+ enum hash_algo *algo, const u8 **hash,
+ u8 *len)
+{
+ return -EOPNOTSUPP;
+}
+
static inline void ima_free_xattr_data(struct evm_ima_xattr_data *hdr)
{
kfree(hdr);
diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index f228f333509d..587b79a9afef 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -167,6 +167,29 @@ int ima_read_collect_modsig(enum ima_hooks func, const void *buf,
return rc;
}
+int ima_get_modsig_hash(struct evm_ima_xattr_data *hdr, enum hash_algo *algo,
+ const u8 **hash, u8 *len)
+{
+ struct modsig_hdr *modsig = (typeof(modsig)) hdr;
+ const struct public_key_signature *pks;
+ int i;
+
+ if (!hdr || hdr->type != IMA_MODSIG)
+ return -EINVAL;
+
+ pks = pkcs7_get_message_sig(modsig->pkcs7_msg);
+ if (!pks)
+ return -EBADMSG;
+
+ for (i = 0; i < HASH_ALGO__LAST; i++)
+ if (!strcmp(hash_algo_name[i], pks->hash_algo))
+ break;
+
+ *algo = i;
+
+ return pkcs7_get_digest(modsig->pkcs7_msg, hash, len);
+}
+
int ima_modsig_verify(struct key *keyring, const void *hdr)
{
const struct modsig_hdr *modsig = (const struct modsig_hdr *) hdr;
diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index b631b8bc7624..045ad508cbb8 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -43,8 +43,10 @@ static const struct ima_template_field supported_fields[] = {
.field_show = ima_show_template_string},
{.field_id = "sig", .field_init = ima_eventsig_init,
.field_show = ima_show_template_sig},
+ {.field_id = "d-sig", .field_init = ima_eventdigest_sig_init,
+ .field_show = ima_show_template_digest_ng},
};
-#define MAX_TEMPLATE_NAME_LEN 15
+#define MAX_TEMPLATE_NAME_LEN 24
static struct ima_template_desc *ima_template;
static struct ima_template_desc *lookup_template_desc(const char *name);
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index 300912914b17..36d175816894 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -222,7 +222,8 @@ int ima_parse_buf(void *bufstartp, void *bufendp, void **bufcurp,
return 0;
}
-static int ima_eventdigest_init_common(u8 *digest, u32 digestsize, u8 hash_algo,
+static int ima_eventdigest_init_common(const u8 *digest, u32 digestsize,
+ u8 hash_algo,
struct ima_field_data *field_data)
{
/*
@@ -325,6 +326,35 @@ int ima_eventdigest_ng_init(struct ima_event_data *event_data,
hash_algo, field_data);
}
+/*
+ * This function writes the digest of the file which is expected to match the
+ * digest contained in the file's embedded signature.
+ */
+int ima_eventdigest_sig_init(struct ima_event_data *event_data,
+ struct ima_field_data *field_data)
+{
+ struct evm_ima_xattr_data *xattr_value = event_data->xattr_value;
+ enum hash_algo hash_algo = HASH_ALGO_SHA1;
+ const u8 *cur_digest = NULL;
+ u8 cur_digestsize = 0;
+ int ret;
+
+ if (!xattr_value || xattr_value->type != IMA_MODSIG)
+ return 0;
+
+ if (event_data->violation) /* recording a violation. */
+ goto out;
+
+ ret = ima_get_modsig_hash(xattr_value, &hash_algo, &cur_digest,
+ &cur_digestsize);
+ if (ret)
+ return ret;
+
+ out:
+ return ima_eventdigest_init_common(cur_digest, cur_digestsize,
+ hash_algo, field_data);
+}
+
static int ima_eventname_init_common(struct ima_event_data *event_data,
struct ima_field_data *field_data,
bool size_limit)
diff --git a/security/integrity/ima/ima_template_lib.h b/security/integrity/ima/ima_template_lib.h
index 6a3d8b831deb..3cd353e83f73 100644
--- a/security/integrity/ima/ima_template_lib.h
+++ b/security/integrity/ima/ima_template_lib.h
@@ -38,6 +38,8 @@ int ima_eventname_init(struct ima_event_data *event_data,
struct ima_field_data *field_data);
int ima_eventdigest_ng_init(struct ima_event_data *event_data,
struct ima_field_data *field_data);
+int ima_eventdigest_sig_init(struct ima_event_data *event_data,
+ struct ima_field_data *field_data);
int ima_eventname_ng_init(struct ima_event_data *event_data,
struct ima_field_data *field_data);
int ima_eventsig_init(struct ima_event_data *event_data,
