[PATCH v12 09/11] ima: Define ima-modsig template

Thiago Jung Bauermann
2019-06-28T02:20:57Z

Define new "d-modsig" template field which holds the digest that is
expected to match the one contained in the modsig, and also new "modsig"
template field which holds the appended file signature.

Add a new "ima-modsig" defined template descriptor with the new fields as
well as the ones from the "ima-sig" descriptor.

Change ima_store_measurement() to accept a struct modsig * argument so that
it can be passed along to the templates via struct ima_event_data.

Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
Documentation/security/IMA-templates.rst | 3 ++
security/integrity/ima/ima.h | 20 ++++++-
security/integrity/ima/ima_api.c | 5 +-
security/integrity/ima/ima_main.c | 2 +-
security/integrity/ima/ima_modsig.c | 19 +++++++
security/integrity/ima/ima_policy.c | 41 +++++++++++++++
security/integrity/ima/ima_template.c | 7 ++-
security/integrity/ima/ima_template_lib.c | 64 ++++++++++++++++++++++-
security/integrity/ima/ima_template_lib.h | 4 ++
9 files changed, 159 insertions(+), 6 deletions(-)

diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index 3d1cca287aa4..c5a8432972ef 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -68,8 +68,10 @@ 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-modsig': the digest of the event without the appended modsig;
- 'n-ng': the name of the event, without size limitations;
- 'sig': the file signature;
+ - 'modsig' the appended file signature;
- 'buf': the buffer data that was used to generate the hash without size limitations;

@@ -79,6 +81,7 @@ Below, there is the list of defined template descriptors:
- "ima-ng" (default): its format is ``d-ng|n-ng``;
- "ima-sig": its format is ``d-ng|n-ng|sig``;
- "ima-buf": its format is ``d-ng|n-ng|buf``;
+ - "ima-modsig": its format is ``d-ng|n-ng|sig|d-modsig|modsig``;

Use
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index baf2ffd52a41..3293dd07b6c9 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -64,6 +64,7 @@ struct ima_event_data {
const unsigned char *filename;
struct evm_ima_xattr_data *xattr_value;
int xattr_len;
+ const struct modsig *modsig;
const char *violation;
const void *buf;
int buf_len;
@@ -215,7 +216,7 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
void ima_store_measurement(struct integrity_iint_cache *iint, struct file *file,
const unsigned char *filename,
struct evm_ima_xattr_data *xattr_value,
- int xattr_len, int pcr,
+ int xattr_len, const struct modsig *modsig, int pcr,
struct ima_template_desc *template_desc);
void ima_audit_measurement(struct integrity_iint_cache *iint,
const unsigned char *filename);
@@ -316,6 +317,10 @@ bool ima_hook_supports_modsig(enum ima_hooks func);
int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
struct modsig **modsig);
void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size);
+int ima_get_modsig_digest(const struct modsig *modsig, enum hash_algo *algo,
+ const u8 **digest, u32 *digest_size);
+int ima_get_raw_modsig(const struct modsig *modsig, const void **data,
+ u32 *data_len);
void ima_free_modsig(struct modsig *modsig);
#else
static inline bool ima_hook_supports_modsig(enum ima_hooks func)
@@ -334,6 +339,19 @@ static inline void ima_collect_modsig(struct modsig *modsig, const void *buf,
{
}

+static inline int ima_get_modsig_digest(const struct modsig *modsig,
+ enum hash_algo *algo, const u8 **digest,
+ u32 *digest_size)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline int ima_get_raw_modsig(const struct modsig *modsig,
+ const void **data, u32 *data_len)
+{
+ return -EOPNOTSUPP;
+}
+
static inline void ima_free_modsig(struct modsig *modsig)
{
}
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index ac35bc3d6e35..9d1fe712a6cc 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -292,7 +292,7 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
void ima_store_measurement(struct integrity_iint_cache *iint,
struct file *file, const unsigned char *filename,
struct evm_ima_xattr_data *xattr_value,
- int xattr_len, int pcr,
+ int xattr_len, const struct modsig *modsig, int pcr,
struct ima_template_desc *template_desc)
{
static const char op[] = "add_template_measure";
@@ -304,7 +304,8 @@ void ima_store_measurement(struct integrity_iint_cache *iint,
.file = file,
.filename = filename,
.xattr_value = xattr_value,
- .xattr_len = xattr_len };
+ .xattr_len = xattr_len,
+ .modsig = modsig };
int violation = 0;

if (iint->measured_pcrs & (0x1 << pcr))
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index cc4500f93408..8b35a200e0cc 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -327,7 +327,7 @@ static int process_measurement(struct file *file, const struct cred *cred,

if (action & IMA_MEASURE)
ima_store_measurement(iint, file, pathname,
- xattr_value, xattr_len, pcr,
+ xattr_value, xattr_len, modsig, pcr,
template_desc);
if (rc == 0 && (action & IMA_APPRAISE_SUBMASK)) {
inode_lock(inode);
diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index d438b87dba89..b01bbfeb1d98 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -140,6 +140,25 @@ int ima_modsig_verify(struct key *keyring, const struct modsig *modsig)
VERIFYING_MODULE_SIGNATURE, NULL, NULL);
}

+int ima_get_modsig_digest(const struct modsig *modsig, enum hash_algo *algo,
+ const u8 **digest, u32 *digest_size)
+{
+ *algo = modsig->hash_algo;
+ *digest = modsig->digest;
+ *digest_size = modsig->digest_size;
+
+ return 0;
+}
+
+int ima_get_raw_modsig(const struct modsig *modsig, const void **data,
+ u32 *data_len)
+{
+ *data = &modsig->raw_pkcs7;
+ *data_len = modsig->raw_pkcs7_len;
+
+ return 0;
+}
+
void ima_free_modsig(struct modsig *modsig)
{
if (!modsig)
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 4c5b968c4721..4fc13e591f1d 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -10,6 +10,9 @@
* - initialize default measure policy rules
*
*/
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
#include <linux/init.h>
#include <linux/list.h>
#include <linux/fs.h>
@@ -847,6 +850,38 @@ static void ima_log_string(struct audit_buffer *ab, char *key, char *value)
ima_log_string_op(ab, key, value, NULL);
}

+/*
+ * Validating the appended signature included in the measurement list requires
+ * the file hash calculated without the appended signature (i.e., the 'd-modsig'
+ * field). Therefore, notify the user if they have the 'modsig' field but not
+ * the 'd-modsig' field in the template.
+ */
+static void check_template_modsig(const struct ima_template_desc *template)
+{
+#define MSG "template with 'modsig' field also needs 'd-modsig' field\n"
+ bool has_modsig, has_dmodsig;
+ static bool checked;
+ int i;
+
+ /* We only need to notify the user once. */
+ if (checked)
+ return;
+
+ has_modsig = has_dmodsig = false;
+ for (i = 0; i < template->num_fields; i++) {
+ if (!strcmp(template->fields[i]->field_id, "modsig"))
+ has_modsig = true;
+ else if (!strcmp(template->fields[i]->field_id, "d-modsig"))
+ has_dmodsig = true;
+ }
+
+ if (has_modsig && !has_dmodsig)
+ pr_notice(MSG);
+
+ checked = true;
+#undef MSG
+}
+
static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
{
struct audit_buffer *ab;
@@ -1189,6 +1224,12 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
else if (entry->action == APPRAISE)
temp_ima_appraise |= ima_appraise_flag(entry->func);

+ if (!result && entry->flags & IMA_MODSIG_ALLOWED) {
+ template_desc = entry->template ? entry->template :
+ ima_template_desc_current();
+ check_template_modsig(template_desc);
+ }
+
audit_log_format(ab, "res=%d", !result);
audit_log_end(ab);
return result;
diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index 7343e8e0ae2f..ac526b34973f 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -27,6 +27,7 @@ static struct ima_template_desc builtin_templates[] = {
{.name = "ima-ng", .fmt = "d-ng|n-ng"},
{.name = "ima-sig", .fmt = "d-ng|n-ng|sig"},
{.name = "ima-buf", .fmt = "d-ng|n-ng|buf"},
+ {.name = "ima-modsig", .fmt = "d-ng|n-ng|sig|d-modsig|modsig"},
{.name = "", .fmt = ""}, /* placeholder for a custom format */
};

@@ -46,6 +47,10 @@ static const struct ima_template_field supported_fields[] = {
.field_show = ima_show_template_sig},
{.field_id = "buf", .field_init = ima_eventbuf_init,
.field_show = ima_show_template_buf},
+ {.field_id = "d-modsig", .field_init = ima_eventdigest_modsig_init,
+ .field_show = ima_show_template_digest_ng},
+ {.field_id = "modsig", .field_init = ima_eventmodsig_init,
+ .field_show = ima_show_template_sig},
};

/*
@@ -53,7 +58,7 @@ static const struct ima_template_field supported_fields[] = {
* need to be accounted for since they shouldn't be defined in the same template
* description as 'd-ng' and 'n-ng' respectively.
*/
-#define MAX_TEMPLATE_NAME_LEN sizeof("d-ng|n-ng|sig|buf")
+#define MAX_TEMPLATE_NAME_LEN sizeof("d-ng|n-ng|sig|buf|d-modisg|modsig")

static struct ima_template_desc *ima_template;

diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index baf4de45c5aa..22e71cd5ca02 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -229,7 +229,8 @@ 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)
{
/*
@@ -332,6 +333,41 @@ 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 appended signature.
+ */
+int ima_eventdigest_modsig_init(struct ima_event_data *event_data,
+ struct ima_field_data *field_data)
+{
+ enum hash_algo hash_algo;
+ const u8 *cur_digest;
+ u32 cur_digestsize;
+
+ if (!event_data->modsig)
+ return 0;
+
+ if (event_data->violation) {
+ /* Recording a violation. */
+ hash_algo = HASH_ALGO_SHA1;
+ cur_digest = NULL;
+ cur_digestsize = 0;
+ } else {
+ int rc;
+
+ rc = ima_get_modsig_digest(event_data->modsig, &hash_algo,
+ &cur_digest, &cur_digestsize);
+ if (rc)
+ return rc;
+ else if (hash_algo == HASH_ALGO__LAST || cur_digestsize == 0)
+ /* There was some error collecting the digest. */
+ return -EINVAL;
+ }
+
+ 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)
@@ -410,3 +446,29 @@ int ima_eventbuf_init(struct ima_event_data *event_data,
event_data->buf_len, DATA_FMT_HEX,
field_data);
}
+
+/*
+ * ima_eventmodsig_init - include the appended file signature as part of the
+ * template data
+ */
+int ima_eventmodsig_init(struct ima_event_data *event_data,
+ struct ima_field_data *field_data)
+{
+ const void *data;
+ u32 data_len;
+ int rc;
+
+ if (!event_data->modsig)
+ return 0;
+
+ /*
+ * modsig is a runtime structure containing pointers. Get its raw data
+ * instead.
+ */
+ rc = ima_get_raw_modsig(event_data->modsig, &data, &data_len);
+ if (rc)
+ return rc;
+
+ return ima_write_template_field_data(data, data_len, DATA_FMT_HEX,
+ field_data);
+}
diff --git a/security/integrity/ima/ima_template_lib.h b/security/integrity/ima/ima_template_lib.h
index 12f1a8578b31..6544eac1c77d 100644
--- a/security/integrity/ima/ima_template_lib.h
+++ b/security/integrity/ima/ima_template_lib.h
@@ -40,10 +40,14 @@ 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_modsig_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,
struct ima_field_data *field_data);
int ima_eventbuf_init(struct ima_event_data *event_data,
struct ima_field_data *field_data);
+int ima_eventmodsig_init(struct ima_event_data *event_data,
+ struct ima_field_data *field_data);
#endif /* __LINUX_IMA_TEMPLATE_LIB_H */