[PATCH v11 11/13] ima: Define ima-modsig template

From: Thiago Jung Bauermann
Date: Tue Jun 11 2019 - 02:35:06 EST

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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@xxxxxxxxxxxxx>
Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
Documentation/security/IMA-templates.rst | 7 ++-
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 | 60 ++++++++++++++++++++++-
security/integrity/ima/ima_template_lib.h | 4 ++
9 files changed, 157 insertions(+), 8 deletions(-)

diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index 2cd0e273cc9a..8da20b444be0 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -68,15 +68,18 @@ 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.
+ - 'sig': the file signature;
+ - 'modsig' the appended file signature.

Below, there is the list of defined template descriptors:

- "ima": its format is ``d|n``;
- "ima-ng" (default): its format is ``d-ng|n-ng``;
- - "ima-sig": its format is ``d-ng|n-ng|sig``.
+ - "ima-sig": its format is ``d-ng|n-ng|sig``;
+ - "ima-modsig": its format is ``d-ng|n-ng|sig|d-modsig|modsig``.

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 0acc8e56ec73..a2b2c13ceda8 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;
};

@@ -207,7 +208,7 @@ 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);
@@ -308,6 +309,10 @@ 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)
@@ -326,6 +331,19 @@ 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 c351b8c37278..32297d1e6164 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -291,7 +291,7 @@ 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";
@@ -303,7 +303,8 @@ 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 2c9d3cf85726..85afb31fafe0 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -323,7 +323,7 @@ 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 f64ef84516db..6463ab8921ea 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>
@@ -766,6 +769,38 @@ 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;
@@ -1096,6 +1131,12 @@ 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 e6e892f31cbd..e25bef419c87 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -26,6 +26,7 @@ static struct ima_template_desc builtin_templates[] = {
{.name = IMA_TEMPLATE_IMA_NAME, .fmt = IMA_TEMPLATE_IMA_FMT},
{.name = "ima-ng", .fmt = "d-ng|n-ng"},
{.name = "ima-sig", .fmt = "d-ng|n-ng|sig"},
+ {.name = "ima-modsig", .fmt = "d-ng|n-ng|sig|d-modsig|modsig"},
{.name = "", .fmt = ""}, /* placeholder for a custom format */
};

@@ -43,8 +44,12 @@ 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-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},
};
-#define MAX_TEMPLATE_NAME_LEN 15
+#define MAX_TEMPLATE_NAME_LEN sizeof("d|n|d-ng|n-ng|sig|d-modisg|modsig")

static struct ima_template_desc *ima_template;
static int template_desc_init_fields(const char *template_fmt,
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index 513b457ae900..dacb01fb105f 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -223,7 +223,8 @@ 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)
{
/*
@@ -326,6 +327,41 @@ 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 embedded 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)
@@ -389,3 +425,25 @@ int ima_eventsig_init(struct ima_event_data *event_data,
return ima_write_template_field_data(xattr_value, event_data->xattr_len,
DATA_FMT_HEX, field_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 6a3d8b831deb..1d7c690ebae5 100644
--- a/security/integrity/ima/ima_template_lib.h
+++ b/security/integrity/ima/ima_template_lib.h
@@ -38,8 +38,12 @@ 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_eventmodsig_init(struct ima_event_data *event_data,
+ struct ima_field_data *field_data);
#endif /* __LINUX_IMA_TEMPLATE_LIB_H */

Next message: Anson . Huang: "[PATCH 1/3] dt-bindings: fsl: scu: Update RTC compatible string"
Previous message: Thiago Jung Bauermann: "[PATCH v11 13/13] ima: Allow template= option for appraise rules as well"
In reply to: Thiago Jung Bauermann: "[PATCH v11 13/13] ima: Allow template= option for appraise rules as well"
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