[PATCH v6 7/9] ima: check against blacklisted hashes for files with modsig

Nayna Jain
2019-09-27T14:27:14Z

Asymmetric private keys are used to sign multiple files. The kernel
currently support checking against the blacklisted keys. However, if the
public key is blacklisted, any file signed by the blacklisted key will
automatically fail signature verification. We might not want to blacklist
all the files signed by a particular key, but just a single file.
Blacklisting the public key is not fine enough granularity.

This patch adds support for blacklisting binaries with appended signatures,
based on the IMA policy. Defined is a new policy option
"appraise_flag=check_blacklist".

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
---
Documentation/ABI/testing/ima_policy | 1 +
security/integrity/ima/ima.h | 12 +++++++++
security/integrity/ima/ima_appraise.c | 35 +++++++++++++++++++++++++++
security/integrity/ima/ima_main.c | 8 ++++--
security/integrity/ima/ima_policy.c | 10 ++++++--
security/integrity/integrity.h | 1 +
6 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 29ebe9afdac4..4c97afcc0f3c 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -25,6 +25,7 @@ Description:
lsm: [[subj_user=] [subj_role=] [subj_type=]
[obj_user=] [obj_role=] [obj_type=]]
option: [[appraise_type=]] [template=] [permit_directio]
+ [appraise_flag=[check_blacklist]]
base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 9bf509217e8e..2c034728b239 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -254,6 +254,9 @@ int ima_policy_show(struct seq_file *m, void *v);
#define IMA_APPRAISE_KEXEC 0x40

#ifdef CONFIG_IMA_APPRAISE
+int ima_blacklist_measurement(struct integrity_iint_cache *iint,
+ const struct modsig *modsig, int action,
+ int pcr, struct ima_template_desc *template_desc);
int ima_appraise_measurement(enum ima_hooks func,
struct integrity_iint_cache *iint,
struct file *file, const unsigned char *filename,
@@ -269,6 +272,15 @@ int ima_read_xattr(struct dentry *dentry,
struct evm_ima_xattr_data **xattr_value);

#else
+static inline int ima_blacklist_measurement(struct integrity_iint_cache *iint,
+ const struct modsig *modsig,
+ int action, int pcr,
+ struct ima_template_desc
+ *template_desc)
+{
+ return 0;
+}
+
static inline int ima_appraise_measurement(enum ima_hooks func,
struct integrity_iint_cache *iint,
struct file *file,
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 136ae4e0ee92..a5a82e870e24 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -12,6 +12,7 @@
#include <linux/magic.h>
#include <linux/ima.h>
#include <linux/evm.h>
+#include <keys/system_keyring.h>

#include "ima.h"

@@ -303,6 +304,40 @@ static int modsig_verify(enum ima_hooks func, const struct modsig *modsig,
return rc;
}

+/*
+ * ima_blacklist_measurement - checks if the file measurement is blacklisted
+ *
+ * Returns -EKEYREJECTED if the hash is blacklisted.
+ */
+int ima_blacklist_measurement(struct integrity_iint_cache *iint,
+ const struct modsig *modsig, int action, int pcr,
+ struct ima_template_desc *template_desc)
+{
+ enum hash_algo hash_algo;
+ const u8 *digest = NULL;
+ u32 digestsize = 0;
+ u32 secid;
+ int rc = 0;
+
+ if (!(iint->flags & IMA_CHECK_BLACKLIST))
+ return 0;
+
+ if (iint->flags & IMA_MODSIG_ALLOWED) {
+ security_task_getsecid(current, &secid);
+ ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
+
+ rc = is_hash_blacklisted(digest, digestsize, "bin");
+
+ /* Returns -EKEYREJECTED on blacklisted hash found */
+ if ((rc == -EKEYREJECTED) && (iint->flags & IMA_MEASURE))
+ process_buffer_measurement(digest, digestsize,
+ "blacklisted-hash", pcr,
+ template_desc);
+ }
+
+ return rc;
+}
+
/*
* ima_appraise_measurement - appraise file measurement
*
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index ae0c1bdc4eaf..92c446045637 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -336,8 +336,12 @@ static int process_measurement(struct file *file, const struct cred *cred,
template_desc);
if (rc == 0 && (action & IMA_APPRAISE_SUBMASK)) {
inode_lock(inode);
- rc = ima_appraise_measurement(func, iint, file, pathname,
- xattr_value, xattr_len, modsig);
+ rc = ima_blacklist_measurement(iint, modsig, action, pcr,
+ template_desc);
+ if (rc != -EKEYREJECTED)
+ rc = ima_appraise_measurement(func, iint, file,
+ pathname, xattr_value,
+ xattr_len, modsig);
inode_unlock(inode);
if (!rc)
rc = mmap_violation_check(func, file, &pathbuf,
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 4badc4fcda98..ad3b3af69460 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -765,8 +765,8 @@ enum {
Opt_fsuuid, Opt_uid_eq, Opt_euid_eq, Opt_fowner_eq,
Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt,
Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
- Opt_appraise_type, Opt_permit_directio,
- Opt_pcr, Opt_template, Opt_err
+ Opt_appraise_type, Opt_appraise_flag,
+ Opt_permit_directio, Opt_pcr, Opt_template, Opt_err
};

static const match_table_t policy_tokens = {
@@ -798,6 +798,7 @@ static const match_table_t policy_tokens = {
{Opt_euid_lt, "euid<%s"},
{Opt_fowner_lt, "fowner<%s"},
{Opt_appraise_type, "appraise_type=%s"},
+ {Opt_appraise_flag, "appraise_flag=%s"},
{Opt_permit_directio, "permit_directio"},
{Opt_pcr, "pcr=%s"},
{Opt_template, "template=%s"},
@@ -1172,6 +1173,11 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
else
result = -EINVAL;
break;
+ case Opt_appraise_flag:
+ ima_log_string(ab, "appraise_flag", args[0].from);
+ if (strstr(args[0].from, "blacklist"))
+ entry->flags |= IMA_CHECK_BLACKLIST;
+ break;
case Opt_permit_directio:
entry->flags |= IMA_PERMIT_DIRECTIO;
break;
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index d9323d31a3a8..73fc286834d7 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -32,6 +32,7 @@
#define EVM_IMMUTABLE_DIGSIG 0x08000000
#define IMA_FAIL_UNVERIFIABLE_SIGS 0x10000000
#define IMA_MODSIG_ALLOWED 0x20000000
+#define IMA_CHECK_BLACKLIST 0x40000000

#define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
IMA_HASH | IMA_APPRAISE_SUBMASK)
--
2.20.1