@@ -36,7 +36,7 @@ Description:
euid:= decimal value
fowner:= decimal value
lsm: are LSM specific
- option: appraise_type:= [imasig]
+ option: appraise_type:= [imasig] [modsig|imasig]
pcr:= decimal value
default policy:
@@ -102,3 +102,7 @@ Description:
measure func=KEXEC_KERNEL_CHECK pcr=4
measure func=KEXEC_INITRAMFS_CHECK pcr=5
+
+ Example of appraise rule allowing modsig appended signatures:
+
+ appraise func=KEXEC_KERNEL_CHECK appraise_type=modsig|imasig
@@ -163,6 +163,16 @@ config IMA_APPRAISE_BOOTPARAM
This option enables the different "ima_appraise=" modes
(eg. fix, log) from the boot command line.
+config IMA_APPRAISE_MODSIG
+ bool "Support module-style signatures for appraisal"
+ depends on IMA_APPRAISE
+ default n
+ help
+ Adds support for signatures appended to files. The format of the
+ appended signature is the same used for signed kernel modules.
+ The modsig keyword can be used in the IMA policy to allow a hook
+ to accept such signatures.
+
config IMA_TRUSTED_KEYRING
bool "Require all keys on the .ima keyring be signed (deprecated)"
depends on IMA_APPRAISE && SYSTEM_TRUSTED_KEYRING
@@ -8,5 +8,6 @@ obj-$(CONFIG_IMA) += ima.o
ima-y := ima_fs.o ima_queue.o ima_init.o ima_main.o ima_crypto.o ima_api.o \
ima_policy.o ima_template.o ima_template_lib.o
ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
+ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o
ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
@@ -255,6 +255,10 @@ enum hash_algo ima_get_hash_algo(struct evm_ima_xattr_data *xattr_value,
int ima_read_xattr(struct dentry *dentry,
struct evm_ima_xattr_data **xattr_value);
+#ifdef CONFIG_IMA_APPRAISE_MODSIG
+bool ima_hook_supports_modsig(enum ima_hooks func);
+#endif
+
#else
static inline int ima_appraise_measurement(enum ima_hooks func,
struct integrity_iint_cache *iint,
@@ -298,6 +302,13 @@ static inline int ima_read_xattr(struct dentry *dentry,
#endif /* CONFIG_IMA_APPRAISE */
+#ifndef CONFIG_IMA_APPRAISE_MODSIG
+static inline bool ima_hook_supports_modsig(enum ima_hooks func)
+{
+ return false;
+}
+#endif
+
/* LSM based policy rules require audit */
#ifdef CONFIG_IMA_LSM_RULES
new file mode 100644
@@ -0,0 +1,39 @@
+/*
+ * IMA support for appraising module-style appended signatures.
+ *
+ * Copyright (C) 2017 IBM Corporation
+ *
+ * Author:
+ * Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation (version 2 of the License).
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#include "ima.h"
+
+/**
+ * ima_hook_supports_modsig - can the policy allow modsig for this hook?
+ *
+ * modsig is only supported by hooks using ima_post_read_file, because only they
+ * preload the contents of the file in a buffer. FILE_CHECK does that in some
+ * cases, but not when reached from vfs_open. POLICY_CHECK can support it, but
+ * it's not useful in practice because it's a text file so deny.
+ */
+bool ima_hook_supports_modsig(enum ima_hooks func)
+{
+ switch (func) {
+ case FIRMWARE_CHECK:
+ case KEXEC_KERNEL_CHECK:
+ case KEXEC_INITRAMFS_CHECK:
+ return true;
+ default:
+ return false;
+ }
+}
@@ -854,6 +854,10 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
ima_log_string(ab, "appraise_type", args[0].from);
if (strcmp(args[0].from, "imasig") == 0)
entry->flags |= IMA_DIGSIG_REQUIRED;
+ else if (ima_hook_supports_modsig(entry->func) &&
+ strcmp(args[0].from, "modsig|imasig") == 0)
+ entry->flags |= IMA_DIGSIG_REQUIRED
+ | IMA_MODSIG_ALLOWED;
else
result = -EINVAL;
break;
@@ -1139,8 +1143,12 @@ int ima_policy_show(struct seq_file *m, void *v)
}
}
}
- if (entry->flags & IMA_DIGSIG_REQUIRED)
- seq_puts(m, "appraise_type=imasig ");
+ if (entry->flags & IMA_DIGSIG_REQUIRED) {
+ if (entry->flags & IMA_MODSIG_ALLOWED)
+ seq_puts(m, "appraise_type=modsig|imasig ");
+ else
+ seq_puts(m, "appraise_type=imasig ");
+ }
if (entry->flags & IMA_PERMIT_DIRECTIO)
seq_puts(m, "permit_directio ");
rcu_read_unlock();
@@ -28,11 +28,12 @@
/* iint cache flags */
#define IMA_ACTION_FLAGS 0xff000000
-#define IMA_ACTION_RULE_FLAGS 0x06000000
+#define IMA_ACTION_RULE_FLAGS 0x16000000
#define IMA_DIGSIG 0x01000000
#define IMA_DIGSIG_REQUIRED 0x02000000
#define IMA_PERMIT_DIRECTIO 0x04000000
#define IMA_NEW_FILE 0x08000000
+#define IMA_MODSIG_ALLOWED 0x10000000
#define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
IMA_APPRAISE_SUBMASK)
This patch introduces the modsig keyword to the IMA policy syntax to specify that a given hook should expect the file to have the IMA signature appended to it. Here is how it can be used in a rule: appraise func=KEXEC_KERNEL_CHECK appraise_type=modsig|imasig With this rule, IMA will accept either an appended signature or a signature stored in the extended attribute. In that case, it will first check whether there is an appended signature, and if not it will read it from the extended attribute. For now, the rule above will behave exactly the same as if appraise_type=imasig was specified because the actual modsig implementation will be introduced in a separate patch. Suggested-by: Mimi Zohar <zohar@linux.vnet.ibm.com> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> --- Documentation/ABI/testing/ima_policy | 6 +++++- security/integrity/ima/Kconfig | 10 +++++++++ security/integrity/ima/Makefile | 1 + security/integrity/ima/ima.h | 11 ++++++++++ security/integrity/ima/ima_modsig.c | 39 ++++++++++++++++++++++++++++++++++++ security/integrity/ima/ima_policy.c | 12 +++++++++-- security/integrity/integrity.h | 3 ++- 7 files changed, 78 insertions(+), 4 deletions(-)