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Subject[PATCHv2] added ima hook for buffer, being enabled as a policy
Date
From: Prakhar Srivastava <prsriva02@gmail.com>

Signed-off-by: Prakhar Srivastava <prsriva@microsoft.com>
---

This adds a new ima hook ima_buffer_check and a policy entry BUFFER_CHECK.
This enables buffer has measurements into ima log

Documentation/ABI/testing/ima_policy | 1 +
include/linux/ima.h | 13 +++-
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_main.c | 95 ++++++++++++++++++++++++++++
security/integrity/ima/ima_policy.c | 14 +++-
5 files changed, 122 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index bb0f9a135e21..676088c7ab26 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -28,6 +28,7 @@ Description:
base: func:= [BPRM_CHECK][MMAP_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
+ [BUFFER_CHECK]
mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
[[^]MAY_EXEC]
fsmagic:= hex value
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 7f6952f8d6aa..733d0cb9dedc 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -14,6 +14,12 @@
#include <linux/kexec.h>
struct linux_binprm;

+enum __buffer_id {
+ KERNEL_VERSION,
+ KEXEC_CMDLINE,
+ MAX_BUFFER_ID = KEXEC_CMDLINE
+} buffer_id;
+
#ifdef CONFIG_IMA
extern int ima_bprm_check(struct linux_binprm *bprm);
extern int ima_file_check(struct file *file, int mask, int opened);
@@ -23,7 +29,7 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
enum kernel_read_file_id id);
extern void ima_post_path_mknod(struct dentry *dentry);
-
+extern void ima_buffer_check(const void *buff, int size, enum buffer_id id);
#ifdef CONFIG_IMA_KEXEC
extern void ima_add_kexec_buffer(struct kimage *image);
#endif
@@ -65,6 +71,11 @@ static inline void ima_post_path_mknod(struct dentry *dentry)
return;
}

+static inline void ima_buffer_check(const void *buff, int size,
+ enum buffer_id id)
+{
+ return;
+}
#endif /* CONFIG_IMA */

#ifndef CONFIG_IMA_KEXEC
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index b563fbd4d122..b71f2f6f7421 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -181,6 +181,7 @@ enum ima_hooks {
FIRMWARE_CHECK,
KEXEC_KERNEL_CHECK,
KEXEC_INITRAMFS_CHECK,
+ BUFFER_CHECK,
POLICY_CHECK,
MAX_CHECK
};
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 2aebb7984437..6408cadaadbb 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -155,6 +155,84 @@ void ima_file_free(struct file *file)
ima_check_last_writer(iint, inode, file);
}

+/*
+ * process_buffer_measurement - Measure the buffer passed to ima log.
+ * (Instead of using the file hash the buffer hash is used).
+ * @buff - The buffer that needs to be added to the log
+ * @size - size of buffer(in bytes)
+ * @id - buffer id, this is differentiator for the various buffers
+ * that can be measured.
+ *
+ * The buffer passed is added to the ima logs.
+ * If the sig template is used, then the sig field contains the buffer.
+ *
+ * On success return 0.
+ * On error cases surface errors from ima calls.
+ */
+static int process_buffer_measurement(const void *buff, int size,
+ enum buffer_id id)
+{
+ int ret = -EINVAL;
+ struct ima_template_entry *entry = NULL;
+ struct integrity_iint_cache tmp_iint, *iint = &tmp_iint;
+ struct ima_event_data event_data = {iint, NULL, NULL,
+ NULL, 0, NULL};
+ struct {
+ struct ima_digest_data hdr;
+ char digest[IMA_MAX_DIGEST_SIZE];
+ } hash;
+ char *name = NULL;
+ int violation = 0;
+ int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
+
+ if (!buff || size == 0)
+ goto err_out;
+
+ if (ima_get_action(NULL, 0, BUFFER_CHECK, &pcr) != IMA_MEASURE)
+ goto err_out;
+
+ switch (buffer_id) {
+ case KERNEL_VERSION:
+ name = "Kernel-version";
+ break;
+ case KEXEC_CMDLINE:
+ name = "Kexec-cmdline";
+ break;
+ default:
+ goto err_out;
+ }
+
+ memset(iint, 0, sizeof(*iint));
+ memset(&hash, 0, sizeof(hash));
+
+ event_data.filename = name;
+
+ iint->ima_hash = &hash.hdr;
+ iint->ima_hash->algo = ima_hash_algo;
+ iint->ima_hash->length = hash_digest_size[ima_hash_algo];
+
+ ret = ima_calc_buffer_hash(buff, size, iint->ima_hash);
+ if (ret < 0)
+ goto err_out;
+
+ ret = ima_alloc_init_template(&event_data, &entry);
+ if (ret < 0)
+ goto err_out;
+
+ ret = ima_store_template(entry, violation, NULL,
+ buff, pcr);
+ if (ret < 0) {
+ ima_free_template_entry(entry);
+ goto err_out;
+ }
+
+ return 0;
+
+err_out:
+ pr_err("Error in adding buffer measure: %d\n", ret);
+ return ret;
+}
+
static int process_measurement(struct file *file, char *buf, loff_t size,
int mask, enum ima_hooks func, int opened)
{
@@ -370,6 +448,23 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
return 0;
}

+/**
+ * ima_buffer_check - based on policy, collect & store buffer measurement
+ * @buf: pointer to buffer
+ * @size: size of buffer
+ * @buffer_id: caller identifier
+ *
+ * Buffers can only be measured, not appraised. The buffer identifier
+ * is used as the measurement list entry name (eg. boot_cmdline).
+ */
+void ima_buffer_check(const void *buf, int size, enum buffer_id id)
+{
+ if (buf && size != 0)
+ process_buffer_measurement(buf, size, id);
+
+ return;
+}
+
static int read_idmap[READING_MAX_ID] = {
[READING_FIRMWARE] = FIRMWARE_CHECK,
[READING_MODULE] = MODULE_CHECK,
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 3ab1067db624..cefe1a188f31 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -231,6 +231,12 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
const struct cred *cred = current_cred();
int i;

+ // Incase of BUFFER_CHECK, Inode is NULL
+ if (!inode) {
+ if ((rule->flags & IMA_FUNC) && (rule->func == func))
+ return true;
+ return false;
+ }
if ((rule->flags & IMA_FUNC) &&
(rule->func != func && func != POST_SETATTR))
return false;
@@ -665,6 +671,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
else if (strcmp(args[0].from, "KEXEC_INITRAMFS_CHECK")
== 0)
entry->func = KEXEC_INITRAMFS_CHECK;
+ else if (strcmp(args[0].from, "BUFFER_CHECK") == 0)
+ entry->func = BUFFER_CHECK;
else if (strcmp(args[0].from, "POLICY_CHECK") == 0)
entry->func = POLICY_CHECK;
else
@@ -944,7 +952,7 @@ enum {
func_file = 0, func_mmap, func_bprm,
func_module, func_firmware, func_post,
func_kexec_kernel, func_kexec_initramfs,
- func_policy
+ func_buffer, func_policy
};

static char *func_tokens[] = {
@@ -956,6 +964,7 @@ static char *func_tokens[] = {
"POST_SETATTR",
"KEXEC_KERNEL_CHECK",
"KEXEC_INITRAMFS_CHECK",
+ "BUFFER_CHECK",
"POLICY_CHECK"
};

@@ -1027,6 +1036,9 @@ static void policy_func_show(struct seq_file *m, enum ima_hooks func)
case KEXEC_INITRAMFS_CHECK:
seq_printf(m, pt(Opt_func), ft(func_kexec_initramfs));
break;
+ case BUFFER_CHECK:
+ seq_printf(m, pt(Opt_func), ft(func_buffer));
+ break;
case POLICY_CHECK:
seq_printf(m, pt(Opt_func), ft(func_policy));
break;
--
2.17.1
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