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From:   Prakhar Srivastava <prsriva02@gmail.com>
To:     linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     zohar@linux.vnet.ibm.com, Prakhar Srivastava <prsriva02@gmail.com>,
        Prakhar Srivastava <prsriva@microsoft.com>
Subject: [PATCHv2] added ima hook for buffer, being enabled as a policy
Date:   Fri, 19 Apr 2019 17:00:55 -0700
Message-Id: <20190420000057.5222-1-prsriva02@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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