[PATCH v4 2/8] ima: define ima_max_digest_data struct without a flexible array variable

[Mimi Zohar <zohar@linux.ibm.com>]

To support larger hash digests in the 'iint' cache, instead of defining
the 'digest' field as the maximum digest size, the 'digest' field was
defined as a flexible array variable and was dynamically allocated.
This resulted in wrapping the "ima_digest_data" struct inside a local
structure with the maximum digest size in a number of places.

The original reason for defining the 'digest' field as a flexible array
variable is still valid for the 'iint' cache use case.  In addition,
define 'ima_max_digest_data' struct to be use instead of the (ugly)
local wrapping of the "ima_digest_data" struct.

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/ima/ima_api.c  | 20 ++++++++++----------
 security/integrity/ima/ima_init.c | 10 ++++------
 security/integrity/integrity.h    | 24 ++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 16 deletions(-)

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 5b220a2fe573..45294f18dabc 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -217,14 +217,11 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 	const char *audit_cause = "failed";
 	struct inode *inode = file_inode(file);
 	const char *filename = file->f_path.dentry->d_name.name;
+	struct ima_max_digest_data hash;
 	int result = 0;
 	int length;
 	void *tmpbuf;
 	u64 i_version;
-	struct {
-		struct ima_digest_data hdr;
-		char digest[IMA_MAX_DIGEST_SIZE];
-	} hash;
 
 	/*
 	 * Always collect the modsig, because IMA might have already collected
@@ -239,24 +236,27 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 
 	/*
 	 * Detecting file change is based on i_version. On filesystems
-	 * which do not support i_version, support is limited to an initial
-	 * measurement/appraisal/audit.
+	 * which do not support i_version, support was originally limited
+	 * to an initial measurement/appraisal/audit, but was modified to
+	 * assume the file changed.
 	 */
 	i_version = inode_query_iversion(inode);
-	hash.hdr.algo = algo;
+	hash.algo = algo;
 
 	/* Initialize hash digest to 0's in case of failure */
 	memset(&hash.digest, 0, sizeof(hash.digest));
 
 	if (buf)
-		result = ima_calc_buffer_hash(buf, size, &hash.hdr);
+		result = ima_calc_buffer_hash(buf, size,
+					      (struct ima_digest_data *)&hash);
 	else
-		result = ima_calc_file_hash(file, &hash.hdr);
+		result = ima_calc_file_hash(file,
+					    (struct ima_digest_data *)&hash);
 
 	if (result && result != -EBADF && result != -EINVAL)
 		goto out;
 
-	length = sizeof(hash.hdr) + hash.hdr.length;
+	length = sizeof(struct ima_digest_data) + hash.length;
 	tmpbuf = krealloc(iint->ima_hash, length, GFP_NOFS);
 	if (!tmpbuf) {
 		result = -ENOMEM;
diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index b26fa67476b4..890821af08dd 100644
--- a/security/integrity/ima/ima_init.c
+++ b/security/integrity/ima/ima_init.c
@@ -47,16 +47,13 @@ static int __init ima_add_boot_aggregate(void)
 	struct integrity_iint_cache tmp_iint, *iint = &tmp_iint;
 	struct ima_event_data event_data = { .iint = iint,
 					     .filename = boot_aggregate_name };
+	struct ima_max_digest_data hash;
 	int result = -ENOMEM;
 	int violation = 0;
-	struct {
-		struct ima_digest_data hdr;
-		char digest[TPM_MAX_DIGEST_SIZE];
-	} hash;
 
 	memset(iint, 0, sizeof(*iint));
 	memset(&hash, 0, sizeof(hash));
-	iint->ima_hash = &hash.hdr;
+	iint->ima_hash = (struct ima_digest_data *)&hash;
 	iint->ima_hash->algo = ima_hash_algo;
 	iint->ima_hash->length = hash_digest_size[ima_hash_algo];
 
@@ -73,7 +70,8 @@ static int __init ima_add_boot_aggregate(void)
 	 * is not found.
 	 */
 	if (ima_tpm_chip) {
-		result = ima_calc_boot_aggregate(&hash.hdr);
+		result = ima_calc_boot_aggregate((struct ima_digest_data *)
+						  &hash);
 		if (result < 0) {
 			audit_cause = "hashing_error";
 			goto err_out;
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index d045dccd415a..ee2e6b7c7575 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -15,6 +15,7 @@
 #include <linux/types.h>
 #include <linux/integrity.h>
 #include <crypto/sha1.h>
+#include <crypto/hash.h>
 #include <linux/key.h>
 #include <linux/audit.h>
 
@@ -110,6 +111,29 @@ struct ima_digest_data {
 	u8 digest[];
 } __packed;
 
+/*
+ * Instead of dynamically allocating memory for the ima_digest_data struct
+ * with space for the specific hash algo or wrapping the ima_digest_data
+ * struct inside another local structure, define ima_max_digest_data struct
+ * with the maximum digest size.
+ */
+struct ima_max_digest_data {
+	u8 algo;
+	u8 length;
+	union {
+		struct {
+			u8 unused;
+			u8 type;
+		} sha1;
+		struct {
+			u8 type;
+			u8 algo;
+		} ng;
+		u8 data[2];
+	} xattr;
+	u8 digest[HASH_MAX_DIGESTSIZE];
+} __packed;
+
 /*
  * signature format v2 - for using with asymmetric keys
  */
-- 
2.27.0