integrity: Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
ready to enable it globally.

There is currently an object (`hdr)` in `struct ima_max_digest_data`
that contains a flexible structure (`struct ima_digest_data`):

 struct ima_max_digest_data {
        struct ima_digest_data hdr;
        u8 digest[HASH_MAX_DIGESTSIZE];
 } __packed;

So, in order to avoid ending up with a flexible-array member in the
middle of a struct, we use the `__struct_group()` helper to separate
the flexible array from the rest of the members in the flexible
structure:

struct ima_digest_data {
        __struct_group(ima_digest_data_hdr, hdr, __packed,

        ... the rest of the members

        );
        u8 digest[];
} __packed;

And similarly for `struct evm_ima_xattr_data`.

With the change described above, we can now declare an object of the
type of the tagged `struct ima_digest_data_hdr`, without embedding the
flexible array in the middle of another struct:

 struct ima_max_digest_data {
        struct ima_digest_data_hdr hdr;
        u8 digest[HASH_MAX_DIGESTSIZE];
 } __packed;

And similarly for `struct evm_digest` and `struct evm_xattr`.

We also use `container_of()` whenever we need to retrieve a pointer to
the flexible structure.

So, with these changes, fix the following warnings:

security/integrity/evm/evm.h:64:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/evm/../integrity.h:40:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/evm/../integrity.h:68:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/ima/../integrity.h:40:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/ima/../integrity.h:68:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/integrity.h:40:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/integrity.h:68:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/platform_certs/../integrity.h:40:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
security/integrity/platform_certs/../integrity.h:68:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: https://github.com/KSPP/linux/issues/202
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/evm/evm.h

@@ -61,7 +61,7 @@ extern int evm_hmac_attrs;
 extern struct list_head evm_config_xattrnames;
 
 struct evm_digest {
-	struct ima_digest_data hdr;
+	struct ima_digest_data_hdr hdr;
 	char digest[IMA_MAX_DIGEST_SIZE];
 } __packed;
 

security/integrity/ima/ima_api.c

@@ -246,6 +246,8 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
 	struct inode *inode = file_inode(file);
 	struct inode *real_inode = d_real_inode(file_dentry(file));
 	struct ima_max_digest_data hash;
+	struct ima_digest_data *hash_hdr = container_of(&hash.hdr,
+						struct ima_digest_data, hdr);
 	struct name_snapshot filename;
 	struct kstat stat;
 	int result = 0;
@@ -286,9 +288,9 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
 			result = -ENODATA;
 		}
 	} else if (buf) {
-		result = ima_calc_buffer_hash(buf, size, &hash.hdr);
+		result = ima_calc_buffer_hash(buf, size, hash_hdr);
 	} else {
-		result = ima_calc_file_hash(file, &hash.hdr);
+		result = ima_calc_file_hash(file, hash_hdr);
 	}
 
 	if (result && result != -EBADF && result != -EINVAL)

security/integrity/ima/ima_appraise.c

@@ -378,7 +378,9 @@ static int xattr_verify(enum ima_hooks func, struct ima_iint_cache *iint,
 		}
 
 		rc = calc_file_id_hash(IMA_VERITY_DIGSIG, iint->ima_hash->algo,
-				       iint->ima_hash->digest, &hash.hdr);
+				       iint->ima_hash->digest,
+				       container_of(&hash.hdr,
+					       struct ima_digest_data, hdr));
 		if (rc) {
 			*cause = "sigv3-hashing-error";
 			*status = INTEGRITY_FAIL;

security/integrity/ima/ima_init.c

@@ -48,12 +48,14 @@ static int __init ima_add_boot_aggregate(void)
 	struct ima_event_data event_data = { .iint = iint,
 					     .filename = boot_aggregate_name };
 	struct ima_max_digest_data hash;
+	struct ima_digest_data *hash_hdr = container_of(&hash.hdr,
+						struct ima_digest_data, hdr);
 	int result = -ENOMEM;
 	int violation = 0;
 
 	memset(iint, 0, sizeof(*iint));
 	memset(&hash, 0, sizeof(hash));
-	iint->ima_hash = &hash.hdr;
+	iint->ima_hash = hash_hdr;
 	iint->ima_hash->algo = ima_hash_algo;
 	iint->ima_hash->length = hash_digest_size[ima_hash_algo];
 
@@ -70,7 +72,7 @@ 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(hash_hdr);
 		if (result < 0) {
 			audit_cause = "hashing_error";
 			goto err_out;

security/integrity/ima/ima_main.c

@@ -948,6 +948,8 @@ int process_buffer_measurement(struct mnt_idmap *idmap,
 					    .buf_len = size};
 	struct ima_template_desc *template;
 	struct ima_max_digest_data hash;
+	struct ima_digest_data *hash_hdr = container_of(&hash.hdr,
+						struct ima_digest_data, hdr);
 	char digest_hash[IMA_MAX_DIGEST_SIZE];
 	int digest_hash_len = hash_digest_size[ima_hash_algo];
 	int violation = 0;
@@ -986,7 +988,7 @@ int process_buffer_measurement(struct mnt_idmap *idmap,
 	if (!pcr)
 		pcr = CONFIG_IMA_MEASURE_PCR_IDX;
 
-	iint.ima_hash = &hash.hdr;
+	iint.ima_hash = hash_hdr;
 	iint.ima_hash->algo = ima_hash_algo;
 	iint.ima_hash->length = hash_digest_size[ima_hash_algo];
 
@@ -997,7 +999,7 @@ int process_buffer_measurement(struct mnt_idmap *idmap,
 	}
 
 	if (buf_hash) {
-		memcpy(digest_hash, hash.hdr.digest, digest_hash_len);
+		memcpy(digest_hash, hash_hdr->digest, digest_hash_len);
 
 		ret = ima_calc_buffer_hash(digest_hash, digest_hash_len,
 					   iint.ima_hash);

security/integrity/ima/ima_template_lib.c

@@ -339,6 +339,8 @@ int ima_eventdigest_init(struct ima_event_data *event_data,
 			 struct ima_field_data *field_data)
 {
 	struct ima_max_digest_data hash;
+	struct ima_digest_data *hash_hdr = container_of(&hash.hdr,
+						struct ima_digest_data, hdr);
 	u8 *cur_digest = NULL;
 	u32 cur_digestsize = 0;
 	struct inode *inode;
@@ -358,7 +360,7 @@ int ima_eventdigest_init(struct ima_event_data *event_data,
 	if ((const char *)event_data->filename == boot_aggregate_name) {
 		if (ima_tpm_chip) {
 			hash.hdr.algo = HASH_ALGO_SHA1;
-			result = ima_calc_boot_aggregate(&hash.hdr);
+			result = ima_calc_boot_aggregate(hash_hdr);
 
 			/* algo can change depending on available PCR banks */
 			if (!result && hash.hdr.algo != HASH_ALGO_SHA1)
@@ -368,7 +370,7 @@ int ima_eventdigest_init(struct ima_event_data *event_data,
 				memset(&hash, 0, sizeof(hash));
 		}
 
-		cur_digest = hash.hdr.digest;
+		cur_digest = hash_hdr->digest;
 		cur_digestsize = hash_digest_size[HASH_ALGO_SHA1];
 		goto out;
 	}
@@ -379,14 +381,14 @@ int ima_eventdigest_init(struct ima_event_data *event_data,
 	inode = file_inode(event_data->file);
 	hash.hdr.algo = ima_template_hash_algo_allowed(ima_hash_algo) ?
 	    ima_hash_algo : HASH_ALGO_SHA1;
-	result = ima_calc_file_hash(event_data->file, &hash.hdr);
+	result = ima_calc_file_hash(event_data->file, hash_hdr);
 	if (result) {
 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
 				    event_data->filename, "collect_data",
 				    "failed", result, 0);
 		return result;
 	}
-	cur_digest = hash.hdr.digest;
+	cur_digest = hash_hdr->digest;
 	cur_digestsize = hash.hdr.length;
 out:
 	return ima_eventdigest_init_common(cur_digest, cur_digestsize,

security/integrity/integrity.h

@@ -31,19 +31,24 @@ enum evm_ima_xattr_type {
 };
 
 struct evm_ima_xattr_data {
-	u8 type;
+	/* New members must be added within the __struct_group() macro below. */
+	__struct_group(evm_ima_xattr_data_hdr, hdr, __packed,
+		u8 type;
+	);
 	u8 data[];
 } __packed;
 
 /* Only used in the EVM HMAC code. */
 struct evm_xattr {
-	struct evm_ima_xattr_data data;
+	struct evm_ima_xattr_data_hdr data;
 	u8 digest[SHA1_DIGEST_SIZE];
 } __packed;
 
 #define IMA_MAX_DIGEST_SIZE	HASH_MAX_DIGESTSIZE
 
 struct ima_digest_data {
+	/* New members must be added within the __struct_group() macro below. */
+	__struct_group(ima_digest_data_hdr, hdr, __packed,
 	u8 algo;
 	u8 length;
 	union {
@@ -57,6 +62,7 @@ struct ima_digest_data {
 		} ng;
 		u8 data[2];
 	} xattr;
+	);
 	u8 digest[];
 } __packed;
 
@@ -65,7 +71,7 @@ struct ima_digest_data {
  * with the maximum hash size, define ima_max_digest_data struct.
  */
 struct ima_max_digest_data {
-	struct ima_digest_data hdr;
+	struct ima_digest_data_hdr hdr;
 	u8 digest[HASH_MAX_DIGESTSIZE];
 } __packed;