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>

1 files changed, 9 insertions, 3 deletions

diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 50d6f798e613..660f76cb69d3 100644
--- a/security/integrity/integrity.h
+++ b/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;