[PATCH][next] crypto/nx: Avoid potential -Wflex-array-member-not-at-end warning

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

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

Use the `__struct_group()` helper to separate the flexible array
from the rest of the members in flexible `struct nx842_crypto_header`,
through tagged `struct nx842_crypto_header_hdr`, and avoid embedding
the flexible-array member in the middle of `struct nx842_crypto_ctx`.

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

This code was detected with the help of Coccinelle, and audited and
modified manually.

Link: https://github.com/KSPP/linux/issues/202
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/crypto/nx/nx-842.c |  6 ++++--
 drivers/crypto/nx/nx-842.h | 11 +++++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/crypto/nx/nx-842.c b/drivers/crypto/nx/nx-842.c
index 2ab90ec10e61..82214cde2bcd 100644
--- a/drivers/crypto/nx/nx-842.c
+++ b/drivers/crypto/nx/nx-842.c
@@ -251,7 +251,9 @@ int nx842_crypto_compress(struct crypto_tfm *tfm,
 			  u8 *dst, unsigned int *dlen)
 {
 	struct nx842_crypto_ctx *ctx = crypto_tfm_ctx(tfm);
-	struct nx842_crypto_header *hdr = &ctx->header;
+	struct nx842_crypto_header *hdr =
+				container_of(&ctx->header,
+					     struct nx842_crypto_header, hdr);
 	struct nx842_crypto_param p;
 	struct nx842_constraints c = *ctx->driver->constraints;
 	unsigned int groups, hdrsize, h;
@@ -490,7 +492,7 @@ int nx842_crypto_decompress(struct crypto_tfm *tfm,
 	}
 
 	memcpy(&ctx->header, src, hdr_len);
-	hdr = &ctx->header;
+	hdr = container_of(&ctx->header, struct nx842_crypto_header, hdr);
 
 	for (n = 0; n < hdr->groups; n++) {
 		/* ignore applies to last group */
diff --git a/drivers/crypto/nx/nx-842.h b/drivers/crypto/nx/nx-842.h
index 7590bfb24d79..1f42c83d2683 100644
--- a/drivers/crypto/nx/nx-842.h
+++ b/drivers/crypto/nx/nx-842.h
@@ -157,9 +157,12 @@ struct nx842_crypto_header_group {
 } __packed;
 
 struct nx842_crypto_header {
-	__be16 magic;		/* NX842_CRYPTO_MAGIC */
-	__be16 ignore;		/* decompressed end bytes to ignore */
-	u8 groups;		/* total groups in this header */
+	/* New members must be added within the __struct_group() macro below. */
+	__struct_group(nx842_crypto_header_hdr, hdr, __packed,
+		__be16 magic;		/* NX842_CRYPTO_MAGIC */
+		__be16 ignore;		/* decompressed end bytes to ignore */
+		u8 groups;		/* total groups in this header */
+	);
 	struct nx842_crypto_header_group group[];
 } __packed;
 
@@ -171,7 +174,7 @@ struct nx842_crypto_ctx {
 	u8 *wmem;
 	u8 *sbounce, *dbounce;
 
-	struct nx842_crypto_header header;
+	struct nx842_crypto_header_hdr header;
 	struct nx842_crypto_header_group group[NX842_CRYPTO_GROUP_MAX];
 
 	struct nx842_driver *driver;
-- 
2.34.1