cxgb4/ch_ktls: Fix undefined behavior bug in struct chcr_ktls_ofld_ctx_tx

struct tls_offload_context_tx is a flexible structure, which means that it contains a flexible-array member at the bottom. This could potentially lead to an overwrite of the objects following base in struct chcr_ktls_ofld_ctx_tx at run-time.

Notice that flexible-array member driver_state in struct tls_offload_context_tx can grow up to 16 bytes:

| include/net/tls.h-170:
| #define TLS_DRIVER_STATE_SIZE_TX 16

| include/net/tls.h-173:
| #define TLS_OFFLOAD_CONTEXT_SIZE_TX                                     \
|	(sizeof(struct tls_offload_context_tx) + TLS_DRIVER_STATE_SIZE_TX)

| net/tls/tls_device.c-1119:
| offload_ctx = kzalloc(TLS_OFFLOAD_CONTEXT_SIZE_TX, GFP_KERNEL);

Fix this by placing the declaration of object base at the end of struct chcr_ktls_ofld_ctx_tx.

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

---
Changes in v2:
- Update changelog text: mention -Wflex-array-member-not-at-end.

v1:
- Link: https://lore.kernel.org/linux-hardening/ZRvyysCUTqA7aXN4@work/

 drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 10572dc55365..35e34e3db663 100644
@@ -68,8 +68,8 @@ struct chcr_ktls_info {
 };
 
 struct chcr_ktls_ofld_ctx_tx {
-	struct tls_offload_context_tx base;
 	struct chcr_ktls_info *chcr_info;
+	struct tls_offload_context_tx base;
 };
 
 struct chcr_ktls_uld_ctx {

2.34.1

AFAIU, chcr_ktls_ofld_ctx_tx just misuses the extra space allocated by tls_set_device_offload. There's no bug, but the code is a bit confusing. I don't think this patch works, since chcr_ktls doesn't allocate its own memory for chcr_ktls_ofld_ctx_tx.

As part of a series of cleanups that I'll submit soon (hopefully this week), I updated chcr_ktls to use the driver_state part of tls_offload_context_tx (instead of the cast in chcr_get_ktls_tx_context), and then removed the flexarrays from tls_offload_context_tx and tls_offload_context_rx (since they're actually a fixed size).

Sabrina