linux-kernel - [PATCH v2][next] cxgb4/ch_ktls: Fix undefined behavior bug in struct chcr_ktls_ofld_ctx

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Message-ID: <ZRvzdlvlbX4+eIln@work>
Date:   Tue, 3 Oct 2023 12:56:54 +0200
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Ayush Sawal <ayush.sawal@...lsio.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rohit Maheshwari <rohitm@...lsio.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH v2][next] 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.

Fixes: 34aba2c45024 ("cxgb4/chcr : Register to tls add and del callback")
Cc: stable@...r.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
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(-)

diff --git a/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.h b/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.h
index 10572dc55365..35e34e3db663 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.h
+++ b/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.h
@@ -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