linux-hardening - [PATCH] mlxsw: core_acl_flex_actions: Split memcpy() of struct flow_action

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Message-Id: <20220927004033.1942992-1-keescook@chromium.org>
Date:   Mon, 26 Sep 2022 17:40:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ido Schimmel <idosch@...dia.com>
Cc:     Kees Cook <keescook@...omium.org>, Petr Machata <petrm@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] mlxsw: core_acl_flex_actions: Split memcpy() of struct flow_action_cookie flexible array

To work around a misbehavior of the compiler's ability to see into
composite flexible array structs (as detailed in the coming memcpy()
hardening series[1]), split the memcpy() of the header and the payload
so no false positive run-time overflow warning will be generated.

[1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org

Cc: Ido Schimmel <idosch@...dia.com>
Cc: Petr Machata <petrm@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c b/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c
index 636db9a87457..9dfe7148199f 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_actions.c
@@ -737,8 +737,9 @@ mlxsw_afa_cookie_create(struct mlxsw_afa *mlxsw_afa,
 	if (!cookie)
 		return ERR_PTR(-ENOMEM);
 	refcount_set(&cookie->ref_count, 1);
-	memcpy(&cookie->fa_cookie, fa_cookie,
-	       sizeof(*fa_cookie) + fa_cookie->cookie_len);
+	cookie->fa_cookie = *fa_cookie;
+	memcpy(cookie->fa_cookie.cookie, fa_cookie->cookie,
+	       fa_cookie->cookie_len);
 
 	err = rhashtable_insert_fast(&mlxsw_afa->cookie_ht, &cookie->ht_node,
 				     mlxsw_afa_cookie_ht_params);
-- 
2.34.1