linux-kernel - [PATCH] nexthop: Annotate struct nh_group with __counted

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Date:   Tue,  3 Oct 2023 18:44:49 -0700
From:   Kees Cook <keescook@...omium.org>
To:     David Ahern <dsahern@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        "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,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH] nexthop: Annotate struct nh_group with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct nh_group.

Cc: David Ahern <dsahern@...nel.org>
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
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/net/nexthop.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/nexthop.h b/include/net/nexthop.h
index 8f5a2ab45920..d92046a4a078 100644
--- a/include/net/nexthop.h
+++ b/include/net/nexthop.h
@@ -126,7 +126,7 @@ struct nh_group {
 	bool			has_v4;
 
 	struct nh_res_table __rcu *res_table;
-	struct nh_grp_entry	nh_entries[];
+	struct nh_grp_entry	nh_entries[] __counted_by(num_nh);
 };
 
 struct nexthop {
-- 
2.34.1