linux-kernel - [PATCH net-next 2/2] net: openvswitch: Annotate struct mask_array with __counted_byUse struct

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Message-Id: <f66ddcf1ef9328f10292ea75a17b584359b6cde3.1696156198.git.christophe.jaillet@wanadoo.fr>
Date:   Sun,  1 Oct 2023 13:07:23 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     keescook@...omium.org, Pravin B Shelar <pshelar@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>
Cc:     linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        netdev@...r.kernel.org, dev@...nvswitch.org, llvm@...ts.linux.dev
Subject: [PATCH net-next 2/2] net: openvswitch: Annotate struct mask_array with __counted_byUse struct_size()

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 checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
This patch is part of a work done in parallel of what is currently worked
on by Kees Cook.

My patches are only related to corner cases that do NOT match the
semantic of his Coccinelle script[1].

In this case, in tbl_mask_array_alloc(), several things are allocated with
a single allocation. Then, some pointer arithmetic computes the address of
the memory after the flex-array.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
---
 net/openvswitch/flow_table.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
index 9e659db78c05..8d9e83b4d62c 100644
--- a/net/openvswitch/flow_table.h
+++ b/net/openvswitch/flow_table.h
@@ -48,7 +48,7 @@ struct mask_array {
 	int count, max;
 	struct mask_array_stats __percpu *masks_usage_stats;
 	u64 *masks_usage_zero_cntr;
-	struct sw_flow_mask __rcu *masks[];
+	struct sw_flow_mask __rcu *masks[] __counted_by(size);
 };
 
 struct table_instance {
-- 
2.34.1