linux-kernel - [PATCH v2] Fix initializing a static union variable

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Date: Fri, 21 Jun 2024 14:18:19 -0700
From: Yabin Cui <yabinc@...gle.com>
To: Steffen Klassert <steffen.klassert@...unet.com>, Herbert Xu <herbert@...dor.apana.org.au>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	Yabin Cui <yabinc@...gle.com>
Subject: [PATCH v2] Fix initializing a static union variable

saddr_wildcard is a static union variable initialized with {}.

Empty brace initialization of union types is unspecified prior to C23,
and even in C23, it doesn't guarantee zero initialization of all fields
(see sections 4.5 and 6.2 in
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2900.htm).

Clang currently only initializes the first field to zero, leaving other
fields undefined. This can lead to unexpected behavior and optimizations
that produce random values (with some optimization flags).
See https://godbolt.org/z/hxnT1PTWo.

The issue has been reported to Clang upstream (
https://github.com/llvm/llvm-project/issues/78034#issuecomment-2183233517).
This commit mitigates the problem by avoiding empty brace initialization
in saddr_wildcard.

Fixes: 08ec9af1c062 ("xfrm: Fix xfrm_state_find() wrt. wildcard source address.")
Signed-off-by: Yabin Cui <yabinc@...gle.com>

---

Changes in v2:
- Update commit message to add/update links.

---
 net/xfrm/xfrm_state.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 649bb739df0d..9bc69d703e5c 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1139,7 +1139,7 @@ xfrm_state_find(const xfrm_address_t *daddr, const xfrm_address_t *saddr,
 		struct xfrm_policy *pol, int *err,
 		unsigned short family, u32 if_id)
 {
-	static xfrm_address_t saddr_wildcard = { };
+	static const xfrm_address_t saddr_wildcard;
 	struct net *net = xp_net(pol);
 	unsigned int h, h_wildcard;
 	struct xfrm_state *x, *x0, *to_put;
-- 
2.45.2.741.gdbec12cfda-goog