netdev - [PATCH] xfrm: Annotate struct xfrm_sec_ctx with __counted

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Date: Tue,  3 Oct 2023 16:18:28 -0700
From: Kees Cook <keescook@...omium.org>
To: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Kees Cook <keescook@...omium.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	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] xfrm: Annotate struct xfrm_sec_ctx 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 xfrm_sec_ctx.

Cc: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: "David S. Miller" <davem@...emloft.net>
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/uapi/linux/xfrm.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index 23543c33fee8..6a77328be114 100644
--- a/include/uapi/linux/xfrm.h
+++ b/include/uapi/linux/xfrm.h
@@ -4,6 +4,7 @@
 
 #include <linux/in6.h>
 #include <linux/types.h>
+#include <linux/stddef.h>
 
 /* All of the structures in this file may not change size as they are
  * passed into the kernel from userspace via netlink sockets.
@@ -33,7 +34,7 @@ struct xfrm_sec_ctx {
 	__u8	ctx_alg;
 	__u16	ctx_len;
 	__u32	ctx_sid;
-	char	ctx_str[];
+	char	ctx_str[] __counted_by(ctx_len);
 };
 
 /* Security Context Domains of Interpretation */
-- 
2.34.1