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@secunet.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index 23543c33fee823064d59b5fb958be11bcfed8f77..6a77328be114525b5eabd8138c25fc1b99d517b0 100644 (file)
--- 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 */