From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 17 Feb 2020 14:01:11 -0600
Subject: bpf, sockmap: Replace zero-length array with flexible-array member
Patch-mainline: v5.7-rc1
Git-commit: 45a4296b6e55ef2fbbe5946582822daf8f0f2e71
References: bsc#1177028

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Gary Lin <glin@suse.com>
---
 net/core/sock_map.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -520,7 +520,7 @@ struct bpf_htab_elem {
 	u32 hash;
 	struct sock *sk;
 	struct hlist_node node;
-	u8 key[0];
+	u8 key[];
 };
 
 struct bpf_htab_bucket {