From 5c91aa1df00ec4fa283c35e92736392df3137d81 Mon Sep 17 00:00:00 2001
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 23 Mar 2020 19:22:24 -0500
Subject: [PATCH] skbuff.h: Replace zero-length array with flexible-array
member
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>
---
include/linux/skbuff.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3a2ac7072dbba1..3000c526f5526c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4162,7 +4162,7 @@ struct skb_ext {
refcount_t refcnt;
u8 offset[SKB_EXT_NUM]; /* in chunks of 8 bytes */
u8 chunks; /* same */
- char data[0] __aligned(8);
+ char data[] __aligned(8);
};
struct skb_ext *__skb_ext_alloc(void);
--
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