From: Gustavo A. R. Silva <gustavo@embeddedor.com>
Date: Mon, 17 Feb 2020 19:59:41 +0000 (-0600)
Subject: NFC: digital: Replace zero-length array with flexible-array member
X-Git-Tag: Ubuntu-5.10.0-12.13~3211^2~403
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=9814428a44d63bf77831afdbb37b5f0aab7394c9;p=mirror_ubuntu-hirsute-kernel.git

NFC: digital: 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>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/nfc/digital_dep.c b/net/nfc/digital_dep.c
index 65aaa9d7c813..304b1a9bb18a 100644
--- a/net/nfc/digital_dep.c
+++ b/net/nfc/digital_dep.c
@@ -71,7 +71,7 @@ struct digital_atr_req {
 	u8 bs;
 	u8 br;
 	u8 pp;
-	u8 gb[0];
+	u8 gb[];
 } __packed;
 
 struct digital_atr_res {
@@ -83,7 +83,7 @@ struct digital_atr_res {
 	u8 br;
 	u8 to;
 	u8 pp;
-	u8 gb[0];
+	u8 gb[];
 } __packed;
 
 struct digital_psl_req {