Bluetooth: 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: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/net/bluetooth/a2mp.h b/net/bluetooth/a2mp.h
index 0029d5119be6..2fd253a61a2a 100644
--- a/net/bluetooth/a2mp.h
+++ b/net/bluetooth/a2mp.h
@@ -36,14 +36,14 @@ struct a2mp_cmd {
 	__u8	code;
 	__u8	ident;
 	__le16	len;
-	__u8	data[0];
+	__u8	data[];
 } __packed;
 
 /* A2MP command codes */
 #define A2MP_COMMAND_REJ         0x01
 struct a2mp_cmd_rej {
 	__le16	reason;
-	__u8	data[0];
+	__u8	data[];
 } __packed;
 
 #define A2MP_DISCOVER_REQ        0x02
@@ -62,7 +62,7 @@ struct a2mp_cl {
 struct a2mp_discov_rsp {
 	__le16     mtu;
 	__le16     ext_feat;
-	struct a2mp_cl cl[0];
+	struct a2mp_cl cl[];
 } __packed;
 
 #define A2MP_CHANGE_NOTIFY       0x04
@@ -93,7 +93,7 @@ struct a2mp_amp_assoc_req {
 struct a2mp_amp_assoc_rsp {
 	__u8	id;
 	__u8	status;
-	__u8	amp_assoc[0];
+	__u8	amp_assoc[];
 } __packed;
 
 #define A2MP_CREATEPHYSLINK_REQ  0x0A
@@ -101,7 +101,7 @@ struct a2mp_amp_assoc_rsp {
 struct a2mp_physlink_req {
 	__u8	local_id;
 	__u8	remote_id;
-	__u8	amp_assoc[0];
+	__u8	amp_assoc[];
 } __packed;
 
 #define A2MP_CREATEPHYSLINK_RSP  0x0B