linux-stable/include/net/mpls_iptunnel.h
Gustavo A. R. Silva 680a93166e net: mpls: 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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-02-28 12:08:37 -08:00

22 lines
429 B
C

/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (c) 2015 Cumulus Networks, Inc.
*/
#ifndef _NET_MPLS_IPTUNNEL_H
#define _NET_MPLS_IPTUNNEL_H 1
struct mpls_iptunnel_encap {
u8 labels;
u8 ttl_propagate;
u8 default_ttl;
u8 reserved1;
u32 label[];
};
static inline struct mpls_iptunnel_encap *mpls_lwtunnel_encap(struct lwtunnel_state *lwtstate)
{
return (struct mpls_iptunnel_encap *)lwtstate->data;
}
#endif