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ndisc: Replace zero-length array with flexible-array member

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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>
This commit is contained in:
Gustavo A. R. Silva 2020-02-28 18:53:11 -06:00 committed by David S. Miller
parent c61a2a76e5
commit 53e76f4824
1 changed files with 3 additions and 3 deletions
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6
include/net/ndisc.h
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@ -80,12 +80,12 @@ extern struct neigh_table nd_tbl;
struct nd_msg {
struct icmp6hdr icmph;
struct in6_addr target;
__u8 opt[0];
__u8 opt[];
};
struct rs_msg {
struct icmp6hdr icmph;
__u8 opt[0];
__u8 opt[];
};
struct ra_msg {
@ -98,7 +98,7 @@ struct rd_msg {
struct icmp6hdr icmph;
struct in6_addr target;
struct in6_addr dest;
__u8 opt[0];
__u8 opt[];
};
struct nd_opt_hdr {