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net: sched: 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 2020-02-27 14:58:44 -06:00 committed by David S. Miller
parent 9f0ca0c1a5
commit b90feaff2a
5 changed files with 5 additions and 5 deletions
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2
include/net/pkt_sched.h
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@ -181,7 +181,7 @@ struct tc_taprio_qopt_offload {
u64 cycle_time_extension;
size_t num_entries;
struct tc_taprio_sched_entry entries[0];
struct tc_taprio_sched_entry entries[];
};
/* Reference counting */

2
net/sched/em_ipt.c
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@ -22,7 +22,7 @@ struct em_ipt_match {
const struct xt_match *match;
u32 hook;
u8 nfproto;
u8 match_data[0] __aligned(8);
u8 match_data[] __aligned(8);
};
struct em_ipt_xt_match {

2
net/sched/em_nbyte.c
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@ -16,7 +16,7 @@
struct nbyte_data {
struct tcf_em_nbyte hdr;
char pattern[0];
char pattern[];
};
static int em_nbyte_change(struct net *net, void *data, int data_len,

2
net/sched/sch_atm.c
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@ -58,7 +58,7 @@ struct atm_flow_data {
struct atm_flow_data *excess; /* flow for excess traffic;
NULL to set CLP instead */
int hdr_len;
unsigned char hdr[0]; /* header data; MUST BE LAST */
unsigned char hdr[]; /* header data; MUST BE LAST */
};
struct atm_qdisc_data {

2
net/sched/sch_netem.c
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@ -66,7 +66,7 @@
struct disttable {
u32 size;
s16 table[0];
s16 table[];
};
struct netem_sched_data {