net: sched: 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/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 6a70845..20d2c64 100644 (file)
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -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 */

diff --git a/net/sched/em_ipt.c b/net/sched/em_ipt.c
index 9fff648..eecfe07 100644 (file)
--- a/net/sched/em_ipt.c
+++ b/net/sched/em_ipt.c
@@ -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 {

diff --git a/net/sched/em_nbyte.c b/net/sched/em_nbyte.c
index 88c7ce4..2c1192a 100644 (file)
--- a/net/sched/em_nbyte.c
+++ b/net/sched/em_nbyte.c
@@ -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,

diff --git a/net/sched/sch_atm.c b/net/sched/sch_atm.c
index f4f9b8c..ee12ca9 100644 (file)
--- a/net/sched/sch_atm.c
+++ b/net/sched/sch_atm.c
@@ -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 {

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 42e557d..84f8277 100644 (file)
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -66,7 +66,7 @@
 
 struct disttable {
        u32  size;
-       s16 table[0];
+       s16 table[];
 };
 
 struct netem_sched_data {