| Message ID | 20200227205844.GA18578@embeddedor |
|---|---|
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
| Series | [next] net: sched: Replace zero-length array with flexible-array member | expand |
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com> Date: Thu, 27 Feb 2020 14:58:44 -0600 > 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> Applied, thank you.
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h index 6a70845bd9ab..20d2c6419612 100644 --- 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 9fff6480acc6..eecfe072c508 100644 --- 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 88c7ce42df7e..2c1192a2ee5e 100644 --- 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 f4f9b8cdbffb..ee12ca9f55b4 100644 --- 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 42e557d48e4e..84f82771cdf5 100644 --- 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 {
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> --- include/net/pkt_sched.h | 2 +- net/sched/em_ipt.c | 2 +- net/sched/em_nbyte.c | 2 +- net/sched/sch_atm.c | 2 +- net/sched/sch_netem.c | 2 +- 5 files changed, 5 insertions(+), 5 deletions(-)