On Thu, Apr 30, 2020 at 11:30:49PM +0200, Arnd Bergmann wrote:
> The current gcc-10 snapshot produces a false-positive warning:
>
> net/core/drop_monitor.c: In function 'trace_drop_common.constprop':
> cc1: error: writing 8 bytes into a region of size 0
> [-Werror=stringop-overflow=]
> In file included from net/core/drop_monitor.c:23:
> include/uapi/linux/net_dropmon.h:36:8: note: at offset 0 to object 'entries'
> with size 4 declared here
> 36 | __u32 entries;
> | ^~~~~~~
>
> I reported this in the gcc bugzilla, but in case it does not get
> fixed in the release, work around it by using a temporary variable.
>
> Fixes: 9a8afc8d3962 ("Network Drop Monitor: Adding drop monitor
> implementation & Netlink protocol")
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94881
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> ---
> net/core/drop_monitor.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
> index 8e33cec9fc4e..2ee7bc4c9e03 100644
> --- a/net/core/drop_monitor.c
> +++ b/net/core/drop_monitor.c
> @@ -213,6 +213,7 @@ static void sched_send_work(struct timer_list *t)
> static void trace_drop_common(struct sk_buff *skb, void *location)
> {
> struct net_dm_alert_msg *msg;
> + struct net_dm_drop_point *point;
> struct nlmsghdr *nlh;
> struct nlattr *nla;
> int i;
> @@ -231,11 +232,13 @@ static void trace_drop_common(struct sk_buff *skb, void
> *location)
> nlh = (struct nlmsghdr *)dskb->data;
> nla = genlmsg_data(nlmsg_data(nlh));
> msg = nla_data(nla);
> + point = msg->points;
> for (i = 0; i < msg->entries; i++) {
> - if (!memcmp(&location, msg->points[i].pc, sizeof(void *))) {
> - msg->points[i].count++;
> + if (!memcmp(&location, &point->pc, sizeof(void *))) {
> + point->count++;
> goto out;
> }
> + point++;
> }
> if (msg->entries == dm_hit_limit)
> goto out;
> @@ -244,8 +247,8 @@ static void trace_drop_common(struct sk_buff *skb, void
> *location)
> */
> __nla_reserve_nohdr(dskb, sizeof(struct net_dm_drop_point));
> nla->nla_len += NLA_ALIGN(sizeof(struct net_dm_drop_point));
> - memcpy(msg->points[msg->entries].pc, &location, sizeof(void *));
> - msg->points[msg->entries].count = 1;
> + memcpy(point->pc, &location, sizeof(void *));
> + point->count = 1;
> msg->entries++;
>
> if (!timer_pending(&data->send_timer)) {
Acked-by: Neil Horman <nhor...@tuxdriver.com>
