drop_monitor: work around gcc-10 stringop-overflow warning

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 <arnd@arndb.de>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 8e33cec..2ee7bc4 100644 (file)
--- 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)) {