linux-kernel - [PATCH 07/15] drop_monitor: work around gcc-10 stringop-overflow warning

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Message-Id: <20200430213101.135134-8-arnd@arndb.de>
Date:   Thu, 30 Apr 2020 23:30:49 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-kernel@...r.kernel.org, Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Ido Schimmel <idosch@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, Joe Perches <joe@...ches.com>,
        netdev@...r.kernel.org
Subject: [PATCH 07/15] 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@...db.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)) {
-- 
2.26.0