[PATCH 5.6 020/194] drop_monitor: work around gcc-10 stringop-overflow warning

Greg Kroah-Hartman
2020-05-18T18:00:33Z

From: Arnd Bergmann <arnd@arndb.de>

[ Upstream commit dc30b4059f6e2abf3712ab537c8718562b21c45d ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 31700e0c39283..04d8e8779384d 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -212,6 +212,7 @@ 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;
@@ -230,11 +231,13 @@ 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;
@@ -243,8 +246,8 @@ 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)) {
--
2.20.1