flow_dissector: Fix out-of-bounds warnings

Fix the following out-of-bounds warnings:

net/core/flow_dissector.c: In function '__skb_flow_dissect':

     1104 |    memcpy(&key_addrs->v6addrs, &iph->saddr,
          |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     1105 |           sizeof(key_addrs->v6addrs));
          |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~

In file included from include/linux/ipv6.h:5,
from net/core/flow_dissector.c:6:
include/uapi/linux/ipv6.h:133:18: note: subobject 'saddr' declared here
133 | struct in6_addr saddr;
| ^~~~~

     1059 |    memcpy(&key_addrs->v4addrs, &iph->saddr,
          |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     1060 |           sizeof(key_addrs->v4addrs));
          |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~

In file included from include/linux/ip.h:17,
from net/core/flow_dissector.c:5:
include/uapi/linux/ip.h:103:9: note: subobject 'saddr' declared here
103 | __be32 saddr;
| ^~~~~

The problem is that the original code is trying to copy data into a couple of struct members adjacent to each other in a single call to memcpy(). So, the compiler legitimately complains about it. As these are just a couple of members, fix this by copying each one of them in separate calls to memcpy().

This helps with the ongoing efforts to globally enable -Warray-bounds and get us closer to being able to tighten the FORTIFY_SOURCE routines on memcpy().

---
 net/core/flow_dissector.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

index 2aadbfc5193b..39d7be03e568 100644
@@ -1056,8 +1056,10 @@ bool __skb_flow_dissect(const struct net *net,
 							      FLOW_DISSECTOR_KEY_IPV4_ADDRS,
 							      target_container);
 
-			memcpy(&key_addrs->v4addrs, &iph->saddr,
-			       sizeof(key_addrs->v4addrs));
+			memcpy(&key_addrs->v4addrs.src, &iph->saddr,
+			       sizeof(key_addrs->v4addrs.src));
+			memcpy(&key_addrs->v4addrs.dst, &iph->daddr,
+			       sizeof(key_addrs->v4addrs.dst));
 			key_control->addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
 		}
 

@@ -1101,8 +1103,10 @@ bool __skb_flow_dissect(const struct net *net,
 							      FLOW_DISSECTOR_KEY_IPV6_ADDRS,
 							      target_container);
 
-			memcpy(&key_addrs->v6addrs, &iph->saddr,
-			       sizeof(key_addrs->v6addrs));
+			memcpy(&key_addrs->v6addrs.src, &iph->saddr,
+			       sizeof(key_addrs->v6addrs.src));
+			memcpy(&key_addrs->v6addrs.dst, &iph->daddr,
+			       sizeof(key_addrs->v6addrs.dst));
 			key_control->addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
 		}
 

2.27.0