[PATCH AUTOSEL 5.12 085/116] flow_dissector: Fix out-of-bounds warning in __skb_flow_bpf_to_target()

From: Sasha Levin
Date: Wed May 05 2021 - 12:39:51 EST

From: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>

[ Upstream commit 1e3d976dbb23b3fce544752b434bdc32ce64aabc ]

Fix the following out-of-bounds warning:

net/core/flow_dissector.c:835:3: warning: 'memcpy' offset [33, 48] from the object at 'flow_keys' is out of the bounds of referenced subobject 'ipv6_src' with type '__u32[4]' {aka 'unsigned int[4]'} at offset 16 [-Warray-bounds]

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().

Link: https://github.com/KSPP/linux/issues/109
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
net/core/flow_dissector.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index a96a4f5de0ce..3f36b04d86a0 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -828,8 +828,10 @@ static void __skb_flow_bpf_to_target(const struct bpf_flow_keys *flow_keys,
key_addrs = skb_flow_dissector_target(flow_dissector,
- memcpy(&key_addrs->v6addrs, &flow_keys->ipv6_src,
- sizeof(key_addrs->v6addrs));
+ memcpy(&key_addrs->v6addrs.src, &flow_keys->ipv6_src,
+ sizeof(key_addrs->v6addrs.src));
+ memcpy(&key_addrs->v6addrs.dst, &flow_keys->ipv6_dst,
+ sizeof(key_addrs->v6addrs.dst));
key_control->addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;