linux-kernel - [PATCH][next] flow_dissector: Fix out-of-bounds warning in __skb_flow_bpf_to

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Message-ID: <20210416193151.GA591935@embeddedor>
Date:   Fri, 16 Apr 2021 14:31:51 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] flow_dissector: Fix out-of-bounds warning in
 __skb_flow_bpf_to_target()

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@...el.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 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 5985029e43d4..3ed7c98a98e1 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -832,8 +832,10 @@ static void __skb_flow_bpf_to_target(const struct bpf_flow_keys *flow_keys,
 		key_addrs = skb_flow_dissector_target(flow_dissector,
 						      FLOW_DISSECTOR_KEY_IPV6_ADDRS,
 						      target_container);
-		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;
 	}
 
-- 
2.27.0