linux-kernel - [PATCH 5.4 101/260] ipv4: ip_output.c: Fix out-of-bounds warning in ip_copy

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Message-Id: <20210920163934.564505447@linuxfoundation.org>
Date:   Mon, 20 Sep 2021 18:41:59 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, kernel test robot <lkp@...el.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 101/260] ipv4: ip_output.c: Fix out-of-bounds warning in ip_copy_addrs()

From: Gustavo A. R. Silva <gustavoars@...nel.org>

[ Upstream commit 6321c7acb82872ef6576c520b0e178eaad3a25c0 ]

Fix the following out-of-bounds warning:

    In function 'ip_copy_addrs',
        inlined from '__ip_queue_xmit' at net/ipv4/ip_output.c:517:2:
net/ipv4/ip_output.c:449:2: warning: 'memcpy' offset [40, 43] from the object at 'fl' is out of the bounds of referenced subobject 'saddr' with type 'unsigned int' at offset 36 [-Warray-bounds]
      449 |  memcpy(&iph->saddr, &fl4->saddr,
          |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      450 |         sizeof(fl4->saddr) + sizeof(fl4->daddr));
          |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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(). This causes a legitimate compiler warning because memcpy()
overruns the length of &iph->saddr and &fl4->saddr. As these are just
a couple of struct members, fix this by using direct assignments,
instead of 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>
Link: https://lore.kernel.org/lkml/d5ae2e65-1f18-2577-246f-bada7eee6ccd@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/ipv4/ip_output.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index f52bc9c22e5b..0ec529d77a56 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -446,8 +446,9 @@ static void ip_copy_addrs(struct iphdr *iph, const struct flowi4 *fl4)
 {
 	BUILD_BUG_ON(offsetof(typeof(*fl4), daddr) !=
 		     offsetof(typeof(*fl4), saddr) + sizeof(fl4->saddr));
-	memcpy(&iph->saddr, &fl4->saddr,
-	       sizeof(fl4->saddr) + sizeof(fl4->daddr));
+
+	iph->saddr = fl4->saddr;
+	iph->daddr = fl4->daddr;
 }
 
 /* Note: skb->sk can be different from sk, in case of tunnels */
-- 
2.30.2