linux-hardening - [PATCH] enic: Avoid false positive under FORTIFY

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Date: Fri, 16 Feb 2024 15:30:05 -0800
From: Kees Cook <keescook@...omium.org>
To: Christian Benvenuti <benve@...co.com>
Cc: Kees Cook <keescook@...omium.org>,
	Satish Kharat <satishkh@...co.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A . R . Silva" <gustavo@...eddedor.com>,
	netdev@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] enic: Avoid false positive under FORTIFY_SOURCE

FORTIFY_SOURCE has been ignoring 0-sized destinations while the kernel
code base has been converted to flexible arrays. In order to enforce
the 0-sized destinations (e.g. with __counted_by), the remaining 0-sized
destinations need to be handled. Unfortunately, struct vic_provinfo
resists full conversion, as it contains a flexible array of flexible
arrays, which is only possible with the 0-sized fake flexible array.

Use unsafe_memcpy() to avoid future false positives under
CONFIG_FORTIFY_SOURCE.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: Christian Benvenuti <benve@...co.com>
Cc: Satish Kharat <satishkh@...co.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: Gustavo A. R. Silva <gustavo@...eddedor.com>
Cc: netdev@...r.kernel.org
---
 drivers/net/ethernet/cisco/enic/vnic_vic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cisco/enic/vnic_vic.c b/drivers/net/ethernet/cisco/enic/vnic_vic.c
index 20fcb20b42ed..66b577835338 100644
--- a/drivers/net/ethernet/cisco/enic/vnic_vic.c
+++ b/drivers/net/ethernet/cisco/enic/vnic_vic.c
@@ -49,7 +49,8 @@ int vic_provinfo_add_tlv(struct vic_provinfo *vp, u16 type, u16 length,
 
 	tlv->type = htons(type);
 	tlv->length = htons(length);
-	memcpy(tlv->value, value, length);
+	unsafe_memcpy(tlv->value, value, length,
+		      /* Flexible array of flexible arrays */);
 
 	vp->num_tlvs = htonl(ntohl(vp->num_tlvs) + 1);
 	vp->length = htonl(ntohl(vp->length) +
-- 
2.34.1