linux-hardening - [PATCH] hv_netvsc: Avoid field-overflowing memcpy()

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Date:   Mon, 21 Jun 2021 15:21:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "K. Y. Srinivasan" <kys@...rosoft.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] hv_netvsc: Avoid field-overflowing memcpy()

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Add flexible array to represent start of buf_info, improving readability
and avoid future warning where memcpy() thinks it is writing past the
end of the structure.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/net/hyperv/hyperv_net.h   | 1 +
 drivers/net/hyperv/rndis_filter.c | 6 ++----
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index b11aa68b44ec..bc48855dff10 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -1170,6 +1170,7 @@ struct rndis_set_request {
 	u32 info_buflen;
 	u32 info_buf_offset;
 	u32 dev_vc_handle;
+	u8  info_buf[];
 };
 
 /* Response to NdisSetRequest */
diff --git a/drivers/net/hyperv/rndis_filter.c b/drivers/net/hyperv/rndis_filter.c
index 983bf362466a..f6c9c2a670f9 100644
--- a/drivers/net/hyperv/rndis_filter.c
+++ b/drivers/net/hyperv/rndis_filter.c
@@ -1051,10 +1051,8 @@ static int rndis_filter_set_packet_filter(struct rndis_device *dev,
 	set = &request->request_msg.msg.set_req;
 	set->oid = RNDIS_OID_GEN_CURRENT_PACKET_FILTER;
 	set->info_buflen = sizeof(u32);
-	set->info_buf_offset = sizeof(struct rndis_set_request);
-
-	memcpy((void *)(unsigned long)set + sizeof(struct rndis_set_request),
-	       &new_filter, sizeof(u32));
+	set->info_buf_offset = offsetof(typeof(*set), info_buf);
+	memcpy(set->info_buf, &new_filter, sizeof(u32));
 
 	ret = rndis_filter_send_request(dev, request);
 	if (ret == 0) {
-- 
2.30.2