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From:   Anant Thazhemadam <anant.thazhemadam@gmail.com>
Cc:     linux-kernel-mentees@lists.linuxfoundation.org,
        Anant Thazhemadam <anant.thazhemadam@gmail.com>,
        syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com,
        Petko Manolov <petkan@nucleusys.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, linux-usb@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [Linux-kernel-mentees][PATCH] rtl8150: set memory to all 0xFFs on failed register reads
Date:   Wed, 16 Sep 2020 10:35:40 +0530
Message-Id: <20200916050540.15290-1-anant.thazhemadam@gmail.com>
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get_registers() copies whatever memory is written by the
usb_control_msg() call even if the underlying urb call ends up failing.

If get_registers() fails, or ends up reading 0 bytes, meaningless and 
junk register values would end up being copied over (and eventually read 
by the driver), and since most of the callers of get_registers() don't 
check the return values of get_registers() either, this would go unnoticed.

It might be a better idea to try and mirror the PCI master abort
termination and set memory to 0xFFs instead in such cases.

Fixes: https://syzkaller.appspot.com/bug?extid=abbc768b560c84d92fd3
Reported-by: syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com
Tested-by: syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
---
 drivers/net/usb/rtl8150.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
index 733f120c852b..04fca7bfcbcb 100644
--- a/drivers/net/usb/rtl8150.c
+++ b/drivers/net/usb/rtl8150.c
@@ -162,8 +162,13 @@ static int get_registers(rtl8150_t * dev, u16 indx, u16 size, void *data)
 	ret = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
 			      RTL8150_REQ_GET_REGS, RTL8150_REQT_READ,
 			      indx, 0, buf, size, 500);
-	if (ret > 0 && ret <= size)
+
+	if (ret < 0)
+		memset(data, 0xff, size);
+
+	else
 		memcpy(data, buf, ret);
+
 	kfree(buf);
 	return ret;
 }
@@ -276,7 +281,7 @@ static int write_mii_word(rtl8150_t * dev, u8 phy, __u8 indx, u16 reg)
 
 static inline void set_ethernet_addr(rtl8150_t * dev)
 {
-	u8 node_id[6];
+	u8 node_id[6] = {0};
 
 	get_registers(dev, IDR, sizeof(node_id), node_id);
 	memcpy(dev->netdev->dev_addr, node_id, sizeof(node_id));
-- 
2.25.1