[PATCH 5.4 121/320] net: mcs7830: handle usb read errors properly

[Greg Kroah-Hartman]

From: Pavel Skripkin <paskripkin@xxxxxxxxx>

[ Upstream commit d668769eb9c52b150753f1653f7f5a0aeb8239d2 ]

Syzbot reported uninit value in mcs7830_bind(). The problem was in
missing validation check for bytes read via usbnet_read_cmd().

usbnet_read_cmd() internally calls usb_control_msg(), that returns
number of bytes read. Code should validate that requested number of bytes
was actually read.

So, this patch adds missing size validation check inside
mcs7830_get_reg() to prevent uninit value bugs

Reported-and-tested-by: syzbot+003c0a286b9af5412510@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 2a36d7083438 ("USB: driver for mcs7830 (aka DeLOCK) USB ethernet adapter")
Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>
Link: https://lore.kernel.org/r/20220106225716.7425-1-paskripkin@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/usb/mcs7830.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/mcs7830.c b/drivers/net/usb/mcs7830.c
index 09bfa6a4dfbc1..7e40e2e2f3723 100644
--- a/drivers/net/usb/mcs7830.c
+++ b/drivers/net/usb/mcs7830.c
@@ -108,8 +108,16 @@ static const char driver_name[] = "MOSCHIP usb-ethernet driver";
 
 static int mcs7830_get_reg(struct usbnet *dev, u16 index, u16 size, void *data)
 {
-	return usbnet_read_cmd(dev, MCS7830_RD_BREQ, MCS7830_RD_BMREQ,
-				0x0000, index, data, size);
+	int ret;
+
+	ret = usbnet_read_cmd(dev, MCS7830_RD_BREQ, MCS7830_RD_BMREQ,
+			      0x0000, index, data, size);
+	if (ret < 0)
+		return ret;
+	else if (ret < size)
+		return -ENODATA;
+
+	return ret;
 }
 
 static int mcs7830_set_reg(struct usbnet *dev, u16 index, u16 size, const void *data)
-- 
2.34.1