net: mcs7830: handle usb read errors properly

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@syzkaller.appspotmail.com
Fixes: 3d0d3c45ebe4 ("USB: driver for mcs7830 (aka DeLOCK) USB ethernet adapter")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20220106225716.7425-1-paskripkin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/usb/mcs7830.c b/drivers/net/usb/mcs7830.c
index 326cc4e749d804d45e186a12b0838ca868943962..fdda0616704eae350553af5ef212b4b234da0bf5 100644 (file)
--- 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)