HID: mcp2221: prevent a buffer overflow in mcp_smbus_write()

Smatch Warning:
drivers/hid/hid-mcp2221.c:388 mcp_smbus_write() error: __memcpy()
'&mcp->txbuf[5]' too small (59 vs 255)
drivers/hid/hid-mcp2221.c:388 mcp_smbus_write() error: __memcpy() 'buf'
too small (34 vs 255)

The 'len' variable can take a value between 0-255 as it can come from
data->block[0] and it is user data. So add an bound check to prevent a
buffer overflow in memcpy().

Fixes: 2b1bbc22f0f8 ("HID: mcp2221: add usb to i2c-smbus host bridge")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
index 4211b9839209b147b3c0fb44a7944f1f768ffc1d..de52e9f7bb8cbd26cc7ccefec6bcf3128f923bfd 100644 (file)
--- a/drivers/hid/hid-mcp2221.c
+++ b/drivers/hid/hid-mcp2221.c
@@ -385,6 +385,9 @@ static int mcp_smbus_write(struct mcp2221 *mcp, u16 addr,
                data_len = 7;
                break;
        default:
+               if (len > I2C_SMBUS_BLOCK_MAX)
+                       return -EINVAL;
+
                memcpy(&mcp->txbuf[5], buf, len);
                data_len = len + 5;
        }