[PATCH] af9035: Add USB read checksumming

[Michael Büsch]

This adds USB message read checksumming to protect against
device and bus errors.
It also adds a read length check to avoid returning garbage from
the buffer, if the device truncated the message.

Signed-off-by: Michael Buesch <m...@bues.ch>

---

Index: linux/drivers/media/dvb/dvb-usb/af9035.c
===================================================================
--- linux.orig/drivers/media/dvb/dvb-usb/af9035.c       2012-04-01 
21:44:27.767000731 +0200
+++ linux/drivers/media/dvb/dvb-usb/af9035.c    2012-04-01 22:26:46.020185359 
+0200
@@ -37,6 +37,22 @@
        }
 };
 
+static u16 af9035_checksum(const u8 *buf, size_t len)
+{
+       size_t i;
+       u16 checksum = 0;
+
+       for (i = 1; i < len; i++) {
+               if (i % 2)
+                       checksum += buf[i] << 8;
+               else
+                       checksum += buf[i];
+       }
+       checksum = ~checksum;
+
+       return checksum;
+}
+
 static int af9035_ctrl_msg(struct usb_device *udev, struct usb_req *req)
 {
 #define BUF_LEN 63
@@ -45,11 +61,11 @@
 #define CHECKSUM_LEN 2
 #define USB_TIMEOUT 2000
 
-       int ret, i, act_len;
+       int ret, act_len;
        u8 buf[BUF_LEN];
        u32 msg_len;
        static u8 seq; /* packet sequence number */
-       u16 checksum = 0;
+       u16 checksum, tmpsum;
 
        /* buffer overflow check */
        if (req->wlen > (BUF_LEN - REQ_HDR_LEN - CHECKSUM_LEN) ||
@@ -70,14 +86,7 @@
                memcpy(&buf[4], req->wbuf, req->wlen);
 
        /* calc and add checksum */
-       for (i = 1; i < buf[0]-1; i++) {
-               if (i % 2)
-                       checksum += buf[i] << 8;
-               else
-                       checksum += buf[i];
-       }
-       checksum = ~checksum;
-
+       checksum = af9035_checksum(buf, buf[0] - 1);
        buf[buf[0]-1] = (checksum >> 8);
        buf[buf[0]-0] = (checksum & 0xff);
 
@@ -107,7 +116,23 @@
                ret = -EIO;
                goto err_mutex_unlock;
        }
+       if (act_len != msg_len) {
+               err("recv bulk message truncated (%d != %u)\n",
+                   act_len, (unsigned int)msg_len);
+               ret = -EIO;
+               goto err_mutex_unlock;
+       }
 
+       /* verify checksum */
+       checksum = af9035_checksum(buf, act_len - 2);
+       tmpsum = (buf[act_len - 2] << 8) | buf[act_len - 1];
+       if (tmpsum != checksum) {
+               err("%s: command=%02X checksum mismatch (%04X != %04X)\n",
+                   __func__, req->cmd,
+                   (unsigned int)tmpsum, (unsigned int)checksum);
+               ret = -EIO;
+               goto err_mutex_unlock;
+       }
        /* check status */
        if (buf[2]) {
                pr_debug("%s: command=%02x failed fw error=%d\n", __func__,


-- 
Greetings, Michael.

PGP encryption is encouraged / 908D8B0E

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