USB: usbmon: fix read(2)

There's a bug in the usbmon binary reader: When using read() to fetch the packets and a packet's data is partially read, the next read call will once again return up to len_cap bytes of data. The b_read counter is not regarded when determining the remaining chunk size. So, when dumping USB data with "cat /dev/usbmon0 > usbmon.trace" while reading from a USB storage device and analyzing the dump file afterwards it will get out of sync after a couple of packets. Signed-off-by: Ingo van Lil <[email protected]> Signed-off-by: Pete Zaitcev <[email protected]> Cc: stable <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
chewitt · Nov 20, 2008 · f1c0a2a · f1c0a2a
1 parent ff34950
commit f1c0a2a
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c
@@ -687,7 +687,10 @@ static ssize_t mon_bin_read(struct file *file, char __user *buf,
 	}
 
 	if (rp->b_read >= sizeof(struct mon_bin_hdr)) {
-		step_len = min(nbytes, (size_t)ep->len_cap);
+		step_len = ep->len_cap;
+		step_len -= rp->b_read - sizeof(struct mon_bin_hdr);
+		if (step_len > nbytes)
+			step_len = nbytes;
 		offset = rp->b_out + PKT_SIZE;
 		offset += rp->b_read - sizeof(struct mon_bin_hdr);
 		if (offset >= rp->b_size)