linux-kernel - [PATCH] usbmon binary format reader loses synchronization

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Date:	Thu, 13 Nov 2008 13:59:45 +0100
From:	Ingo van Lil <inguin@....de>
To:	Pete Zaitcev <zaitcev@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] usbmon binary format reader loses synchronization

Hello Pete,

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.

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.

Cheers,
Ingo

Signed-off-by: Ingo van Lil <inguin@....de>
---
diff -urN a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c
--- a/drivers/usb/mon/mon_bin.c	2008-07-13 23:51:29.000000000 +0200
+++ b/drivers/usb/mon/mon_bin.c	2008-11-13 11:44:03.000000000 +0100
@@ -681,7 +681,7 @@
 	}

 	if (rp->b_read >= sizeof(struct mon_bin_hdr)) {
-		step_len = min(nbytes, (size_t)ep->len_cap);
+		step_len = min(nbytes, sizeof(struct mon_bin_hdr) + (size_t)ep->len_cap - rp->b_read);
 		offset = rp->b_out + PKT_SIZE;
 		offset += rp->b_read - sizeof(struct mon_bin_hdr);
 		if (offset >= rp->b_size)
--
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