[patch 003/104] USB: usbmon: fix read(2)

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Pete Zaitcev <zaitcev@xxxxxxxxxx>

commit f1c0a2a3aff53698f4855968d576464041d49b39 upstream.

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 <inguin@xxxxxx>
Signed-off-by: Pete Zaitcev <zaitcev@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 drivers/usb/mon/mon_bin.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- 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 
 	}
 
 	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)

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