USB: serial: digi_acceleport: fix OOB-event processing

commit 2e46565cf622dd0534a9d8bffe152a577b48d7aa upstream.

A recent change claimed to fix an off-by-one error in the OOB-port
completion handler, but instead introduced such an error. This could
specifically led to modem-status changes going unnoticed, effectively
breaking TIOCMGET.

Note that the offending commit fixes a loop-condition underflow and is
marked for stable, but should not be backported without this fix.

Reported-by: Ben Hutchings <ben@decadent.org.uk>
Fixes: 2d380889215f ("USB: serial: digi_acceleport: fix OOB data sanity
check")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/drivers/usb/serial/digi_acceleport.c b/drivers/usb/serial/digi_acceleport.c
index 15b9cb30bb5086fa56ce6a009abfb07cb50d9a83..e8d7c1beae83b6223d71b9ef856da64ffe000699 100644 (file)
--- a/drivers/usb/serial/digi_acceleport.c
+++ b/drivers/usb/serial/digi_acceleport.c
@@ -1498,7 +1498,7 @@ static int digi_read_oob_callback(struct urb *urb)
                return -1;
 
        /* handle each oob command */
-       for (i = 0; i < urb->actual_length - 4; i += 4) {
+       for (i = 0; i < urb->actual_length - 3; i += 4) {
                opcode = buf[i];
                line = buf[i + 1];
                status = buf[i + 2];