On Fri, Feb 24, 2017 at 06:55:02PM +0100, Greg Kroah-Hartman wrote: > On Fri, Feb 24, 2017 at 06:33:04PM +0100, Johan Hovold wrote: > > On Fri, Feb 24, 2017 at 01:38:25PM +0000, Ben Hutchings wrote: > On Fri, 2017-02-24 at 09:25 +0100, Greg Kroah-Hartman wrote: > > > > 4.4-stable review patch. If anyone has any objections, please let me know. > > > > > > > > ------------------ > > > > > > > > From: Johan Hovold <johan@xxxxxxxxxx> > > > > > > > > commit 2d380889215fe20b8523345649dee0579821800c upstream. > > > > > > > > Make sure to check for short transfers to avoid underflow in a loop > > > > condition when parsing the receive buffer. > > > > > > > > Also fix an off-by-one error in the incomplete sanity check which could > > > > lead to invalid data being parsed. > > > > > > This appears to *introduce* an off-by-one. Which is not as serious as > > > the underflow, but is still a regression. > > > > > > Suppose we have urb->actual_length == 4: > > > > > > [...] > > > > - for (i = 0; i < urb->actual_length - 3;) { > > > > > > i < 1 is true, so we would run the loop once. > > > > > > > - opcode = ((unsigned char *)urb->transfer_buffer)[i++]; > > > > - line = ((unsigned char *)urb->transfer_buffer)[i++]; > > > > - status = ((unsigned char *)urb->transfer_buffer)[i++]; > > > > - val = ((unsigned char *)urb->transfer_buffer)[i++]; > > > > + for (i = 0; i < urb->actual_length - 4; i += 4) { > > > > > > i < 0 is false, so we now skip the loop. > > > > Good catch, thanks! The original loop condition was indeed correct > > (modulo the missing underflow check), and I'll post a follow-up fix to > > address this. > > > > > > + opcode = buf[i]; > > > > + line = buf[i + 1]; > > > > + status = buf[i + 2]; > > > > + val = buf[i + 3]; > > > > You should probably not apply this one until after the follow-up is in > > Linus' tree as this patch breaks TIOCMGET. > > Ok, I'll drop this one from the stable tree now. Remind me to pick this > one up when the fixup hits Linus's tree. The follow-up fix is now in Linus's tree so both this one: 2d380889215f ("USB: serial: digi_acceleport: fix OOB data sanity check") and the follow-up: 2e46565cf622 ("USB: serial: digi_acceleport: fix OOB-event processing") can now be applied to the stable trees. Thanks, Johan