Re: [PATCH] Fix NR_KEYS off-by-one error

[Andrew Morton <akpm@osdl.org>]

OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> wrote:
>
> Andries Brouwer <aebr@win.tue.nl> writes:
> 
> > On Sat, Jul 17, 2004 at 01:35:59AM +0900, OGAWA Hirofumi wrote:
> > 
> > :: KDGKBENT ioctl can use 256 entries (0-255), but it was defined as
> > :: key_map[NR_KEYS] (NR_KEYS == 255). The code seems also thinking it's 256.
> > :: 
> > :: 	key_map[0] = U(K_ALLOCATED);
> > :: 	for (j = 1; j < NR_KEYS; j++)
> > :: 		key_map[j] = U(K_HOLE);
> > 
> > I think the code has no opinion. It was 128 in 2.4.
> > I am not aware of assumptions on NR_KEYS.
> > So, do not think this is an off-by-one error.
> 
> My point is that key_map is 0-254 array. But KDGKBENT uses 255
> 
> 	case KDGKBENT:
> 		key_map = key_maps[s];
> 		if (key_map) {
> 		    val = U(key_map[i]);
> 		    if (kbd->kbdmode != VC_UNICODE && KTYP(val) >= NR_TYPES)
> 			val = K_HOLE;
> 		} else
> 		    val = (i ? K_HOLE : K_NOSUCHMAP);
> 		return put_user(val, &user_kbe->kb_value);
> 

This all seems a bit inconclusive.  Do we proceed with the original patch
or not?  If not, how do we fix the overflow which Hirofumi has identified?