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tty/vt/keyboard: fix OOB access in do_compute_shiftstate()

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The size of individual keymap in drivers/tty/vt/keyboard.c is NR_KEYS,
which is currently 256, whereas number of keys/buttons in input device (and
therefor in key_down) is much larger - KEY_CNT - 768, and that can cause
out-of-bound access when we do

	sym = U(key_maps[0][k]);

with large 'k'.

To fix it we should not attempt iterating beyond smaller of NR_KEYS and
KEY_CNT.

Also while at it let's switch to for_each_set_bit() instead of open-coding
it.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
This commit is contained in:
Dmitry Torokhov 2016-06-27 14:12:34 -07:00
parent e4add7b6be
commit 510cccb5b0
1 changed files with 9 additions and 21 deletions
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30
drivers/tty/vt/keyboard.c
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@ -366,34 +366,22 @@ static void to_utf8(struct vc_data *vc, uint c)
static void do_compute_shiftstate(void)
{
unsigned int i, j, k, sym, val;
unsigned int k, sym, val;
shift_state = 0;
memset(shift_down, 0, sizeof(shift_down));
for (i = 0; i < ARRAY_SIZE(key_down); i++) {
if (!key_down[i])
for_each_set_bit(k, key_down, min(NR_KEYS, KEY_CNT)) {
sym = U(key_maps[0][k]);
if (KTYP(sym) != KT_SHIFT && KTYP(sym) != KT_SLOCK)
continue;
k = i * BITS_PER_LONG;
val = KVAL(sym);
if (val == KVAL(K_CAPSSHIFT))
val = KVAL(K_SHIFT);
for (j = 0; j < BITS_PER_LONG; j++, k++) {
if (!test_bit(k, key_down))
continue;
sym = U(key_maps[0][k]);
if (KTYP(sym) != KT_SHIFT && KTYP(sym) != KT_SLOCK)
continue;
val = KVAL(sym);
if (val == KVAL(K_CAPSSHIFT))
val = KVAL(K_SHIFT);
shift_down[val]++;
shift_state |= (1 << val);
}
shift_down[val]++;
shift_state |= BIT(val);
}
}