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Subject[PATCH 3.16 099/346] tty/vt/keyboard: fix OOB access in do_compute_shiftstate()
3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dmitry Torokhov <dmitry.torokhov@gmail.com>

commit 510cccb5b0c8868a2b302a0ab524da7912da648b upstream.

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>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/tty/vt/keyboard.c | 30 +++++++++---------------------
1 file changed, 9 insertions(+), 21 deletions(-)

--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -365,34 +365,22 @@ static void to_utf8(struct vc_data *vc,

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;
-
- 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);
+ 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);
}
}

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