[PATCH 11/17] iwlwifi: dvm: don't call << operator with a negative value

[Luca Coelho <luca@coelho.fi>]

From: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

In https://bugzilla.kernel.org/show_bug.cgi?id=177341 Bob
reported a UBSAN WARNING on rs.c.

Undefined behaviour in drivers/net/wireless/intel/iwlwifi/dvm/rs.c:746:18

This because
	i = index - 1;
	for (mask = (1 << i); i >= 0; i--, mask >>= 1)

is unsafe: i could be negative and hence we can call <<
on a negative value.
This bug doesn't have any real impact since the condition
of the for loop will prevent any usage of mask.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=177341
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
---
 drivers/net/wireless/intel/iwlwifi/dvm/rs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/dvm/rs.c b/drivers/net/wireless/intel/iwlwifi/dvm/rs.c
index 710dbbefd551..ff44ebc5829d 100644
--- a/drivers/net/wireless/intel/iwlwifi/dvm/rs.c
+++ b/drivers/net/wireless/intel/iwlwifi/dvm/rs.c
@@ -740,7 +740,10 @@ static u16 rs_get_adjacent_rate(struct iwl_priv *priv, u8 index, u16 rate_mask,
 
 		/* Find the previous rate that is in the rate mask */
 		i = index - 1;
-		for (mask = (1 << i); i >= 0; i--, mask >>= 1) {
+		if (i >= 0)
+			mask = BIT(i);
+
+		for (; i >= 0; i--, mask >>= 1) {
 			if (rate_mask & mask) {
 				low = i;
 				break;
-- 
2.11.0