[PATCH 12/17] iwlwifi: mvm: don't call << operator with a negative value

[Luca Coelho]

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

In https://bugzilla.kernel.org/show_bug.cgi?id=177341 Bob
reported a UBSAN WARNING on rs.c in iwldvm.
Fix the same bug in iwlmvm.

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.grumb...@intel.com>
Signed-off-by: Luca Coelho <luciano.coe...@intel.com>
---
 drivers/net/wireless/intel/iwlwifi/mvm/rs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/rs.c 
b/drivers/net/wireless/intel/iwlwifi/mvm/rs.c
index 13be9a5b83ee..ce907c58ebf6 100644
--- a/drivers/net/wireless/intel/iwlwifi/mvm/rs.c
+++ b/drivers/net/wireless/intel/iwlwifi/mvm/rs.c
@@ -972,7 +972,9 @@ static u16 rs_get_adjacent_rate(struct iwl_mvm *mvm, 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