iwlwifi: mvm: don't call << operator with a negative value

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.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

1 files changed, 3 insertions, 1 deletions

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;