mac80211: minstrel_ht: fix a crash in rate sorting

The commit 5935839ad73583781b8bbe8d91412f6826e218a4
"mac80211: improve minstrel_ht rate sorting by throughput & probability"

introduced a crash on rate sorting that occurs when the rate added to
the sorting array is faster than all the previous rates. Due to an
off-by-one error, it reads the rate index from tp_list[-1], which
contains uninitialized stack garbage, and then uses the resulting index
for accessing the group rate stats, leading to a crash if the garbage
value is big enough.

Cc: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
Reported-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 6 insertions, 9 deletions

diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index df90ce2db00c..408fd8ab4eef 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -252,19 +252,16 @@ minstrel_ht_sort_best_tp_rates(struct minstrel_ht_sta *mi, u8 index,
         cur_thr = mi->groups[cur_group].rates[cur_idx].cur_tp;
         cur_prob = mi->groups[cur_group].rates[cur_idx].probability;
 
-        tmp_group = tp_list[j - 1] / MCS_GROUP_RATES;
-        tmp_idx = tp_list[j - 1] % MCS_GROUP_RATES;
-        tmp_thr = mi->groups[tmp_group].rates[tmp_idx].cur_tp;
-        tmp_prob = mi->groups[tmp_group].rates[tmp_idx].probability;
-
-        while (j > 0 && (cur_thr > tmp_thr ||
-              (cur_thr == tmp_thr && cur_prob > tmp_prob))) {
-                j--;
+        do {
                 tmp_group = tp_list[j - 1] / MCS_GROUP_RATES;
                 tmp_idx = tp_list[j - 1] % MCS_GROUP_RATES;
                 tmp_thr = mi->groups[tmp_group].rates[tmp_idx].cur_tp;
                 tmp_prob = mi->groups[tmp_group].rates[tmp_idx].probability;
-        }
+                if (cur_thr < tmp_thr ||
+                    (cur_thr == tmp_thr && cur_prob <= tmp_prob))
+                        break;
+                j--;
+        } while (j > 0);
 
         if (j < MAX_THR_RATES - 1) {
                 memmove(&tp_list[j + 1], &tp_list[j], (sizeof(*tp_list) *