At the last iteration of the loop, j may equal zero and thus
tp_list[j - 1] causes an invalid read.
Changed the logic of the loop so that j - 1 is always >= 0.

Signed-off-by: Adrien Schildknecht <adrien+...@schischi.me>
---
 net/mac80211/rc80211_minstrel.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 247552a..3ece7d1 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -92,14 +92,15 @@ int minstrel_get_tp_avg(struct minstrel_rate *mr, int 
prob_ewma)
 static inline void
 minstrel_sort_best_tp_rates(struct minstrel_sta_info *mi, int i, u8 *tp_list)
 {
-       int j = MAX_THR_RATES;
-       struct minstrel_rate_stats *tmp_mrs = &mi->r[j - 1].stats;
+       int j;
+       struct minstrel_rate_stats *tmp_mrs;
        struct minstrel_rate_stats *cur_mrs = &mi->r[i].stats;
 
-       while (j > 0 && (minstrel_get_tp_avg(&mi->r[i], cur_mrs->prob_ewma) >
-              minstrel_get_tp_avg(&mi->r[tp_list[j - 1]], 
tmp_mrs->prob_ewma))) {
-               j--;
+       for (j = MAX_THR_RATES; j > 0; --j) {
                tmp_mrs = &mi->r[tp_list[j - 1]].stats;
+               if (minstrel_get_tp_avg(&mi->r[i], cur_mrs->prob_ewma) <=
+                   minstrel_get_tp_avg(&mi->r[tp_list[j - 1]], 
tmp_mrs->prob_ewma))
+                       break;
        }
 
        if (j < MAX_THR_RATES - 1)
-- 
2.4.6

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