mac80211: fix invalid read in minstrel_sort_best_tp_rates()

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

Cc: stable@vger.kernel.org
Signed-off-by: Adrien Schildknecht <adrien+dev@schischi.me>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 247552a7f6c2f23a1e4bc89b647d8d37680bf2c3..3ece7d1034c81ae8749cada074fbebecbe06d57f 100644 (file)
--- 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)