[PATCH] net: mac80211: cfg: enforce sanity checks for key_index in ieee80211_del_key()

[Anant Thazhemadam]

Currently, it is assumed that key_idx values that are passed to
ieee80211_del_key() are all valid indexes as is, and no sanity checks
are performed for it.
However, syzbot was able to trigger an array-index-out-of-bounds bug
by passing a key_idx value of 5, when the maximum permissible index
value is (NUM_DEFAULT_KEYS - 1).
Enforcing sanity checks helps in preventing this bug, or a similar
instance in the context of ieee80211_del_key() from occurring.

Reported-by: syzbot+49d4cab497c2142ee...@syzkaller.appspotmail.com
Tested-by: syzbot+49d4cab497c2142ee...@syzkaller.appspotmail.com
Signed-off-by: Anant Thazhemadam <anant.thazhema...@gmail.com>
---
 net/mac80211/cfg.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 7276e66ae435..d349e33134e6 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -516,12 +516,30 @@ static int ieee80211_del_key(struct wiphy *wiphy, struct 
net_device *dev,
                if (!sta)
                        goto out_unlock;
 
-               if (pairwise)
+               if (pairwise) {
+                       if (key_idx >= NUM_DEFAULT_KEYS) {
+                               ret = -EINVAL;
+                               goto out_unlock;
+                       }
                        key = key_mtx_dereference(local, sta->ptk[key_idx]);
-               else
+               } else {
+                       if (key_idx >= (NUM_DEFAULT_KEYS +
+                                       NUM_DEFAULT_MGMT_KEYS +
+                                       NUM_DEFAULT_BEACON_KEYS)) {
+                               ret = -EINVAL;
+                               goto out_unlock;
+                       }
                        key = key_mtx_dereference(local, sta->gtk[key_idx]);
-       } else
+               }
+       } else {
+               if (key_idx >= (NUM_DEFAULT_KEYS +
+                               NUM_DEFAULT_MGMT_KEYS +
+                               NUM_DEFAULT_BEACON_KEYS)) {
+                       ret = -EINVAL;
+                       goto out_unlock;
+               }
                key = key_mtx_dereference(local, sdata->keys[key_idx]);
+       }
 
        if (!key) {
                ret = -ENOENT;
-- 
2.25.1