mac80211: validate cipher scheme PN length better

Currently, a cipher scheme can advertise an arbitrarily long
sequence counter, but mac80211 only supports up to 16 bytes
and the initial value from userspace will be truncated.

Fix two things:
 * don't allow the driver to register anything longer than
   the 16 bytes that mac80211 reserves space for
 * require userspace to specify a starting value with the
   correct length (or none at all)
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/key.c

@@ -485,15 +485,17 @@ ieee80211_key_alloc(u32 cipher, int idx, size_t key_len,
 		break;
 	default:
 		if (cs) {
-			size_t len = (seq_len > IEEE80211_MAX_PN_LEN) ?
-						IEEE80211_MAX_PN_LEN : seq_len;
+			if (seq_len && seq_len != cs->pn_len) {
+				kfree(key);
+				return ERR_PTR(-EINVAL);
+			}
 
 			key->conf.iv_len = cs->hdr_len;
 			key->conf.icv_len = cs->mic_len;
 			for (i = 0; i < IEEE80211_NUM_TIDS + 1; i++)
-				for (j = 0; j < len; j++)
+				for (j = 0; j < seq_len; j++)
 					key->u.gen.rx_pn[i][j] =
-							seq[len - j - 1];
+							seq[seq_len - j - 1];
 			key->flags |= KEY_FLAG_CIPHER_SCHEME;
 		}
 	}

net/mac80211/main.c

@@ -768,8 +768,11 @@ static int ieee80211_init_cipher_suites(struct ieee80211_local *local)
 			suites[w++] = WLAN_CIPHER_SUITE_BIP_GMAC_256;
 		}
 
-		for (r = 0; r < local->hw.n_cipher_schemes; r++)
+		for (r = 0; r < local->hw.n_cipher_schemes; r++) {
 			suites[w++] = cs[r].cipher;
+			if (WARN_ON(cs[r].pn_len > IEEE80211_MAX_PN_LEN))
+				return -EINVAL;
+		}
 	}
 
 	local->hw.wiphy->cipher_suites = suites;