mac80211: fix use of uninitialised values in RX aggregation

Use kzalloc instead of kmalloc for struct tid_ampdu_rx to
initialize the "removed" field (all others are initialized
manually). That fixes:

UBSAN: Undefined behaviour in net/mac80211/rx.c:932:29
load of value 2 is not a valid value for type '_Bool'
CPU: 3 PID: 1134 Comm: kworker/u16:7 Not tainted 4.5.0-rc1+ #265
Workqueue: phy0 rt2x00usb_work_rxdone
 0000000000000004 ffff880254a7ba50 ffffffff8181d866 0000000000000007
 ffff880254a7ba78 ffff880254a7ba68 ffffffff8188422d ffffffff8379b500
 ffff880254a7bab8 ffffffff81884747 0000000000000202 0000000348620032
Call Trace:
 [<ffffffff8181d866>] dump_stack+0x45/0x5f
 [<ffffffff8188422d>] ubsan_epilogue+0xd/0x40
 [<ffffffff81884747>] __ubsan_handle_load_invalid_value+0x67/0x70
 [<ffffffff82227b4d>] ieee80211_sta_reorder_release.isra.16+0x5ed/0x730
 [<ffffffff8222ca14>] ieee80211_prepare_and_rx_handle+0xd04/0x1c00
 [<ffffffff8222db03>] __ieee80211_rx_handle_packet+0x1f3/0x750
 [<ffffffff8222e4a7>] ieee80211_rx_napi+0x447/0x990

While at it, convert to use sizeof(*tid_agg_rx) instead.

Fixes: 788211d8 ("mac80211: fix RX A-MPDU session reorder timer deletion")
Cc: stable@vger.kernel.org
Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
[reword commit message, use sizeof(*tid_agg_rx)]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/agg-rx.c

@@ -291,7 +291,7 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 	}
 
 	/* prepare A-MPDU MLME for Rx aggregation */
-	tid_agg_rx = kmalloc(sizeof(struct tid_ampdu_rx), GFP_KERNEL);
+	tid_agg_rx = kzalloc(sizeof(*tid_agg_rx), GFP_KERNEL);
 	if (!tid_agg_rx)
 		goto end;