wifi: mac80211: fix memory corruption in minstrel_ht_update_rates()

During our testing of WFM200 module over SDIO on i.MX6Q-based platform,
we discovered a memory corruption on the system, tracing back to the wfx
driver. Using kfence, it was possible to trace it back to the root
cause, which is hw->max_rates set to 8 in wfx_init_common,
while the maximum defined by IEEE80211_TX_TABLE_SIZE is 4.

This causes array out-of-bounds writes during updates of the rate table,
as seen below:

BUG: KFENCE: memory corruption in kfree_rcu_work+0x320/0x36c

Corrupted memory at 0xe0a4ffe0 [ 0x03 0x03 0x03 0x03 0x01 0x00 0x00
0x02 0x02 0x02 0x09 0x00 0x21 0xbb 0xbb 0xbb ] (in kfence-#81):
kfree_rcu_work+0x320/0x36c
process_one_work+0x3ec/0x920
worker_thread+0x60/0x7a4
kthread+0x174/0x1b4
ret_from_fork+0x14/0x2c
0x0

kfence-#81: 0xe0a4ffc0-0xe0a4ffdf, size=32, cache=kmalloc-64

allocated by task 297 on cpu 0 at 631.039555s:
minstrel_ht_update_rates+0x38/0x2b0 [mac80211]
rate_control_tx_status+0xb4/0x148 [mac80211]
ieee80211_tx_status_ext+0x364/0x1030 [mac80211]
ieee80211_tx_status+0xe0/0x118 [mac80211]
ieee80211_tasklet_handler+0xb0/0xe0 [mac80211]
tasklet_action_common.constprop.0+0x11c/0x148
__do_softirq+0x1a4/0x61c
irq_exit+0xcc/0x104
call_with_stack+0x18/0x20
__irq_svc+0x80/0xb0
wq_worker_sleeping+0x10/0x100
wq_worker_sleeping+0x10/0x100
schedule+0x50/0xe0
schedule_timeout+0x2e0/0x474
wait_for_completion+0xdc/0x1ec
mmc_wait_for_req_done+0xc4/0xf8
mmc_io_rw_extended+0x3b4/0x4ec
sdio_io_rw_ext_helper+0x290/0x384
sdio_memcpy_toio+0x30/0x38
wfx_sdio_copy_to_io+0x88/0x108 [wfx]
wfx_data_write+0x88/0x1f0 [wfx]
bh_work+0x1c8/0xcc0 [wfx]
process_one_work+0x3ec/0x920
worker_thread+0x60/0x7a4
kthread+0x174/0x1b4
ret_from_fork+0x14/0x2c 0x0

After discussion on the wireless mailing list it was clarified
that the issue has been introduced by:
commit ee0e16a ("mac80211: minstrel_ht: fill all requested rates")
and fix shall be in minstrel_ht_update_rates in rc80211_minstrel_ht.c.

Fixes: ee0e16a ("mac80211: minstrel_ht: fill all requested rates")
Link: https://lore.kernel.org/all/[email protected]/
Link: https://lore.kernel.org/linux-wireless/[email protected]/
Cc: Jérôme Pouiller <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: Peter Seiderer <[email protected]>
Cc: Kalle Valo <[email protected]>
Cc: Krzysztof Drobiński <[email protected]>,
Signed-off-by: Paweł Lenkow <[email protected]>
Signed-off-by: Lech Perczak <[email protected]>
Reviewed-by: Peter Seiderer <[email protected]>
Reviewed-by: Jérôme Pouiller <[email protected]>
Acked-by: Felix Fietkau <[email protected]>
Signed-off-by: Johannes Berg <[email protected]>

Author: Paweł Lenkow

net/mac80211/rc80211_minstrel_ht.c

@@ -10,6 +10,7 @@
 #include <linux/random.h>
 #include <linux/moduleparam.h>
 #include <linux/ieee80211.h>
+#include <linux/minmax.h>
 #include <net/mac80211.h>
 #include "rate.h"
 #include "sta_info.h"
@@ -1550,6 +1551,7 @@ minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 {
 	struct ieee80211_sta_rates *rates;
 	int i = 0;
+	int max_rates = min_t(int, mp->hw->max_rates, IEEE80211_TX_RATE_TABLE_SIZE);
 
 	rates = kzalloc(sizeof(*rates), GFP_ATOMIC);
 	if (!rates)
@@ -1559,10 +1561,10 @@ minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 	minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_tp_rate[0]);
 
 	/* Fill up remaining, keep one entry for max_probe_rate */
-	for (; i < (mp->hw->max_rates - 1); i++)
+	for (; i < (max_rates - 1); i++)
 		minstrel_ht_set_rate(mp, mi, rates, i, mi->max_tp_rate[i]);
 
-	if (i < mp->hw->max_rates)
+	if (i < max_rates)
 		minstrel_ht_set_rate(mp, mi, rates, i++, mi->max_prob_rate);
 
 	if (i < IEEE80211_TX_RATE_TABLE_SIZE)