linux-kernel - Re: [PATCH] [RFC] mwifiex: Fix NULL pointer deref

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Message-ID: <ZnVCzx3-pvbcYQLm@pengutronix.de>
Date: Fri, 21 Jun 2024 11:07:27 +0200
From: Sascha Hauer <s.hauer@...gutronix.de>
To: Brian Norris <briannorris@...omium.org>
Cc: Kalle Valo <kvalo@...nel.org>, linux-wireless@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Lin <yu-hao.lin@....com>,
	Francesco Dolcini <francesco@...cini.it>
Subject: Re: [PATCH] [RFC] mwifiex: Fix NULL pointer deref

On Thu, Jun 20, 2024 at 12:48:01PM -0700, Brian Norris wrote:
> Hi Sascha,
> 
> On Wed, Jun 19, 2024 at 11:05:28AM +0300, Kalle Valo wrote:
> > Sascha Hauer <s.hauer@...gutronix.de> writes:
> > 
> > > When an Access Point is repeatedly started it happens that the
> > > interrupts handler is called with priv->wdev.wiphy being NULL, but
> > > dereferenced in mwifiex_parse_single_response_buf() resulting in:
> > >
> > > | Unable to handle kernel NULL pointer dereference at virtual address 0000000000000140
> ...
> > > | pc : mwifiex_get_cfp+0xd8/0x15c [mwifiex]
> > > | lr : mwifiex_get_cfp+0x34/0x15c [mwifiex]
> > > | sp : ffff8000818b3a70
> > > | x29: ffff8000818b3a70 x28: ffff000006bfd8a5 x27: 0000000000000004
> > > | x26: 000000000000002c x25: 0000000000001511 x24: 0000000002e86bc9
> > > | x23: ffff000006bfd996 x22: 0000000000000004 x21: ffff000007bec000
> > > | x20: 000000000000002c x19: 0000000000000000 x18: 0000000000000000
> > > | x17: 000000040044ffff x16: 00500072b5503510 x15: ccc283740681e517
> > > | x14: 0201000101006d15 x13: 0000000002e8ff43 x12: 002c01000000ffb1
> > > | x11: 0100000000000000 x10: 02e8ff43002c0100 x9 : 0000ffb100100157
> > > | x8 : ffff000003d20000 x7 : 00000000000002f1 x6 : 00000000ffffe124
> > > | x5 : 0000000000000001 x4 : 0000000000000003 x3 : 0000000000000000
> > > | x2 : 0000000000000000 x1 : 0001000000011001 x0 : 0000000000000000
> > > | Call trace:
> > > |  mwifiex_get_cfp+0xd8/0x15c [mwifiex]
> > > |  mwifiex_parse_single_response_buf+0x1d0/0x504 [mwifiex]
> > > |  mwifiex_handle_event_ext_scan_report+0x19c/0x2f8 [mwifiex]
> > > |  mwifiex_process_sta_event+0x298/0xf0c [mwifiex]
> > > |  mwifiex_process_event+0x110/0x238 [mwifiex]
> > > |  mwifiex_main_process+0x428/0xa44 [mwifiex]
> > > |  mwifiex_sdio_interrupt+0x64/0x12c [mwifiex_sdio]
> > > |  process_sdio_pending_irqs+0x64/0x1b8
> > > |  sdio_irq_work+0x4c/0x7c
> > > |  process_one_work+0x148/0x2a0
> > > |  worker_thread+0x2fc/0x40c
> > > |  kthread+0x110/0x114
> > > |  ret_from_fork+0x10/0x20
> > > | Code: a94153f3 a8c37bfd d50323bf d65f03c0 (f940a000)
> > > | ---[ end trace 0000000000000000 ]---
> > >
> > > Fix this by adding a NULL check before dereferencing this pointer.
> > >
> > > Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> > >
> > > ---
> > >
> > > This is the most obvious fix for this problem, but I am not sure if we
> > > might want to catch priv->wdev.wiphy being NULL earlier in the call
> > > chain.
> > 
> > I haven't looked at the call but the symptoms sound like that either we
> > are enabling the interrupts too early or there's some kind of locking
> > problem so that an other cpu doesn't see the change.
> 
> I agree with Kalle that there's a different underlying bug involved, and
> (my conclusion:) we shouldn't whack-a-mole the NULL pointer without
> addressing the underlying problem.
> 
> Looking a bit closer (and without much other context to go on): I believe 
> that one potential underlying problem is the complete lack of locking
> between cfg80211 entry points (such as mwifiex_add_virtual_intf() or
> mwifiex_cfg80211_change_virtual_intf()) and most stuff in the main loop
> (mwifiex_main_process()). The former call sites only hold the wiphy
> lock, and the latter tends to ... mostly not hold any locks, but rely on
> sequentialization with itself, and using its |main_proc_lock| for setup
> and teardown. It's all really bad and ready to fall down like a house of
> cards at any moment. Unfortunately, no one has spent time on
> rearchitecting this driver.
> 
> So it's possible that mwifiex_process_event() (mwifiex_get_priv_by_id()
> / mwifiex_get_priv()) is getting a hold of a not-fully-initialized
> 'priv' structure.
> 
> BTW, in case I can reproduce and poke at your scenario, what exactly
> is your test case? Are you just starting / killing / restarting hostapd
> in a loop?

I am running plain wpa_supplicant -i mlan0 with this config:

network={
        ssid="somessid"
        mode=2
        frequency=2412
        key_mgmt=WPA-PSK WPA-PSK-SHA256
        proto=RSN
        group=CCMP
        pairwise=CCMP
        psk="12345678"
}

wait for the AP to be established, <ctrl-c> wpa_supplicant and start it
again.

It doesn't seem to be a locking problem, see the patch below which fixes
my problem. At some point during incoming events the correct adapter->priv[]
is selected based on bss_num and bss_type. when adapter->priv[0] is used
for AP mode then an incoming event with type MWIFIEX_BSS_TYPE_STA leads
to adapter->priv[1] being picked which is unused and doesn't have a
wiphy attached to it.

Sascha

-------------------------8<----------------------------

>From 3357963821294ff7de26259a154a1cb5bab760cb Mon Sep 17 00:00:00 2001
From: Sascha Hauer <s.hauer@...gutronix.de>
Date: Tue, 18 Jun 2024 12:20:20 +0200
Subject: [PATCH] mwifiex: Do not return unused priv in
 mwifiex_get_priv_by_id()

mwifiex_get_priv_by_id() returns the priv pointer corresponding to the
bss_num and bss_type, but without checking if the priv is actually
currently in use.
Unused priv pointers do not have a wiphy attached to them which can lead
to NULL pointer dereferences further down the callstack.
Fix this by returning only used priv pointers which have priv->bss_mode
set to something else than NL80211_IFTYPE_UNSPECIFIED.

Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
---
 drivers/net/wireless/marvell/mwifiex/main.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/wireless/marvell/mwifiex/main.h b/drivers/net/wireless/marvell/mwifiex/main.h
index 175882485a195..c5164ae41b547 100644
--- a/drivers/net/wireless/marvell/mwifiex/main.h
+++ b/drivers/net/wireless/marvell/mwifiex/main.h
@@ -1287,6 +1287,9 @@ mwifiex_get_priv_by_id(struct mwifiex_adapter *adapter,
 
 	for (i = 0; i < adapter->priv_num; i++) {
 		if (adapter->priv[i]) {
+			if (adapter->priv[i]->bss_mode == NL80211_IFTYPE_UNSPECIFIED)
+				continue;
+
 			if ((adapter->priv[i]->bss_num == bss_num) &&
 			    (adapter->priv[i]->bss_type == bss_type))
 				break;
-- 
2.39.2



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