Date: Tue, 2 Jul 2024 15:32:16 +0200
From: Sascha Hauer <s.hauer@...gutronix.de>
To: Francesco Dolcini <francesco@...cini.it>
Cc: Brian Norris <briannorris@...omium.org>, Kalle Valo <kvalo@...nel.org>,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Lin <yu-hao.lin@....com>
Subject: Re: [PATCH] [RFC] mwifiex: Fix NULL pointer deref

On Mon, Jun 24, 2024 at 06:20:14PM +0200, Francesco Dolcini wrote:
> Hello Sascha,
> 
> On Fri, Jun 21, 2024 at 11:07:27AM +0200, Sascha Hauer wrote:
> > 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;
> 
> The change looks fine to me.
> 
> I am just wondering if this might have anything to do with
> commit a17b9f590f6e ("wifi: mwifiex: Fix interface type change"), maybe you have already looked into it?

It looks somehow related. I just gave it a try and it at least doesn't
fix my issue.

Sascha

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