linux-kernel - Re: [PATCH net] Bluetooth: MGMT: Fix OOB access in parse_adv_monitor

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Message-ID: <CABBYNZJLtTiFZ-1LchJ7Cy1JT=vuDmkkRHjrUY92jC740ihs5w@mail.gmail.com>
Date: Thu, 23 Oct 2025 11:30:14 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Ilia Gavrilov <Ilia.Gavrilov@...otecs.ru>
Cc: Marcel Holtmann <marcel@...tmann.org>, Johan Hedberg <johan.hedberg@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	"linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"lvc-project@...uxtesting.org" <lvc-project@...uxtesting.org>, 
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH net] Bluetooth: MGMT: Fix OOB access in parse_adv_monitor_pattern()

Hi Ilia,

On Thu, Oct 23, 2025 at 11:08 AM Ilia Gavrilov
<Ilia.Gavrilov@...otecs.ru> wrote:
>
> Hi, Luiz, thank you for the review.
>
> On 10/23/25 16:18, Luiz Augusto von Dentz wrote:
> > Hi Ilia,
> >
> > On Mon, Oct 20, 2025 at 11:12 AM Ilia Gavrilov
> > <Ilia.Gavrilov@...otecs.ru> wrote:
> >>
> >> In the parse_adv_monitor_pattern() function, the value of
> >> the 'length' variable is currently limited to HCI_MAX_EXT_AD_LENGTH(251).
> >> The size of the 'value' array in the mgmt_adv_pattern structure is 31.
> >> If the value of 'pattern[i].length' is set in the user space
> >> and exceeds 31, the 'patterns[i].value' array can be accessed
> >> out of bound when copied.
> >>
> >> Increasing the size of the 'value' array in
> >> the 'mgmt_adv_pattern' structure will break the userspace.
> >> Considering this, and to avoid OOB access revert the limits for 'offset'
> >> and 'length' back to the value of HCI_MAX_AD_LENGTH.
> >>
> >> Found by InfoTeCS on behalf of Linux Verification Center
> >> (linuxtesting.org) with SVACE.
> >>
> >> Fixes: db08722fc7d4 ("Bluetooth: hci_core: Fix missing instances using HCI_MAX_AD_LENGTH")
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Ilia Gavrilov <Ilia.Gavrilov@...otecs.ru>
> >> ---
> >>  include/net/bluetooth/mgmt.h | 2 +-
> >>  net/bluetooth/mgmt.c         | 6 +++---
> >>  2 files changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/net/bluetooth/mgmt.h b/include/net/bluetooth/mgmt.h
> >> index 74edea06985b..4b07ce6dfd69 100644
> >> --- a/include/net/bluetooth/mgmt.h
> >> +++ b/include/net/bluetooth/mgmt.h
> >> @@ -780,7 +780,7 @@ struct mgmt_adv_pattern {
> >>         __u8 ad_type;
> >>         __u8 offset;
> >>         __u8 length;
> >> -       __u8 value[31];
> >> +       __u8 value[HCI_MAX_AD_LENGTH];
> >
> > Why not use HCI_MAX_EXT_AD_LENGTH above? Or perhaps even make it
> > opaque since the actual size is defined by length - offset.
> >
>
> As I see it, user programs rely on this size of the structure, and if the size is changed, they will be broken.
> Excerpt from bluez tools sources:
> ...
> structure of mgmt_adv_pattern {
> uint8_t ad type;
>         uint8_t offset;
>         length of uint8_t;
>         uint8_t value[31];
> } __packed;
> ...

Well it is broken for EA already, so the question is should we leave
it to just handle legacy advertisement or not? At some point I was
actually just considering removing/deprecating the support of this
command altogether since there exists a standard way to do
advertisement monitoring called Monitoring Advertisers introduced in
6.0:

https://www.bluetooth.com/core-specification-6-feature-overview/?utm_source=internal&utm_medium=blog&utm_campaign=technical&utm_content=now-available-new-version-of-the-bluetooth-core-specification

The the standard monitoring list doesn't seem to be able to do
filtering on the data itself, which I think the where the decision
based filtering used, so it is not really compatible with the MS
vendor commands.

>
> >>  } __packed;
> >>
> >>  #define MGMT_OP_ADD_ADV_PATTERNS_MONITOR       0x0052
> >> diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
> >> index a3d16eece0d2..500033b70a96 100644
> >> --- a/net/bluetooth/mgmt.c
> >> +++ b/net/bluetooth/mgmt.c
> >> @@ -5391,9 +5391,9 @@ static u8 parse_adv_monitor_pattern(struct adv_monitor *m, u8 pattern_count,
> >>         for (i = 0; i < pattern_count; i++) {
> >>                 offset = patterns[i].offset;
> >>                 length = patterns[i].length;
> >> -               if (offset >= HCI_MAX_EXT_AD_LENGTH ||
> >> -                   length > HCI_MAX_EXT_AD_LENGTH ||
> >> -                   (offset + length) > HCI_MAX_EXT_AD_LENGTH)
> >> +               if (offset >= HCI_MAX_AD_LENGTH ||
> >> +                   length > HCI_MAX_AD_LENGTH ||
> >> +                   (offset + length) > HCI_MAX_AD_LENGTH)
> >>                         return MGMT_STATUS_INVALID_PARAMS;
> >>
> >>                 p = kmalloc(sizeof(*p), GFP_KERNEL);
> >> --
> >> 2.39.5
> >
> >
> >
>


-- 
Luiz Augusto von Dentz