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

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Message-ID: <19f34b57-a7b7-41e5-8c6c-9e99d7607032@infotecs.ru>
Date: Fri, 24 Oct 2025 08:56:50 +0000
From: Ilia Gavrilov <Ilia.Gavrilov@...otecs.ru>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
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()

On 10/23/25 18:30, Luiz Augusto von Dentz wrote:
> 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? 

From a security point of view, it is better to fix the problem of OOB access of the 'value' array
in all kernels starting from version 6.6+.

There are two solutions: 
1) The simplest solution. Increase the size to the 'value' array in the 'mgmt_adv_pattern' structure,
but this type of command will not work:

$btmgmt
$menu monitor
$add-pattern 16:0:01020304050607080900

2) Do as suggested in this patch

 
> 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
> 

It seems to me that it's better to remove/deprecate the support of the command
in the next version of the kernel.

> 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
>>>
>>>
>>>
>>
> 
>