[lvc-project] [PATCH net] Bluetooth: MGMT: Fix OOB access in parse_adv_monitor_pattern()

[Ilia Gavrilov]

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 at infotecs.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 at vger.kernel.org
>> Signed-off-by: Ilia Gavrilov <Ilia.Gavrilov at infotecs.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;
...


>>  } __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
> 
> 
>