[EXT] Re: [PATCH v5] i3c: Fix read from unreadable memory at i3c_master_queue_ibi()

[Mukesh Kumar Savaliya]

On 3/26/2025 12:28 PM, Manjunatha Venkatesh wrote:
> 
> 
>> -----Original Message-----
>> From: Mukesh Kumar Savaliya <quic_msavaliy at quicinc.com>
>> Sent: Wednesday, March 26, 2025 12:15 PM
>> To: Frank Li <frank.li at nxp.com>; Manjunatha Venkatesh
>> <manjunatha.venkatesh at nxp.com>
>> Cc: alexandre.belloni at bootlin.com; arnd at arndb.de;
>> gregkh at linuxfoundation.org; bbrezillon at kernel.org; linux-
>> i3c at lists.infradead.org; linux-kernel at vger.kernel.org;
>> rvmanjumce at gmail.com; stable at vger.kernel.org
>> Subject: [EXT] Re: [PATCH v5] i3c: Fix read from unreadable memory at
>> i3c_master_queue_ibi()
>>
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>>
>> On 3/25/2025 8:13 PM, Frank Li wrote:
>>> Subject should be
>>>
>>> i3c: Add NULL pointer check in i3c_master_queue_ibi()
>>>
>> yes, Aligned.
>>> On Tue, Mar 25, 2025 at 03:53:32PM +0530, Manjunatha Venkatesh wrote:
>>>> As part of I3C driver probing sequence for particular device
>>>> instance, While adding to queue it is trying to access ibi variable
>>>> of dev which is not yet initialized causing "Unable to handle kernel
>>>> read from unreadable memory" resulting in kernel panic.
>>>>
>>>> Below is the sequence where this issue happened.
>>>> 1. During boot up sequence IBI is received at host  from the slave device
>>>>      before requesting for IBI, Usually will request IBI by calling
>>>>      i3c_device_request_ibi() during probe of slave driver.
>>>> 2. Since master code trying to access IBI Variable for the particular
>>>>      device instance before actually it initialized by slave driver,
>>>>      due to this randomly accessing the address and causing kernel panic.
>>>> 3. i3c_device_request_ibi() function invoked by the slave driver where
>>>>      dev->ibi = ibi; assigned as part of function call
>>>>      i3c_dev_request_ibi_locked().
>>>> 4. But when IBI request sent by slave device, master code  trying to access
>>>>      this variable before its initialized due to this race condition
>>>>      situation kernel panic happened.
>>>
>>> How about commit message as:
>>>
>>> The I3C master driver may receive an IBI from a target device that has
>>> not been probed yet. In such cases, the master calls
>>> `i3c_master_queue_ibi()` to queue an IBI work task, leading to "Unable
>>> to handle kernel read from unreadable memory" and resulting in a kernel
>> panic.
>>>
>>> Typical IBI handling flow:
>>> 1. The I3C master scans target devices and probes their respective drivers.
>>> 2. The target device driver calls `i3c_device_request_ibi()` to enable IBI
>>>      and assigns `dev->ibi = ibi`.
>>> 3. The I3C master receives an IBI from the target device and calls
>>>      `i3c_master_queue_ibi()` to queue the target device driver's IBI handler
>>>      task.
>>>
>>> However, since target device events are asynchronous to the I3C probe
>>> sequence, step 3 may occur before step 2, causing `dev->ibi` to be
>>> `NULL`, leading to a kernel panic.
>>>
>>> Add a NULL pointer check in `i3c_master_queue_ibi()` to prevent
>>> accessing an uninitialized `dev->ibi`, ensuring stability.
>>>
>>>>
>>>> Fixes: 3a379bbcea0af ("i3c: Add core I3C infrastructure")
>>>> Cc: stable at vger.kernel.org
>>>> Link:
>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flor
>>>> e.kernel.org%2Flkml%2FZ9gjGYudiYyl3bSe%40lizhi-Precision-Tower-
>> 5810%2
>>>>
>> F&data=05%7C02%7Cmanjunatha.venkatesh%40nxp.com%7Ceda8be8c7abc4
>> 3b4ab9
>>>>
>> 608dd6c31c8e7%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C6387
>> 856832
>>>>
>> 77582903%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYi
>> OiIwLjAu
>>>>
>> MDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%
>> 7C%7C
>>>>
>> &sdata=oyc9Wv%2Fj8HMRFIiIGL9nIw0XvI6FsLK2SvsQJ55H7XI%3D&reserved=
>> 0
>>>> Signed-off-by: Manjunatha Venkatesh <manjunatha.venkatesh at nxp.com>
>>>> ---
>>>> Changes since v4:
>>>>     - Fix added at generic places master.c which is applicable for all
>>>> platforms
>>>>
>>>>    drivers/i3c/master.c | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c index
>>>> d5dc4180afbc..c65006aa0684 100644
>>>> --- a/drivers/i3c/master.c
>>>> +++ b/drivers/i3c/master.c
>>>> @@ -2561,6 +2561,9 @@ static void
>> i3c_master_unregister_i3c_devs(struct i3c_master_controller *master)
>>>>     */
>>>>    void i3c_master_queue_ibi(struct i3c_dev_desc *dev, struct i3c_ibi_slot
>> *slot)
>>>>    {
>>>> +    if (!dev->ibi || !slot)
>>>> +            return;
>>>> +
>> 1. Shouldn't this be a Logical AND ? what if slot is non NULL but the IBI is
>> NULL ?
>>
> [Manjunatha Venkatesh] : I think Logical OR operation is correct,
>   Since if any one of the variable is NULL need to return before accessing those variables.
I agree, i was incorrect.
>> 2. This being void function, it doesn't say anything to caller if it's successful or
>> failed ? Should we make this non void function ?
>> if not, i am thinking it may run into multiple attempts, no log too.
> [Manjunatha Venkatesh] : If required we can add error print log, Others please confirm your opinion on this.
>>>>       atomic_inc(&dev->ibi->pending_ibis);
>>>>       queue_work(dev->ibi->wq, &slot->work);
>>>>    }
>>>> --
>>>> 2.46.1
>>>>
>>>
>