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

[Manjunatha Venkatesh]

> -----Original Message-----
> From: Frank Li <frank.li@xxxxxxx>
> Sent: Tuesday, March 25, 2025 8:13 PM
> To: Manjunatha Venkatesh <manjunatha.venkatesh@xxxxxxx>
> Cc: alexandre.belloni@xxxxxxxxxxx; arnd@xxxxxxxx;
> gregkh@xxxxxxxxxxxxxxxxxxx; bbrezillon@xxxxxxxxxx; linux-
> i3c@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> rvmanjumce@xxxxxxxxx; stable@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5] i3c: Fix read from unreadable memory at
> i3c_master_queue_ibi()
> 
> Subject should be
> 
> i3c: Add NULL pointer check in i3c_master_queue_ibi()
> 
[Manjunatha Venkatesh] : I will update the subject line in the next commit.

> 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.
>
[Manjunatha Venkatesh] : This commit message looks better, will use the same in the next commit. 
 
> >
> > Fixes: 3a379bbcea0af ("i3c: Add core I3C infrastructure")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Link:
> > https://lore.kernel.org/lkml/Z9gjGYudiYyl3bSe@lizhi-Precision-Tower-58
> > 10/
> > Signed-off-by: Manjunatha Venkatesh <manjunatha.venkatesh@xxxxxxx>
> > ---
> > 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;
> > +
> >  	atomic_inc(&dev->ibi->pending_ibis);
> >  	queue_work(dev->ibi->wq, &slot->work);  }
> > --
> > 2.46.1
> >