Re: [PATCH] misc: fastrpc: Fix NULL pointer dereference in rpmsg callback

[Mukesh Ojha]

On Sat, Apr 18, 2026 at 01:35:00AM +0300, Dmitry Baryshkov wrote:
> On Sat, Apr 18, 2026 at 01:31:46AM +0530, Mukesh Ojha wrote:
> > A NULL pointer dereference was observed on Hawi at boot when the DSP
> > sends a glink message before fastrpc_rpmsg_probe() has completed
> > initialization:
> > 
> >   Unable to handle kernel NULL pointer dereference at virtual address 0000000000000178
> >   pc : _raw_spin_lock_irqsave+0x34/0x8c
> >   lr : fastrpc_rpmsg_callback+0x3c/0xcc [fastrpc]
> >   ...
> >   Call trace:
> >    _raw_spin_lock_irqsave+0x34/0x8c (P)
> >    fastrpc_rpmsg_callback+0x3c/0xcc [fastrpc]
> >    qcom_glink_native_rx+0x538/0x6a4
> >    qcom_glink_smem_intr+0x14/0x24 [qcom_glink_smem]
> > 
> > The faulting address 0x178 corresponds to the lock variable inside
> > struct fastrpc_channel_ctx, confirming that cctx is NULL when
> > fastrpc_rpmsg_callback() attempts to take the spinlock.
> > 
> > There are two issues here. First, dev_set_drvdata() is called before
> > spin_lock_init() and idr_init(), leaving a window where the callback
> > can retrieve a valid cctx pointer but operate on an uninitialized
> > spinlock. Second, the rpmsg channel becomes live as soon as the driver
> > is bound, so fastrpc_rpmsg_callback() can fire before dev_set_drvdata()
> > is called at all, resulting in dev_get_drvdata() returning NULL.
> > 
> > Fix both issues by moving all cctx initialization ahead of
> > dev_set_drvdata() so the structure is fully initialized before it
> > becomes visible to the callback, and add a NULL check in
> > fastrpc_rpmsg_callback() as a guard against any remaining window.
> > 
> > Signed-off-by: Mukesh Ojha <mukesh.ojha@xxxxxxxxxxxxxxxx>
> 
> Missing Fixes / cc:stable. Otherwise LGTM.

Will add in v2.

> 
> As a side note, we really should rewrite that part into loop over
> subnodes instead of the of_populate and depending on subdevices to
> probe.
> 

I get your point and worked on removing of_populate and removeing
probe/remove  while it can be simple init call from the parent probe.
Let me refactor it.

> -- 
> With best wishes
> Dmitry

-- 
-Mukesh Ojha