Subject: Re: [PATCH v2] net:qrtr: fix atomic idr allocation in qrtr_port_assign()

From: Manivannan Sadhasivam <[email-masked]>
Date: Mon, 29 Mar 2021 16:39:09 +0530

On Mon, Mar 29, 2021 at 06:55:56PM +0800, Du Cheng wrote:
> On Sun, Mar 28, 2021 at 11:04:17AM +0100, Matthew Wilcox wrote:
> > On Sun, Mar 28, 2021 at 08:56:17AM +0200, Greg Kroah-Hartman wrote:
> > > On Sat, Mar 27, 2021 at 03:51:10PM +0000, Matthew Wilcox wrote:
> > > > On Sat, Mar 27, 2021 at 03:31:18PM +0100, Greg Kroah-Hartman wrote:
> > > > > On Sat, Mar 27, 2021 at 10:25:20PM +0800, Du Cheng wrote:
> > > > > > On Sat, Mar 27, 2021 at 03:12:14PM +0100, Greg Kroah-Hartman wrote:
> > > > > > > Adding the xarray maintainer...
> > > > > > > 
> > > > > > > On Sat, Mar 27, 2021 at 10:07:02PM +0800, Du Cheng wrote:
> > > > > > > > add idr_preload() and idr_preload_end() around idr_alloc_u32(GFP_ATOMIC)
> > > > > > > > due to internal use of per_cpu variables, which requires preemption
> > > > > > > > disabling/enabling.
> > > > > > > > 
> > > > > > > > reported as "BUG: "using smp_processor_id() in preemptible" by syzkaller
> > > > > > > > 
> > > > > > > > Reported-by: [email-masked]
> > > > > > > > Signed-off-by: Du Cheng <[email-masked]>
> > > > > > > > ---
> > > > > > > > changelog
> > > > > > > > v1: change to GFP_KERNEL for idr_alloc_u32() but might sleep
> > > > > > > > v2: revert to GFP_ATOMIC but add preemption disable/enable protection
> > > > > > > > 
> > > > > > > >  net/qrtr/qrtr.c | 6 ++++++
> > > > > > > >  1 file changed, 6 insertions(+)
> > > > > > > > 
> > > > > > > > diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
> > > > > > > > index edb6ac17ceca..6361f169490e 100644
> > > > > > > > --- a/net/qrtr/qrtr.c
> > > > > > > > +++ b/net/qrtr/qrtr.c
> > > > > > > > @@ -722,17 +722,23 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
> > > > > > > >  	mutex_lock(&qrtr_port_lock);
> > > > > > > >  	if (!*port) {
> > > > > > > >  		min_port = QRTR_MIN_EPH_SOCKET;
> > > > > > > > +		idr_preload(GFP_ATOMIC);
> > > > > > > >  		rc = idr_alloc_u32(&qrtr_ports, ipc, &min_port, QRTR_MAX_EPH_SOCKET, GFP_ATOMIC);
> > > > > > > > +		idr_preload_end();
> > > > > > > 

[...]

> > > Ok, it looks like this code is just abandonded, should we remove it
> > > entirely as no one wants to maintain it?
> > 
> > Fine by me.  I don't use it.  Better to get rid of abandonware than keep
> > a potential source of security holes.
> 
> Hi Manivannan,
> 
> For your information.
> 

Thanks for letting me know. I'll look into it once back to work.

Thanks,
Mani

> Regards,
> Du Cheng