linux-kernel - Re: [syzbot] WARNING in __vmalloc_node

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Message-ID: <CACT4Y+bEpri=MaveEOSeGGa3i-hwVgt3Cq13GMQxPLWu7g+ThA@mail.gmail.com>
Date:   Thu, 6 May 2021 17:00:41 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        USB list <linux-usb@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] WARNING in __vmalloc_node_range

On Thu, May 6, 2021 at 4:57 PM Dan Carpenter <dan.carpenter@...cle.com> wrote:
>
> On Thu, May 06, 2021 at 04:22:10PM +0200, Uladzislau Rezki wrote:
> > Seems like vmalloc() is called with zero size passed:
> >
> > <snip>
> > void *__vmalloc_node_range(unsigned long size, unsigned long align,
> >                       unsigned long start, unsigned long end, gfp_t gfp_mask,
> >                       pgprot_t prot, unsigned long vm_flags, int node,
> >                       const void *caller)
> > {
> >       struct vm_struct *area;
> >       void *addr;
> >       unsigned long real_size = size;
> >       unsigned long real_align = align;
> >       unsigned int shift = PAGE_SHIFT;
> >
> > 2873  if (WARN_ON_ONCE(!size))
> >               return NULL;
> > <snip>
> >
> > from the dvb_dmx_init() driver:
> >
> > <snip>
> > int dvb_dmx_init(struct dvb_demux *dvbdemux)
> > {
> >       int i;
> >       struct dmx_demux *dmx = &dvbdemux->dmx;
> >
> >       dvbdemux->cnt_storage = NULL;
> >       dvbdemux->users = 0;
> > 1251  dvbdemux->filter = vmalloc(array_size(sizeof(struct dvb_demux_filter),
> > <snip>                                              dvbdemux->filternum));
>
> Indeed.
>
> It is a mystery because array_size() should never return less than
> sizeof(struct dvb_demux_filter).  That's the whole point of the
> array_size() function is that it returns ULONG_MAX if there is an
> integer overflow.

But it will return 0 if dvbdemux->filternum==0, right?