linux-hardening - Re: [PATCH RFC] iio: irsd200: fix -Warray-bounds bug in irsd200_trigger

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Date:   Wed, 9 Aug 2023 18:13:29 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        "GONG, Ruiqi" <gongruiqi@...weicloud.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Waqar Hameed <waqar.hameed@...s.com>,
        Kees Cook <keescook@...omium.org>, <linux-iio@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-hardening@...r.kernel.org>,
        Wang Weiyang <wangweiyang2@...wei.com>,
        Xiu Jianfeng <xiujianfeng@...wei.com>, <gongruiqi1@...wei.com>
Subject: Re: [PATCH RFC] iio: irsd200: fix -Warray-bounds bug in
 irsd200_trigger_handler

On Wed, 9 Aug 2023 09:37:29 +0100
Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:

> On Tue, 8 Aug 2023 05:10:04 -0600
> "Gustavo A. R. Silva" <gustavoars@...nel.org> wrote:
> 
> > On Tue, Aug 08, 2023 at 04:37:19PM +0800, GONG, Ruiqi wrote:  
> > > From: "GONG, Ruiqi" <gongruiqi1@...wei.com>
> > > 
> > > When compiling with gcc 13 with -Warray-bounds enabled:
> > > 
> > > In file included from drivers/iio/proximity/irsd200.c:15:
> > > In function ‘iio_push_to_buffers_with_timestamp’,
> > >     inlined from ‘irsd200_trigger_handler’ at drivers/iio/proximity/irsd200.c:770:2:
> > > ./include/linux/iio/buffer.h:42:46: error: array subscript ‘int64_t {aka long long int}[0]’
> > > is partly outside array bounds of ‘s16[1]’ {aka ‘short int[1]’} [-Werror=array-bounds=]
> > >    42 |                 ((int64_t *)data)[ts_offset] = timestamp;
> > >       |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
> > > drivers/iio/proximity/irsd200.c: In function ‘irsd200_trigger_handler’:
> > > drivers/iio/proximity/irsd200.c:763:13: note: object ‘buf’ of size 2
> > >   763 |         s16 buf = 0;
> > >       |             ^~~
> > > 
> > > The problem seems to be that irsd200_trigger_handler() is taking a s16
> > > variable as an int64_t buffer. Fix it by extending the buffer to 64 bits.    
> > 
> > Thanks for working on this!
> >   
> > > 
> > > Link: https://github.com/KSPP/linux/issues/331
> > > Signed-off-by: GONG, Ruiqi <gongruiqi1@...wei.com>    
> > 
> > Acked-by: Gustavo A. R. Silva <gustavoars@...nel.org>  
> 
> Good find on the bug, but the fix is wrong even if it squashes the error.
> 
> > 
> > --
> > Gustavo
> >   
> > > ---
> > > 
> > > RFC: It's a preliminary patch since I'm not familiar with this hardware.
> > > Further comments/reviews are needed about whether this fix is correct,
> > > or we should use iio_push_to_buffers() instead of the *_with_timestamp()
> > > version.
> > > 
> > >  drivers/iio/proximity/irsd200.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/iio/proximity/irsd200.c b/drivers/iio/proximity/irsd200.c
> > > index 5bd791b46d98..34c479881bdf 100644
> > > --- a/drivers/iio/proximity/irsd200.c
> > > +++ b/drivers/iio/proximity/irsd200.c
> > > @@ -759,10 +759,10 @@ static irqreturn_t irsd200_trigger_handler(int irq, void *pollf)
> > >  {
> > >  	struct iio_dev *indio_dev = ((struct iio_poll_func *)pollf)->indio_dev;
> > >  	struct irsd200_data *data = iio_priv(indio_dev);
> > > -	s16 buf = 0;
> > > +	int64_t buf = 0;  
> 
> s64 as internal kernel type.
> More importantly needs to be at least s64 buf[2]; as the offset
> https://elixir.bootlin.com/linux/latest/source/include/linux/iio/buffer.h#L41
> will be 1 due to this filling the timestamp in at first 8 byte aligned location
> after the data that is already in the buffer.
> 
> With hindsight was a bad decision a long time ago not to force people to also
> pass the size into this function so we could detect this at runtime at least.
> Hard to repair now give very large number of drivers using this and the fact
> that it's not always easy to work out that size.  Unfortunately occasionally
> one of these slips through review :(
> 
> I suppose we could, in some cases check if the buffer was at least 16 bytes which
> would get us some of the way.
> 
I was going to pick the patch up and modify it, but I think you managed
to send it out as an html email so it didn't reach the mailing list archives.
If you could send a v2 with s64 buf[2]; that would be great.
Due to some travel I need to send a pull request shortly but this won't be in
a release for some time (as pull is targetting 6.6) so not a problem as long
as we make sure to address in soon.

Thanks,

Jonathan

> Jonathan
> 
> > >  	int ret;
> > >  
> > > -	ret = irsd200_read_data(data, &buf);
> > > +	ret = irsd200_read_data(data, (s16 *)&buf);
> > >  	if (ret)
> > >  		goto end;
> > >  
> > > -- 
> > > 2.41.0
> > >     
>