linux-kernel - Re: [PATCH] udmabuf: validate ubuf->pagecount

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Message-ID: <YeGrgs+4PXM2ud+n@phenom.ffwll.local>
Date:   Fri, 14 Jan 2022 17:57:38 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     kraxel@...hat.com, sumit.semwal@...aro.org,
        christian.koenig@....com, daniel.vetter@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        syzbot+2c56b725ec547fa9cb29@...kaller.appspotmail.com
Subject: Re: [PATCH] udmabuf: validate ubuf->pagecount

On Wed, Jan 12, 2022 at 09:08:46PM +0300, Pavel Skripkin wrote:
> On 12/30/21 17:26, Pavel Skripkin wrote:
> > Syzbot has reported GPF in sg_alloc_append_table_from_pages(). The
> > problem was in ubuf->pages == ZERO_PTR.
> > 
> > ubuf->pagecount is calculated from arguments passed from user-space. If
> > user creates udmabuf with list.size == 0 then ubuf->pagecount will be
> > also equal to zero; it causes kmalloc_array() to return ZERO_PTR.
> > 
> > Fix it by validating ubuf->pagecount before passing it to
> > kmalloc_array().
> > 
> > Fixes: fbb0de795078 ("Add udmabuf misc device")
> > Reported-and-tested-by: syzbot+2c56b725ec547fa9cb29@...kaller.appspotmail.com
> > Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
> > ---
> > 
> 
> Gentle ping :)

Gerd Hoffmann should pick this one up, pls holler again if it doesn't
happen.
-Daniel

> 
> > 
> > ---
> >   drivers/dma-buf/udmabuf.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> > index c57a609db75b..e7330684d3b8 100644
> > --- a/drivers/dma-buf/udmabuf.c
> > +++ b/drivers/dma-buf/udmabuf.c
> > @@ -190,6 +190,10 @@ static long udmabuf_create(struct miscdevice *device,
> >   		if (ubuf->pagecount > pglimit)
> >   			goto err;
> >   	}
> > +
> > +	if (!ubuf->pagecount)
> > +		goto err;
> > +
> >   	ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(*ubuf->pages),
> >   				    GFP_KERNEL);
> >   	if (!ubuf->pages) {
> 
> With regards,
> Pavel Skripkin

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch