linux-kernel - Re: [PATCH v3 4/4] mtdchar: add MEMREAD ioctl

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Date:   Thu, 3 Feb 2022 10:46:54 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Richard Weinberger <richard@....at>
Cc:     Michał Kępień <kernel@...pniu.pl>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/4] mtdchar: add MEMREAD ioctl

Hi Richard,

richard@....at wrote on Thu, 3 Feb 2022 10:18:56 +0100 (CET):

> Michał,
> 
> ----- Ursprüngliche Mail -----
> > Von: "Michał Kępień" <kernel@...pniu.pl>
> > An: "Miquel Raynal" <miquel.raynal@...tlin.com>, "richard" <richard@....at>, "Vignesh Raghavendra" <vigneshr@...com>
> > CC: "Boris Brezillon" <boris.brezillon@...labora.com>, "linux-mtd" <linux-mtd@...ts.infradead.org>, "linux-kernel"
> > <linux-kernel@...r.kernel.org>
> > Gesendet: Dienstag, 25. Januar 2022 11:48:22
> > Betreff: [PATCH v3 4/4] mtdchar: add MEMREAD ioctl  
> 
> > +	if (req.start + req.len > mtd->size) {  
> 
> I think this can overflow since both req.start and req.len are u64.
> So an evil-doer might bypass this check.
> 
> > +		ret = -EINVAL;
> > +		goto out;
> > +	}
> > +
> > +	datbuf_len = min_t(size_t, req.len, mtd->erasesize);
> > +	if (datbuf_len > 0) {
> > +		datbuf = kmalloc(datbuf_len, GFP_KERNEL);  
> 
> If mtd->erasesize is large (which is not uncommon these days) you might
> request more from kmalloc() than it can serve.
> Maybe kvmalloc() makes more sense?

Mmmh, I would really like these buffers dma-able.

I just discovered mtd_kmalloc_up_to(). Would this work?

> 
> > +		if (!datbuf) {
> > +			ret = -ENOMEM;
> > +			goto out;
> > +		}
> > +	}
> > +
> > +	oobbuf_len = min_t(size_t, req.ooblen, mtd->erasesize);
> > +	if (oobbuf_len > 0) {
> > +		oobbuf = kmalloc(oobbuf_len, GFP_KERNEL);  
> 
> Same.
> 
> Thanks,
> //richard


Thanks,
Miquèl