[PATCH] mtd: nand: pxa3xx: Fix buffer overflow during raw reads

[Michael Nazzareno Trimarchi]

Hi Chris

On Sun, Jul 30, 2023 at 11:21 PM Chris Packham <judge.packham at gmail.com> wrote:
>
> Hi Pierre,
>
> On Sun, Jul 30, 2023 at 6:08 AM Pierre Bourdon <delroth at gmail.com> wrote:
> >
> > Chunked raw reads get accumulated to the data buffer, but in some
> > ECC configurations they can end up being larger than the originally
> > computed size (write page size + OOB size). For example:
> >
> > 4K page size, ECC strength 8:
> > - Normal reads: writesize (4096B) + oobsize (128B) = 4224 bytes.
> > - Chunked raw reads: 4 chunks of 1024B + 1 final spare area of 64B + 5
> >   ECC areas of 32B = 4320B.
>
> I'm not a NAND expert and I haven't sat down and fully grasped the
> math but I was curious to see what the Linux kernel did. It looks like
> it uses the same mtd->writesize + mtd->oobsize calculation (see
> nand_scan_tail() in nand_base.c). So either Linux has the same bug or
> maybe there's something off in u-boot's nfc_layouts[]. I'll see if I
> can get one of my boards to trigger a KASAN report (I'm not sure if
> any of the NAND chips we use will hit the cases you're pointing out).
>

I have already seen the code about it and this buffer is used only by
uboot to get the result on fake interrupt implementation. The problem
that I have seem is why buf_count is not affected on this change. Is possible
to have a trace down on what happen with more info?

MIchael

> >
> > Fixes: 6293b0361d9 ("mtd: nand: pxa3xx: add raw read support")
> > Signed-off-by: Pierre Bourdon <delroth at gmail.com>
> > ---
> >
> >  drivers/mtd/nand/raw/pxa3xx_nand.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mtd/nand/raw/pxa3xx_nand.c b/drivers/mtd/nand/raw/pxa3xx_nand.c
> > index d502e967f9..2894ababbe 100644
> > --- a/drivers/mtd/nand/raw/pxa3xx_nand.c
> > +++ b/drivers/mtd/nand/raw/pxa3xx_nand.c
> > @@ -1471,6 +1471,19 @@ static void pxa3xx_nand_detect_config(struct pxa3xx_nand_info *info)
> >
> >  static int pxa3xx_nand_init_buff(struct pxa3xx_nand_info *info)
> >  {
> > +       unsigned int chunk_size;
> > +       unsigned int last_chunk_size;
> > +
> > +       /*
> > +        * The data buffer needs to not only be large enough for normal + OOB
> > +        * reads, but also for raw reads. The raw reads can end up taking more
> > +        * space due to the chunking scheme.
> > +        */
> > +       chunk_size = info->chunk_size + info->spare_size + info->ecc_size;
> > +       last_chunk_size =
> > +               info->last_chunk_size + info->last_spare_size + info->ecc_size;
> > +       info->buf_size = info->nfullchunks * chunk_size + last_chunk_size;
> > +
> >         info->data_buff = kmalloc(info->buf_size, GFP_KERNEL);
> >         if (info->data_buff == NULL)
> >                 return -ENOMEM;
> > @@ -1661,7 +1674,6 @@ static int pxa3xx_nand_scan(struct mtd_info *mtd)
> >         kfree(info->data_buff);
> >
> >         /* allocate the real data + oob buffer */
> > -       info->buf_size = mtd->writesize + mtd->oobsize;
> >         ret = pxa3xx_nand_init_buff(info);
> >         if (ret)
> >                 return ret;
> > --
> > 2.41.0
> >



-- 
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael at amarulasolutions.com
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