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    SubjectRe: [PATCH 3.2 108/221] spi: dw-mid: avoid potential NULL dereference
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    On Wed, 2015-05-06 at 11:25 +0100, Luis Henriques wrote:
    > On Tue, May 05, 2015 at 02:16:39AM +0100, Ben Hutchings wrote:
    > > 3.2.69-rc1 review patch. If anyone has any objections, please let me know.
    > >
    > > ------------------
    > >
    > > From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    > >
    > > commit c9dafb27c84412fe4b17c3b94cc4ffeef5df1833 upstream.
    > >
    > > When DMA descriptor allocation fails we should not try to assign any fields in
    > > the bad descriptor. The patch adds the necessary checks for that.
    > >
    > > Fixes: 7063c0d942a1 (spi/dw_spi: add DMA support)
    > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    > > Signed-off-by: Mark Brown <broonie@kernel.org>
    > > [bwh: Backported to 3.2: adjust context]
    > > Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    > > ---
    > > drivers/spi/spi-dw-mid.c | 6 ++++++
    > > 1 file changed, 6 insertions(+)
    > >
    > > --- a/drivers/spi/spi-dw-mid.c
    > > +++ b/drivers/spi/spi-dw-mid.c
    > > @@ -155,6 +155,9 @@ static int mid_spi_dma_transfer(struct d
    > > 1,
    > > DMA_TO_DEVICE,
    > > DMA_PREP_INTERRUPT | DMA_COMPL_SKIP_DEST_UNMAP);
    > > + if (!txdesc)
    > > + return NULL;
    > > +
    >
    > This backport doesn't look right to me as the function returns an int,
    > not a pointer. OTOH, it seems like this return value is not checked
    > anywhere, which is why I dropped this patch in the 3.16 kernel.

    In mainline the DMA descriptor setup is split out into the
    dw_spi_dma_prepare_tx() and dw_spi_dma_prepare_rx() functions. If they
    return NULL then mid_spi_dma_transfer() doesn't attempt to submit
    adescriptor to the respective channel, but it still returns 0.

    So not only is this backport pretty useless, but so is the upstream
    'fix'.

    Ben.

    > Cheers,
    > --
    > Luís
    >
    > > txdesc->callback = dw_spi_dma_done;
    > > txdesc->callback_param = dws;
    > >
    > > @@ -177,6 +180,9 @@ static int mid_spi_dma_transfer(struct d
    > > 1,
    > > DMA_FROM_DEVICE,
    > > DMA_PREP_INTERRUPT | DMA_COMPL_SKIP_DEST_UNMAP);
    > > + if (!rxdesc)
    > > + return NULL;
    > > +
    > > rxdesc->callback = dw_spi_dma_done;
    > > rxdesc->callback_param = dws;
    > >
    > >
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe stable" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at http://vger.kernel.org/majordomo-info.html

    --
    Ben Hutchings
    If at first you don't succeed, you're doing about average.
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