On Tue, Dec 04, 2018 at 02:11:33PM +0000, Peter Rosin wrote:
> Ho hmm. Had another look at this patch, or rather, the context of the
> patch so not really related, but...
>
> On 2018-12-01 11:01, Nicholas Mc Guire wrote:
> > devm_kstrdup() may return NULL if internal allocation failed.
> > Thus using name, value is unsafe without being checked. As
> > i2c_demux_pinctrl_probe() can return -ENOMEM in other cases
> > a dev_err() message is included to make the failure location
> > clear.
> >
> > Signed-off-by: Nicholas Mc Guire <hofrat@xxxxxxxxx>
> > Fixes: e35478eac030 ("i2c: mux: demux-pinctrl: run properly with multiple instances")
> > ---
> >
> > Problem located with experimental coccinelle script
> >
> > Q: The use of devm_kstrdup() seems a bit odd while technically not wrong,
> > personally I think devm_kasprintf() would be more suitable here.
> >
> > Patch was compile tested with: multi_v7_defconfig
> > (implies I2C_DEMUX_PINCTRL=y)
> >
> > Patch is against 4.20-rc4 (localversion-next is next-20181130)
> >
> > drivers/i2c/muxes/i2c-demux-pinctrl.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/i2c/muxes/i2c-demux-pinctrl.c b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> > index 035032e..c466999 100644
> > --- a/drivers/i2c/muxes/i2c-demux-pinctrl.c
> > +++ b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> > @@ -244,6 +244,12 @@ static int i2c_demux_pinctrl_probe(struct platform_device *pdev)
> >
> > props[i].name = devm_kstrdup(&pdev->dev, "status", GFP_KERNEL);
> > props[i].value = devm_kstrdup(&pdev->dev, "ok", GFP_KERNEL);
>
> It seemed very dubious to use devm_kstrdup here, since
>
yup - which is where the question in the initial pach came
from I felt that this should better be a devm_kasprint() - I
did not understand why it was kstrdup here in the first
place - technically it is not wrong though as the source is not RO
so it will allocate and copy the original string and thus
effectively it behaves like devm_kasprintf
> 1. if the consumer is not freeing the strings it would be sufficient with just
> props[i].name = "status";
> props[i].value = "ok";
>
> 2. if the consumer is freeing the strings, it is very bad to free them twice
> which is what happens with the devm_ prefix.
Why would it be freed twice ? the pointer returned is a seperately allocated objects ?
that needs to be indepdently freed (this is not the devm_kstrdup_const() case)
>
> So, there is no case, AFAICT, where it is sane to use devm_kstrdup.
I think the only technical difference between devm_kstrdup and devm_kasprintf
is effectively a memcpy vs vsnprintf - so here I think devm_kasprintf would
also be the more suitable call to use.
thx!
hofrat
>
> Therefore I had a look at the code, and to me it seems as if the consumer
> very much frees the strings, which means that we are in case 2, and that
> the above should be ordinary kstrdup calls.
>
> Am I missing something?
>
> Cheers,
> Peter
>
> > + if (!props[i].name || !props[i].value) {
> > + dev_err(&pdev->dev,
> > + "chan %d name, value allocation failed\n", i);
> > + err = -ENOMEM;
> > + goto err_rollback;
> > + }
> > props[i].length = 3;
> >
> > of_changeset_init(&priv->chan[i].chgset);
> >
>
