linux-kernel - Re: [PATCH] media: meson: Add NULL check after the call to kmalloc()

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Message-ID: <CADLLry6WYJRWz1mkgO-fvKeRmOhOJQ3S_hXH1sBW11TujT-a1g@mail.gmail.com>
Date:   Thu, 5 Sep 2019 07:47:39 +0900
From:   Austin Kim <austindh.kim@...il.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     mchehab@...nel.org, khilman@...libre.com, mjourdan@...libre.com,
        gregkh@...uxfoundation.org, linux-media@...r.kernel.org,
        linux-amlogic@...ts.infradead.org, devel@...verdev.osuosl.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: meson: Add NULL check after the call to kmalloc()

2019년 9월 4일 (수) 오후 5:43, Rasmus Villemoes <linux@...musvillemoes.dk>님이 작성:
>
> On 04/09/2019 10.22, Austin Kim wrote:
> > If the kmalloc() return NULL, the NULL pointer dereference will occur.
> >       new_ts->ts = ts;
> >
> > Add exception check after the call to kmalloc() is made.
> >
> > Signed-off-by: Austin Kim <austindh.kim@...il.com>
> > ---
> >  drivers/staging/media/meson/vdec/vdec_helpers.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/staging/media/meson/vdec/vdec_helpers.c b/drivers/staging/media/meson/vdec/vdec_helpers.c
> > index f16948b..e7e56d5 100644
> > --- a/drivers/staging/media/meson/vdec/vdec_helpers.c
> > +++ b/drivers/staging/media/meson/vdec/vdec_helpers.c
> > @@ -206,6 +206,10 @@ void amvdec_add_ts_reorder(struct amvdec_session *sess, u64 ts, u32 offset)
> >       unsigned long flags;
> >
> >       new_ts = kmalloc(sizeof(*new_ts), GFP_KERNEL);
> > +     if (!new_ts) {
> > +             dev_err(sess->core->dev, "Failed to kmalloc()\n");
> > +             return;
> > +     }
> >       new_ts->ts = ts;
> >       new_ts->offset = offset;
>
> No need to printk() on error, AFAIK the mm subsystem should already make
> some noise if an allocation fails.

Thanks for valuable feedback.
BTW, if the kmalloc return NULL, mm subsystem throws error log with 100%?
If no, please share error signature of kernel.

> This is not a proper fix - you need to make the function return an error
> (-ENOMEM) to let the caller know allocation failed, and allow that to
> propagate the error. There's only one caller, which already seems
> capable of returning errors (there's an -EAGAIN), so it shouldn't be
> that hard - though of course one needs to undo what has been done so far.
>
> Also, unrelated to the kmalloc() handling: amvdec_add_ts_reorder() could
> be moved to esparser.c and made static, or at the very least the
> EXPORT_SYMBOL can be removed since vdec_helpers.o is linked in to the
> same module as the sole user. That probably goes for all the
> EXPORT_SYMBOL(amvdec_*).

I agreed with your feedback.
- On memory allocation failure, it should have returned (-ENOMEM)
rather than 'return' statement.
- The call to amvdec_add_ts_reorder() is only made by esparser_queue().

Let me resend the patch if necessary.

Thanks,
Austin Kim
>
> Rasmus