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

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Date:   Wed, 4 Sep 2019 10:43:20 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Austin Kim <austindh.kim@...il.com>, mchehab@...nel.org,
        khilman@...libre.com
Cc:     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()

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.
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_*).

Rasmus