linux-kernel - Re: [PATCH] staging: greybus: audio: Check null pointer

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Message-ID: <91f92fda-e8cf-c96d-26b2-56a860ac7cf1@ieee.org>
Date:   Mon, 27 Dec 2021 09:54:10 -0600
From:   Alex Elder <elder@...e.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>, vaibhav.sr@...il.com,
        mgreer@...malcreek.com, johan@...nel.org, elder@...nel.org,
        gregkh@...uxfoundation.org
Cc:     greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: greybus: audio: Check null pointer

On 12/24/21 3:03 AM, Jiasheng Jiang wrote:
> As the possible alloc failure of devm_kcalloc, it could return null
> pointer.
> To prevent the dereference of the null pointer, it should be checked.

I think this is a good change, but I would like you to improve
the description, and fix some different bugs introduced by your
change.

What you are specifically doing is checking for a null return
from devm_kcalloc() in gb_generate_enum_strings(), and are
returning the NULL pointer if that occurs.  That means you
need to update all the callers of gb_generate_enum_strings()
to also handle a possible null return value.

The fix does a good thing, and your description is correct
about what you are fixing.  But it should supply more
complete context for the change.

More below.

> Fixes: e65579e335da ("greybus: audio: topology: Enable enumerated control support")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>   drivers/staging/greybus/audio_topology.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/staging/greybus/audio_topology.c b/drivers/staging/greybus/audio_topology.c
> index 1fc7727ab7be..e9f47a1f0d28 100644
> --- a/drivers/staging/greybus/audio_topology.c
> +++ b/drivers/staging/greybus/audio_topology.c
> @@ -146,7 +146,11 @@ static const char **gb_generate_enum_strings(struct gbaudio_module_info *gb,
>   	__u8 *data;
>   
>   	items = le32_to_cpu(gbenum->items);
> +
>   	strings = devm_kcalloc(gb->dev, items, sizeof(char *), GFP_KERNEL);
> +	if (!strings)
> +		return NULL;
> +
>   	data = gbenum->names;
>   
>   	for (i = 0; i < items; i++) {
> @@ -654,7 +658,10 @@ static int gbaudio_tplg_create_enum_kctl(struct gbaudio_module_info *gb,
>   
>   	/* since count=1, and reg is dummy */
>   	gbe->items = le32_to_cpu(gb_enum->items);
> +
>   	gbe->texts = gb_generate_enum_strings(gb, gb_enum);
> +	if (!gbe->texts)
> +		return -ENOMEM;
>   
>   	/* debug enum info */
>   	dev_dbg(gb->dev, "Max:%d, name_length:%d\n", gbe->items,
> @@ -861,7 +868,10 @@ static int gbaudio_tplg_create_enum_ctl(struct gbaudio_module_info *gb,
>   
>   	/* since count=1, and reg is dummy */
>   	gbe->items = le32_to_cpu(gb_enum->items);
> +
>   	gbe->texts = gb_generate_enum_strings(gb, gb_enum);
> +	if (!gbe->texts)
> +		return -ENOMEM;
>   
>   	/* debug enum info */
>   	dev_dbg(gb->dev, "Max:%d, name_length:%d\n", gbe->items,
> @@ -1032,8 +1042,12 @@ static int gbaudio_tplg_create_widget(struct gbaudio_module_info *module,
>   			csize += offsetof(struct gb_audio_ctl_elem_info, value);
>   			csize += offsetof(struct gb_audio_enumerated, names);
>   			csize += le16_to_cpu(gbenum->names_length);
> +
>   			control->texts = (const char * const *)
>   				gb_generate_enum_strings(module, gbenum);
> +			if (!control->texts)
> +				return -ENOMEM;
> +

You can't simply return here.  If you look a bit above this,
where the call to allocate a control structure is done, you
see that a NULL return there jumps to the "error" label, so
any already allocated and initialized control widgets get
cleaned up before returning.

>   			control->items = le32_to_cpu(gbenum->items);
>   		} else {
>   			csize = sizeof(struct gb_audio_control);
> @@ -1181,8 +1195,12 @@ static int gbaudio_tplg_process_kcontrols(struct gbaudio_module_info *module,
>   			csize += offsetof(struct gb_audio_ctl_elem_info, value);
>   			csize += offsetof(struct gb_audio_enumerated, names);
>   			csize += le16_to_cpu(gbenum->names_length);
> +
>   			control->texts = (const char * const *)
>   				gb_generate_enum_strings(module, gbenum);
> +			if (!control->texts)
> +				return -ENOMEM;
> +

You have basically the same issue here.  You can't just return,
you must do some cleanup too.

					-Alex

>   			control->items = le32_to_cpu(gbenum->items);
>   		} else {
>   			csize = sizeof(struct gb_audio_control);
>