linux-kernel - [PATCH v2] staging: greybus: audio: Check null pointer

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Date:   Wed, 29 Dec 2021 10:28:50 +0800
From:   Jiasheng Jiang <jiasheng@...as.ac.cn>
To:     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, Jiasheng Jiang <jiasheng@...as.ac.cn>
Subject: [PATCH v2] staging: greybus: audio: Check null pointer

On Tue, Dec 28, 2021 at 10:50:22PM +0800, Alex Elder wrote:
> But the two places you're returning are in the middle of a loop (in 
> gbaudio_tplg_create_widget() and gbaudio_tplg_process_kcontrols()).
> Each is building up a sort of hierarchical data structure, and as
> you can see, the existing code takes care to de-construct the partially
> built structure in the event an error occurs before it completes.
>
> There is a chance that your simple return would "work", but by
> reading the surrounding code you should recognize that the proper
> way to handle the error is to jump to the cleanup at the end.

Yes, I agree with your opinion and this time I use "goto error" instead
of directly return in the two callers.
The new patch is as follow.

As the possible alloc failure of devm_kcalloc(), it could return null
pointer.
Therefore, 'strings' should be checked and return NULL if alloc fails to
prevent the dereference of the NULL pointer.
Also, the caller should also deal with the return value of the
gb_generate_enum_strings() and return -ENOMEM if returns NULL.
Moreover, because the memory allocated with devm_kzalloc() will be
freed automatically when the last reference to the device is dropped,
the 'gbe' in gbaudio_tplg_create_enum_kctl() and
gbaudio_tplg_create_enum_ctl() do not need to free manually.
But the 'control' in gbaudio_tplg_create_widget() and
gbaudio_tplg_process_kcontrols() has a specially error handle to
cleanup.
So it should be better to cleanup 'control' when fails.

Fixes: e65579e335da ("greybus: audio: topology: Enable enumerated control support")
Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
---
Changelog:

v1 -> v2

*Change 1. Add the cleanup process when alloc fails in two callers and
refine the commit message.
---
 drivers/staging/greybus/audio_topology.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/staging/greybus/audio_topology.c b/drivers/staging/greybus/audio_topology.c
index 1fc7727ab7be..6bba735d2e5c 100644
--- a/drivers/staging/greybus/audio_topology.c
+++ b/drivers/staging/greybus/audio_topology.c
@@ -147,6 +147,9 @@ static const char **gb_generate_enum_strings(struct gbaudio_module_info *gb,
 
 	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++) {
@@ -655,6 +658,8 @@ 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,
@@ -862,6 +867,8 @@ 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,
@@ -1034,6 +1041,10 @@ static int gbaudio_tplg_create_widget(struct gbaudio_module_info *module,
 			csize += le16_to_cpu(gbenum->names_length);
 			control->texts = (const char * const *)
 				gb_generate_enum_strings(module, gbenum);
+			if (!control->texts) {
+				ret = -ENOMEM;
+				goto error;
+			}
 			control->items = le32_to_cpu(gbenum->items);
 		} else {
 			csize = sizeof(struct gb_audio_control);
@@ -1183,6 +1194,10 @@ static int gbaudio_tplg_process_kcontrols(struct gbaudio_module_info *module,
 			csize += le16_to_cpu(gbenum->names_length);
 			control->texts = (const char * const *)
 				gb_generate_enum_strings(module, gbenum);
+			if (!control->texts) {
+				ret = -ENOMEM;
+				goto error;
+			}
 			control->items = le32_to_cpu(gbenum->items);
 		} else {
 			csize = sizeof(struct gb_audio_control);
-- 
2.25.1