[PATCH v5 0/2] HID: multitouch: fix use-after-free of haptic data on delayed input release

[PATCH v5 0/2] HID: multitouch: fix use-after-free of haptic data on delayed input release

[Aldo Ariel Panzardo]

Hi Benjamin,

Thanks for the feedback on v4.  Reworked as you asked -- devm_kzalloc
stays, a devm_add_action() handles teardown, and the try_module_get
reorder is now a separate patch.

Patch 1 moves try_module_get()/get_device() before input_ff_create()
so the old input_free error path (which returned ret == 0) goes away.

Patch 2 adds a devm_add_action() callback in hid_haptic_init() that
does all the resource teardown at unbind.  hid_haptic_destroy() just
sets ff->private = NULL so the subsequent kfree in input_ff_destroy
is harmless.  input_get_device() pins the input device for the
duration of the devres action.

Changes since v4:
  - keep devm_kzalloc, use devm_add_action (Benjamin)
  - split reorder into its own patch (Benjamin)
  - single-owner teardown -- destroy only NULLs ff->private,
    devm action owns workqueue drain + buffer frees + ref puts
  - input_get_device pins input_dev against concurrent release
  - workqueue drained before any pointer NULLs or frees
  - input_ff_destroy on devm_add_action failure
  - no hid-multitouch.c or hid-haptic.h changes

v4: https://lore.kernel.org/linux-input/20261009103333.2476105-1-qwe.aldo@gmail.com/
v3: https://lore.kernel.org/linux-input/20261009110509.2432308-1-qwe.aldo@gmail.com/
v1: https://lore.kernel.org/linux-input/20261009031207.3233206-1-qwe.aldo@gmail.com/

Aldo Ariel Panzardo (2):
  HID: haptic: reorder try_module_get/get_device before input_ff_create
  HID: multitouch: fix use-after-free of haptic data on delayed input
    release

 drivers/hid/hid-haptic.c | 87 ++++++++++++++++++++++++++++------------
 1 file changed, 62 insertions(+), 25 deletions(-)

--
2.53.0

[PATCH v5 1/2] HID: haptic: reorder try_module_get/get_device before input_ff_create

[Aldo Ariel Panzardo]

Move try_module_get() and get_device() before input_ff_create() in
hid_haptic_init().  The original order placed them after
input_ff_create(), and failures went to input_free which called
input_ff_destroy() without ever setting ret.  The caller saw ret == 0
on failure and kept a dangling pointer to the haptic struct.

With the references acquired first, all failure paths reach
stop_buffer_free directly.  The flush/event save/restore is no longer
needed.

Fixes: 8d0bf7908b5a ("HID: multitouch: add haptic multitouch support")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 drivers/hid/hid-haptic.c | 33 ++++++++++++++-------------------
 1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
index 8760eeb..592b44e 100644
--- a/drivers/hid/hid-haptic.c
+++ b/drivers/hid/hid-haptic.c
@@ -419,8 +419,6 @@ int hid_haptic_init(struct hid_device *hdev,
 	};
 	const char *prefix = "hid-haptic";
 	char *name;
-	int (*flush)(struct input_dev *dev, struct file *file);
-	int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value);
 
 	haptic->hdev = hdev;
 	haptic->max_waveform_id = max(2u, haptic->max_waveform_id);
@@ -501,11 +499,23 @@ int hid_haptic_init(struct hid_device *hdev,
 
 	input_set_capability(dev, EV_FF, FF_HAPTIC);
 
-	flush = dev->flush;
-	event = dev->event;
+	if (!try_module_get(THIS_MODULE)) {
+		dev_err(&hdev->dev, "Failed to increase module count.\n");
+		ret = -ENODEV;
+		goto stop_buffer_free;
+	}
+	if (!get_device(&hdev->dev)) {
+		dev_err(&hdev->dev, "Failed to get hdev device.\n");
+		ret = -ENODEV;
+		module_put(THIS_MODULE);
+		goto stop_buffer_free;
+	}
+
 	ret = input_ff_create(dev, FF_MAX_EFFECTS);
 	if (ret) {
 		dev_err(&hdev->dev, "Failed to create ff device.\n");
+		put_device(&hdev->dev);
+		module_put(THIS_MODULE);
 		goto stop_buffer_free;
 	}
 
@@ -515,23 +525,8 @@ int hid_haptic_init(struct hid_device *hdev,
 	ff->playback = hid_haptic_playback;
 	ff->erase = hid_haptic_erase;
 	ff->destroy = hid_haptic_destroy;
-	if (!try_module_get(THIS_MODULE)) {
-		dev_err(&hdev->dev, "Failed to increase module count.\n");
-		goto input_free;
-	}
-	if (!get_device(&hdev->dev)) {
-		dev_err(&hdev->dev, "Failed to get hdev device.\n");
-		module_put(THIS_MODULE);
-		goto input_free;
-	}
 	return 0;
 
-input_free:
-	input_ff_destroy(dev);
-	/* Restore dev flush and event */
-	dev->flush = flush;
-	dev->event = event;
-	return ret;
 stop_buffer_free:
 	kfree(haptic->stop_effect.report_buf);
 	haptic->stop_effect.report_buf = NULL;
-- 
2.53.0

[PATCH v5 2/2] HID: multitouch: fix use-after-free of haptic data on delayed input release

[Aldo Ariel Panzardo]

mt_probe() allocates td->haptic with devm_kzalloc() and hid_haptic_init()
stores it in ff->private.  When the HID device is removed while an evdev
fd is still held, devres frees td->haptic at unbind but
hid_haptic_destroy() runs later from input_dev_release() and dereferences
the freed pointer.  input_ff_destroy() then double-frees it via
kfree(ff->private).

Move all resource cleanup into a devm_add_action() callback so it runs
at unbind before devres frees the struct.  hid_haptic_destroy() becomes
just ff->private = NULL, making the later kfree a no-op.  The input
device is pinned with input_get_device() to prevent concurrent release
during the devres action; the workqueue is drained first while all
buffers are still live.

Fixes: 8d0bf7908b5a ("HID: multitouch: add haptic multitouch support")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 drivers/hid/hid-haptic.c | 65 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 57 insertions(+), 8 deletions(-)

diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
index 592b44e..109b4df 100644
--- a/drivers/hid/hid-haptic.c
+++ b/drivers/hid/hid-haptic.c
@@ -379,32 +379,57 @@ static int hid_haptic_erase(struct input_dev *dev, int effect_id)
 
 static void hid_haptic_destroy(struct ff_device *ff)
 {
-	struct hid_haptic_device *haptic = ff->private;
-	struct hid_device *hdev = haptic->hdev;
+	/*
+	 * Resource cleanup is handled by hid_haptic_devm_release() which
+	 * runs at driver unbind.  This callback only disconnects the FF
+	 * subsystem's pointer so input_ff_destroy()'s kfree(ff->private)
+	 * becomes kfree(NULL), preventing a double-free of the
+	 * devres-managed haptic struct.
+	 */
+	ff->private = NULL;
+}
+
+static void hid_haptic_devm_release(void *data)
+{
+	struct hid_haptic_device *haptic = data;
+	struct input_dev *dev = haptic->input_dev;
 	int r;
 
-	if (hdev)
-		put_device(&hdev->dev);
+	/*
+	 * Drain pending work first -- handlers dereference ff->private
+	 * through the input_dev, so the workqueue must be idle before
+	 * we NULL that pointer or free any buffers.
+	 */
+	if (haptic->wq) {
+		destroy_workqueue(haptic->wq);
+		haptic->wq = NULL;
+	}
+
+	if (dev && dev->ff && dev->ff->private == haptic)
+		dev->ff->private = NULL;
+
+	if (haptic->hdev)
+		put_device(&haptic->hdev->dev);
 
 	kfree(haptic->stop_effect.report_buf);
 	haptic->stop_effect.report_buf = NULL;
 
 	if (haptic->effect) {
-		for (r = 0; r < ff->max_effects; r++)
+		for (r = 0; r < FF_MAX_EFFECTS; r++)
 			kfree(haptic->effect[r].report_buf);
 		kfree(haptic->effect);
 	}
 	haptic->effect = NULL;
 
-	destroy_workqueue(haptic->wq);
-	haptic->wq = NULL;
-
 	kfree(haptic->duration_map);
 	haptic->duration_map = NULL;
 
 	kfree(haptic->hid_usage_map);
 	haptic->hid_usage_map = NULL;
 
+	if (dev)
+		input_put_device(dev);
+
 	module_put(THIS_MODULE);
 }
 
@@ -419,6 +444,9 @@ int hid_haptic_init(struct hid_device *hdev,
 	};
 	const char *prefix = "hid-haptic";
 	char *name;
+	int (*flush)(struct input_dev *dev, struct file *file);
+	int (*event)(struct input_dev *dev, unsigned int type,
+		     unsigned int code, int value);
 
 	haptic->hdev = hdev;
 	haptic->max_waveform_id = max(2u, haptic->max_waveform_id);
@@ -511,6 +539,8 @@ int hid_haptic_init(struct hid_device *hdev,
 		goto stop_buffer_free;
 	}
 
+	flush = dev->flush;
+	event = dev->event;
 	ret = input_ff_create(dev, FF_MAX_EFFECTS);
 	if (ret) {
 		dev_err(&hdev->dev, "Failed to create ff device.\n");
@@ -525,6 +555,25 @@ int hid_haptic_init(struct hid_device *hdev,
 	ff->playback = hid_haptic_playback;
 	ff->erase = hid_haptic_erase;
 	ff->destroy = hid_haptic_destroy;
+
+	/*
+	 * Pin the input device so it cannot be released concurrently
+	 * with our devres cleanup.  hid_haptic_devm_release() drops
+	 * this reference after cleanup is complete.
+	 */
+	input_get_device(dev);
+
+	ret = devm_add_action(&hdev->dev, hid_haptic_devm_release, haptic);
+	if (ret) {
+		input_ff_destroy(dev);
+		dev->flush = flush;
+		dev->event = event;
+		input_put_device(dev);
+		put_device(&hdev->dev);
+		module_put(THIS_MODULE);
+		goto stop_buffer_free;
+	}
+
 	return 0;
 
 stop_buffer_free:
-- 
2.53.0

Re: [PATCH v5 1/2] HID: haptic: reorder try_module_get/get_device before input_ff_create

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] input: missing EV_FF capability cleanup on failure leads to NULL deref
--

commit 58557bc733a3a68f242cf09872b1a593ec599fc2
Author: Aldo Ariel Panzardo <qwe.aldo@gmail.com>

HID: haptic: reorder try_module_get/get_device before input_ff_create

This commit moves try_module_get() and get_device() before input_ff_create()
in hid_haptic_init() to acquire references early. It adjusts the error
handling to jump to stop_buffer_free directly on failure, removing the need
to restore handlers or call input_ff_destroy().

> diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
> index 8760eeb08b2cd..592b44e020d6b 100644
> --- a/drivers/hid/hid-haptic.c
> +++ b/drivers/hid/hid-haptic.c

[ ... ]

> @@ -499,11 +499,23 @@ int hid_haptic_init(struct hid_device *hdev,
>  
>  	input_set_capability(dev, EV_FF, FF_HAPTIC);
>  
> -	flush = dev->flush;
> -	event = dev->event;
> +	if (!try_module_get(THIS_MODULE)) {
> +		dev_err(&hdev->dev, "Failed to increase module count.\n");
> +		ret = -ENODEV;
> +		goto stop_buffer_free;
> +	}

[Severity: High]
Does this error path leave the EV_FF capability set on the input device?

Before this change, the failure paths for try_module_get() and get_device()
jumped to input_free, which called input_ff_destroy(dev).

By jumping to stop_buffer_free instead, the EV_FF capability remains set on
the device, but dev->ff is never initialized.

If hid_haptic_init() returns an error that is ignored by its caller, the
partially initialized input device could be registered.

When a userspace application opens the input event node and issues a force
feedback ioctl, could the input core's input_ff_upload() dereference a null
pointer?

For example, in drivers/input/ff-core.c:input_ff_upload():

        if (!test_bit(effect->type, ff->ffbit)) {

Because test_bit(EV_FF, dev->evbit) is true, the input core might assume
dev->ff is valid (where ff aliases dev->ff) and cause a kernel panic.

> +	if (!get_device(&hdev->dev)) {
> +		dev_err(&hdev->dev, "Failed to get hdev device.\n");
> +		ret = -ENODEV;
> +		module_put(THIS_MODULE);
> +		goto stop_buffer_free;
> +	}
> +
>  	ret = input_ff_create(dev, FF_MAX_EFFECTS);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261016135516.2957381-1-qwe.aldo@gmail.com?part=1

Re: [PATCH v5 2/2] HID: multitouch: fix use-after-free of haptic data on delayed input release

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] input: module code UAF due to premature module_put() on unbind
- [High] hid: double-put of hdev and input_dev on multiple haptic touchpad collections
--

commit 058030eab60c1764e5ac8d06b32cafc8846c4171
Author: Aldo Ariel Panzardo <qwe.aldo@gmail.com>

HID: multitouch: fix use-after-free of haptic data on delayed input release

This commit moves haptic resource cleanup into a devm action so it runs at
driver unbind before the haptic struct is freed. It also pins the input
device and delays clearing ff->private to prevent double-frees if the
input device release is delayed.

> diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
> --- a/drivers/hid/hid-haptic.c
> +++ b/drivers/hid/hid-haptic.c
> @@ -379,32 +379,57 @@ static int hid_haptic_erase(struct input_dev *dev, int effect_id)
[ ... ]
> +static void hid_haptic_devm_release(void *data)
> +{
> +	struct hid_haptic_device *haptic = data;
> +	struct input_dev *dev = haptic->input_dev;
>  	int r;
>  
[ ... ]
> +	if (haptic->hdev)
> +		put_device(&haptic->hdev->dev);

[Severity: High]
If a composite HID device presents multiple HID_DG_TOUCHPAD application
collections with haptic usages, mt_input_configured() in hid-multitouch.c
will invoke hid_haptic_input_configured() and hid_haptic_init() multiple
times for the same device.

This causes hid_haptic_init() to queue multiple identical devm release
actions using the same haptic data pointer.

During unbind, this release function will execute multiple times. Because
haptic->hdev is not set to NULL after the first put_device(), will this
result in a double-put of the hdev reference count?

[ ... ]
> +	if (dev)
> +		input_put_device(dev);

[Severity: High]
Similarly, the local dev variable here is populated at the start of the
function from haptic->input_dev. If the release action runs multiple times
for the same haptic struct, will this result in a double-put of the
input_dev reference count as well?

> +
> +	module_put(THIS_MODULE);
>  }

[Severity: High]
The devres action runs synchronously during driver unbind. If an application
holds an open file descriptor to the input device, the input_dev structure
and its ff_device are kept alive after unbind.

Since module_put() executes here, the module's reference count drops, allowing
the system to unload the HID driver module.

When the application eventually closes the file descriptor, the last reference
to the input_dev is dropped. This triggers input_dev_release() which calls
input_ff_destroy().

input_ff_destroy() unconditionally invokes:

    if (ff->destroy)
        ff->destroy(ff);
        
Since dev->ff->destroy was not cleared and still points to hid_haptic_destroy()
inside the unloaded module, does this result in the execution of unmapped
memory?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261016135516.2957381-1-qwe.aldo@gmail.com?part=2

[PATCH v6 0/2] HID: multitouch: fix use-after-free of haptic data on delayed input release

[Aldo Ariel Panzardo]

v6 fixes issues found by Sashiko on v5.

Patch 1 is unchanged -- reorders try_module_get()/get_device() before
input_ff_create().

Patch 2 keeps the devm_add_action() design.  Changes since v5:
  - module_put moved to hid_haptic_destroy so the module stays loaded
    until the FF subsystem is done with the callback; a second
    __module_get covers hid_haptic_devm_release itself
  - guard against double-init (return 0 when haptic->wq is set)
  - NULL haptic->hdev and haptic->input_dev after put in devm_release
  - restore dev->flush/event after input_ff_destroy on devm_add_action
    failure

v5: https://lore.kernel.org/linux-input/20261016135516.2957381-1-qwe.aldo@gmail.com/
v4: https://lore.kernel.org/linux-input/20261009103333.2476105-1-qwe.aldo@gmail.com/
v1: https://lore.kernel.org/linux-input/20261009031207.3233206-1-qwe.aldo@gmail.com/

Aldo Ariel Panzardo (2):
  HID: haptic: reorder try_module_get/get_device before input_ff_create
  HID: multitouch: fix use-after-free of haptic data on delayed input
    release

 drivers/hid/hid-haptic.c | 93 ++++++++++++++++++++++++++++++++++------
 1 file changed, 80 insertions(+), 13 deletions(-)

--
2.53.0

[PATCH v6 1/2] HID: haptic: reorder try_module_get/get_device before input_ff_create

[Aldo Ariel Panzardo]

Move try_module_get() and get_device() before input_ff_create() in
hid_haptic_init().  The original order placed them after
input_ff_create(), and failures went to input_free which called
input_ff_destroy() without ever setting ret.  The caller saw ret == 0
on failure and kept a dangling pointer to the haptic struct.

With the references acquired first, all failure paths reach
stop_buffer_free directly.  The flush/event save/restore is no longer
needed.

Fixes: 8d0bf7908b5a ("HID: multitouch: add haptic multitouch support")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 drivers/hid/hid-haptic.c | 33 ++++++++++++++-------------------
 1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
index 8760eeb..592b44e 100644
--- a/drivers/hid/hid-haptic.c
+++ b/drivers/hid/hid-haptic.c
@@ -419,8 +419,6 @@ int hid_haptic_init(struct hid_device *hdev,
 	};
 	const char *prefix = "hid-haptic";
 	char *name;
-	int (*flush)(struct input_dev *dev, struct file *file);
-	int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value);
 
 	haptic->hdev = hdev;
 	haptic->max_waveform_id = max(2u, haptic->max_waveform_id);
@@ -501,11 +499,23 @@ int hid_haptic_init(struct hid_device *hdev,
 
 	input_set_capability(dev, EV_FF, FF_HAPTIC);
 
-	flush = dev->flush;
-	event = dev->event;
+	if (!try_module_get(THIS_MODULE)) {
+		dev_err(&hdev->dev, "Failed to increase module count.\n");
+		ret = -ENODEV;
+		goto stop_buffer_free;
+	}
+	if (!get_device(&hdev->dev)) {
+		dev_err(&hdev->dev, "Failed to get hdev device.\n");
+		ret = -ENODEV;
+		module_put(THIS_MODULE);
+		goto stop_buffer_free;
+	}
+
 	ret = input_ff_create(dev, FF_MAX_EFFECTS);
 	if (ret) {
 		dev_err(&hdev->dev, "Failed to create ff device.\n");
+		put_device(&hdev->dev);
+		module_put(THIS_MODULE);
 		goto stop_buffer_free;
 	}
 
@@ -515,23 +525,8 @@ int hid_haptic_init(struct hid_device *hdev,
 	ff->playback = hid_haptic_playback;
 	ff->erase = hid_haptic_erase;
 	ff->destroy = hid_haptic_destroy;
-	if (!try_module_get(THIS_MODULE)) {
-		dev_err(&hdev->dev, "Failed to increase module count.\n");
-		goto input_free;
-	}
-	if (!get_device(&hdev->dev)) {
-		dev_err(&hdev->dev, "Failed to get hdev device.\n");
-		module_put(THIS_MODULE);
-		goto input_free;
-	}
 	return 0;
 
-input_free:
-	input_ff_destroy(dev);
-	/* Restore dev flush and event */
-	dev->flush = flush;
-	dev->event = event;
-	return ret;
 stop_buffer_free:
 	kfree(haptic->stop_effect.report_buf);
 	haptic->stop_effect.report_buf = NULL;
-- 
2.53.0

[PATCH v6 2/2] HID: multitouch: fix use-after-free of haptic data on delayed input release

[Aldo Ariel Panzardo]

mt_probe() allocates td->haptic with devm_kzalloc() and hid_haptic_init()
stores it in ff->private.  When the HID device is removed while an evdev
fd is still held, devres frees td->haptic at unbind but
hid_haptic_destroy() runs later from input_dev_release() and dereferences
the freed pointer.  input_ff_destroy() then double-frees it via
kfree(ff->private).

Move all resource cleanup into a devm_add_action() callback so it runs
at unbind before devres frees the struct.  hid_haptic_destroy() becomes
ff->private = NULL plus module_put() -- keeping the module loaded until
the FF subsystem is done with the callback.  The input device is pinned
with input_get_device() to prevent concurrent release during the devres
action; the workqueue is drained first while all buffers are still live.

Guard against double-init when multiple touchpad collections trigger
hid_haptic_init() for the same haptic struct.

Fixes: 8d0bf7908b5a ("HID: multitouch: add haptic multitouch support")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 drivers/hid/hid-haptic.c | 74 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 66 insertions(+), 8 deletions(-)

diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
index 592b44e..6d72d9c 100644
--- a/drivers/hid/hid-haptic.c
+++ b/drivers/hid/hid-haptic.c
@@ -379,32 +379,61 @@ static int hid_haptic_erase(struct input_dev *dev, int effect_id)
 
 static void hid_haptic_destroy(struct ff_device *ff)
 {
-	struct hid_haptic_device *haptic = ff->private;
-	struct hid_device *hdev = haptic->hdev;
+	/*
+	 * Resource cleanup is handled by hid_haptic_devm_release() at
+	 * driver unbind.  Disconnect the FF pointer so input_ff_destroy()'s
+	 * kfree(ff->private) becomes kfree(NULL).  Drop the module
+	 * reference last -- it must outlive this callback.
+	 */
+	ff->private = NULL;
+	module_put(THIS_MODULE);
+}
+
+static void hid_haptic_devm_release(void *data)
+{
+	struct hid_haptic_device *haptic = data;
+	struct input_dev *dev = haptic->input_dev;
 	int r;
 
-	if (hdev)
-		put_device(&hdev->dev);
+	/*
+	 * Drain pending work first -- handlers dereference ff->private
+	 * through the input_dev, so the workqueue must be idle before
+	 * we NULL that pointer or free any buffers.
+	 */
+	if (haptic->wq) {
+		destroy_workqueue(haptic->wq);
+		haptic->wq = NULL;
+	}
+
+	if (dev && dev->ff && dev->ff->private == haptic)
+		dev->ff->private = NULL;
+
+	if (haptic->hdev) {
+		put_device(&haptic->hdev->dev);
+		haptic->hdev = NULL;
+	}
 
 	kfree(haptic->stop_effect.report_buf);
 	haptic->stop_effect.report_buf = NULL;
 
 	if (haptic->effect) {
-		for (r = 0; r < ff->max_effects; r++)
+		for (r = 0; r < FF_MAX_EFFECTS; r++)
 			kfree(haptic->effect[r].report_buf);
 		kfree(haptic->effect);
 	}
 	haptic->effect = NULL;
 
-	destroy_workqueue(haptic->wq);
-	haptic->wq = NULL;
-
 	kfree(haptic->duration_map);
 	haptic->duration_map = NULL;
 
 	kfree(haptic->hid_usage_map);
 	haptic->hid_usage_map = NULL;
 
+	if (dev) {
+		input_put_device(dev);
+		haptic->input_dev = NULL;
+	}
+
 	module_put(THIS_MODULE);
 }
 
@@ -414,12 +443,17 @@ int hid_haptic_init(struct hid_device *hdev,
 {
 	struct ff_device *ff;
 	int ret = 0, r;
+	int (*saved_flush)(struct input_dev *, struct file *);
+	int (*saved_event)(struct input_dev *, unsigned int, unsigned int, int);
 	struct ff_haptic_effect stop_effect = {
 		.hid_usage = HID_HP_WAVEFORMSTOP & HID_USAGE,
 	};
 	const char *prefix = "hid-haptic";
 	char *name;
 
+	if (haptic->wq)
+		return 0;
+
 	haptic->hdev = hdev;
 	haptic->max_waveform_id = max(2u, haptic->max_waveform_id);
 	haptic->max_duration_id = max(2u, haptic->max_duration_id);
@@ -511,6 +545,8 @@ int hid_haptic_init(struct hid_device *hdev,
 		goto stop_buffer_free;
 	}
 
+	saved_flush = dev->flush;
+	saved_event = dev->event;
 	ret = input_ff_create(dev, FF_MAX_EFFECTS);
 	if (ret) {
 		dev_err(&hdev->dev, "Failed to create ff device.\n");
@@ -525,6 +561,28 @@ int hid_haptic_init(struct hid_device *hdev,
 	ff->playback = hid_haptic_playback;
 	ff->erase = hid_haptic_erase;
 	ff->destroy = hid_haptic_destroy;
+
+	/*
+	 * Pin the input device so it cannot be released concurrently
+	 * with our devres cleanup, and take a second module reference
+	 * so the module stays loaded while hid_haptic_devm_release()
+	 * executes (the first ref is dropped by hid_haptic_destroy()
+	 * which may run inside input_put_device() below).
+	 */
+	input_get_device(dev);
+	__module_get(THIS_MODULE);
+
+	ret = devm_add_action(&hdev->dev, hid_haptic_devm_release, haptic);
+	if (ret) {
+		module_put(THIS_MODULE);
+		input_ff_destroy(dev);
+		dev->flush = saved_flush;
+		dev->event = saved_event;
+		input_put_device(dev);
+		put_device(&hdev->dev);
+		goto stop_buffer_free;
+	}
+
 	return 0;
 
 stop_buffer_free:
-- 
2.53.0

Re: [PATCH v6 1/2] HID: haptic: reorder try_module_get/get_device before input_ff_create

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] input: NULL pointer dereference in evdev on EVIOCGEFFECTS when hid_haptic_init fails
--

commit 2755afe0061688f07b774dbe02464fb532ab3852
Author: Aldo Ariel Panzardo <qwe.aldo@gmail.com>

HID: haptic: reorder try_module_get/get_device before input_ff_create

This commit moves try_module_get() and get_device() calls before
input_ff_create() to fix a dangling pointer and uninitialized return value
in the error path of hid_haptic_init().

> diff --git a/drivers/hid/hid-haptic.c b/drivers/hid/hid-haptic.c
> index 8760eeb08b2cd..592b44e020d6b 100644
> --- a/drivers/hid/hid-haptic.c
> +++ b/drivers/hid/hid-haptic.c
> @@ -501,11 +499,23 @@ int hid_haptic_init(struct hid_device *hdev,
>  
>  	input_set_capability(dev, EV_FF, FF_HAPTIC);
>  
> -	flush = dev->flush;
> -	event = dev->event;
> +	if (!try_module_get(THIS_MODULE)) {
> +		dev_err(&hdev->dev, "Failed to increase module count.\n");
> +		ret = -ENODEV;
> +		goto stop_buffer_free;
> +	}
> +	if (!get_device(&hdev->dev)) {
> +		dev_err(&hdev->dev, "Failed to get hdev device.\n");
> +		ret = -ENODEV;
> +		module_put(THIS_MODULE);
> +		goto stop_buffer_free;
> +	}
> +
>  	ret = input_ff_create(dev, FF_MAX_EFFECTS);
>  	if (ret) {
>  		dev_err(&hdev->dev, "Failed to create ff device.\n");
> +		put_device(&hdev->dev);
> +		module_put(THIS_MODULE);
>  		goto stop_buffer_free;
>  	}

[Severity: High]
Can this cause a NULL pointer dereference in evdev if try_module_get() or
get_device() fails?

By setting EV_FF on the device unconditionally via input_set_capability()
before these checks, if we hit the stop_buffer_free error path, EV_FF
remains set but dev->ff is never initialized.

Because the caller hid_haptic_input_configured() masks the error:

drivers/hid/hid-haptic.c:hid_haptic_input_configured() {
    ...
	error = hid_haptic_init(hdev, haptic, hi->input);
	if (error) {
		dev_warn(&hdev->dev, "Cannot allocate haptic for %s\n",
			 hdev->name);
		return 0;
	}
    ...
}

The input device will still be successfully registered with the EV_FF
capability. When userspace subsequently issues an EVIOCGEFFECTS ioctl,
evdev_do_ioctl() checks EV_FF and blindly dereferences dev->ff:

drivers/input/evdev.c:evdev_do_ioctl() {
    ...
	case EVIOCGEFFECTS:
		i = test_bit(EV_FF, dev->evbit) ?
				dev->ff->max_effects : 0;
    ...
}

Since dev->ff is NULL, this will cause a kernel panic. Should the EV_FF
capability be cleared in the stop_buffer_free error path, or only set
after these checks succeed?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261016151343.3120300-1-qwe.aldo@gmail.com?part=1