[PATCH v2] ALSA: seq: Use flexible array for device arguments

[Cássio Gabriel]

snd_seq_device_new() allocates struct snd_seq_device together with a
caller-specific argument area. SNDRV_SEQ_DEVICE_ARGPTR() reaches that
area by adding sizeof(struct snd_seq_device) to the object pointer.

Make the trailing storage explicit with a flexible array and allocate it
with kzalloc_flex(). This makes the object layout self-describing and
avoids open-coded size arithmetic in the allocation and accessor.

Reject negative argsize values before calculating the allocation size.
Current in-tree callers pass either zero or sizeof() values, but the
function takes an int size argument and should not let a negative value
flow into unsigned allocation arithmetic.

Signed-off-by: Cássio Gabriel <cassiogabrielcontato@xxxxxxxxx>
---
 include/sound/seq_device.h | 3 ++-
 sound/core/seq_device.c    | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/sound/seq_device.h b/include/sound/seq_device.h
index a72380c202e9..3137d4c5f5a8 100644
--- a/include/sound/seq_device.h
+++ b/include/sound/seq_device.h
@@ -22,6 +22,7 @@ struct snd_seq_device {
 	void *private_data;	/* private data for the caller */
 	void (*private_free)(struct snd_seq_device *device);
 	struct device dev;
+	unsigned char args[];	/* driver-specific argument */
 };
 
 #define to_seq_dev(_dev) \
@@ -64,7 +65,7 @@ void snd_seq_device_load_drivers(void);
 int snd_seq_device_new(struct snd_card *card, int device, const char *id,
 		       int argsize, struct snd_seq_device **result);
 
-#define SNDRV_SEQ_DEVICE_ARGPTR(dev) (void *)((char *)(dev) + sizeof(struct snd_seq_device))
+#define SNDRV_SEQ_DEVICE_ARGPTR(dev) ((void *)(dev)->args)
 
 int __must_check __snd_seq_driver_register(struct snd_seq_driver *drv,
 					   struct module *mod);
diff --git a/sound/core/seq_device.c b/sound/core/seq_device.c
index 1b062d6b17ea..8be1f3ab5b63 100644
--- a/sound/core/seq_device.c
+++ b/sound/core/seq_device.c
@@ -234,7 +234,10 @@ int snd_seq_device_new(struct snd_card *card, int device, const char *id,
 	if (snd_BUG_ON(!id))
 		return -EINVAL;
 
-	dev = kzalloc(sizeof(*dev) + argsize, GFP_KERNEL);
+	if (argsize < 0)
+		return -EINVAL;
+
+	dev = kzalloc_flex(*dev, args, argsize);
 	if (!dev)
 		return -ENOMEM;
 

---
base-commit: 5fa82dd6492e9ac3ab27d2c15d73b601b4e6a87d
change-id: 20260531-alsa-seq-flex-args-5b3cf84ef8c0

Best regards,
--  
Cássio Gabriel <cassiogabrielcontato@xxxxxxxxx>