[PATCH v4 2/2] ALSA: control: add ioctl to retrieve full card components

[Maciej Strozek <mstrozek@opensource.cirrus.com>]

The fixed-size components field in SNDRV_CTL_IOCTL_CARD_INFO can be too
small on systems with many audio devices.

Keep the existing struct snd_ctl_card_info ABI intact and add a new
ioctl SNDRV_CTL_IOCTL_CARD_BYTES that carries a variable-length payload
selected by a type discriminator. The first defined type
SND_CTL_CARD_BTYPE_COMPONENTS returns the full components string. The
ioctl is designed to be reused for other variable-length card payloads
in the future.

The user-space caller may set data_allocated == 0 (or data == NULL) to
query the required length; otherwise the kernel copies the payload into
the user buffer and writes back the actual length in data_len.

When the legacy components field in struct snd_ctl_card_info is
truncated, '>' is written just before the NUL terminator to signal to
user-space that the full string is available via the new ioctl.

card->components is now dynamically allocated and grown in 32 byte
increments via krealloc(), capped at 512 bytes.

Link: https://github.com/alsa-project/alsa-lib/pull/494
Suggested-by: Jaroslav Kysela <perex@perex.cz>
Suggested-by: Takashi Iwai <tiwai@suse.com>
Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
---
Changes for v4:
 - replaced snd_ctl_card_components with snd_ctl_card_bytes for possible
   future extensions
 - support query mode (data_allocated == 0 or data == NULL)
 - added compat 32-bit
 - renamed card->components_ptr / components_ptr_alloc_size to
   card->components / components_alloc_size
Changes for v3:
 - change components field to a dynamic array resizable in 32 byte
   increments
 - removed SNDRV_CTL_COMPONENTS_LEN define
 - sanity check if 'components' requests more than 512 bytes
 - added a commit to clean up trailing whitespaces
 - alsa-utils link no longer needed
Changes for v2:
 - do not modify existing card->components field
 - add a new ioctl and struct to keep the full components string
 - handle the split/trim in snd_ctl_card_info()
---
 include/sound/core.h        |  4 +--
 include/uapi/sound/asound.h | 21 ++++++++++++++-
 sound/core/control.c        | 52 ++++++++++++++++++++++++++++++++++++-
 sound/core/control_compat.c | 27 +++++++++++++++++++
 sound/core/init.c           | 34 ++++++++++++++++++++----
 5 files changed, 129 insertions(+), 9 deletions(-)

diff --git a/include/sound/core.h b/include/sound/core.h
index 4093ec82a0a12..8a6a0e86da5e5 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -87,8 +87,8 @@ struct snd_card {
 	char longname[80];		/* name of this soundcard */
 	char irq_descr[32];		/* Interrupt description */
 	char mixername[80];		/* mixer name */
-	char components[128];		/* card components delimited with
-								space */
+	char *components;		/* card components, space-delimited */
+	unsigned int components_alloc_size;	/* current allocation size of components */
 	struct module *module;		/* top-level module */

 	void *private_data;		/* private data for soundcard */
diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index d3ce75ba938a8..a6b695a798f07 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -1058,7 +1058,7 @@ struct snd_timer_tread {
  *                                                                          *
  ****************************************************************************/

-#define SNDRV_CTL_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 9)
+#define SNDRV_CTL_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 10)

 struct snd_ctl_card_info {
 	int card;			/* card number */
@@ -1072,6 +1072,24 @@ struct snd_ctl_card_info {
 	unsigned char components[128];	/* card components / fine identification, delimited with one space (AC97 etc..) */
 };

+/*
+ * Card components can exceed the fixed 128 bytes in snd_ctl_card_info.
+ * Use SNDRV_CTL_IOCTL_CARD_BYTES with type SND_CTL_CARD_BTYPE_COMPONENTS
+ * to retrieve the full string.
+ */
+
+/* Type values for struct snd_ctl_card_bytes::type */
+enum {
+	SND_CTL_CARD_BTYPE_COMPONENTS	= 1,	/* full card components string */
+};
+
+struct snd_ctl_card_bytes {
+	unsigned int type;		/* SND_CTL_CARD_BTYPE_* */
+	unsigned int data_allocated;	/* size of @data buffer in bytes */
+	unsigned int data_len;		/* in/out: actual data length in bytes */
+	unsigned char *data;		/* user buffer */
+};
+
 typedef int __bitwise snd_ctl_elem_type_t;
 #define	SNDRV_CTL_ELEM_TYPE_NONE	((__force snd_ctl_elem_type_t) 0) /* invalid */
 #define	SNDRV_CTL_ELEM_TYPE_BOOLEAN	((__force snd_ctl_elem_type_t) 1) /* boolean type */
@@ -1198,6 +1216,7 @@ struct snd_ctl_tlv {

 #define SNDRV_CTL_IOCTL_PVERSION	_IOR('U', 0x00, int)
 #define SNDRV_CTL_IOCTL_CARD_INFO	_IOR('U', 0x01, struct snd_ctl_card_info)
+#define SNDRV_CTL_IOCTL_CARD_BYTES	_IOWR('U', 0x02, struct snd_ctl_card_bytes)
 #define SNDRV_CTL_IOCTL_ELEM_LIST	_IOWR('U', 0x10, struct snd_ctl_elem_list)
 #define SNDRV_CTL_IOCTL_ELEM_INFO	_IOWR('U', 0x11, struct snd_ctl_elem_info)
 #define SNDRV_CTL_IOCTL_ELEM_READ	_IOWR('U', 0x12, struct snd_ctl_elem_value)
diff --git a/sound/core/control.c b/sound/core/control.c
index 5e51857635e62..9a3772f1126d8 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -876,9 +876,13 @@ static int snd_ctl_card_info(struct snd_card *card, struct snd_ctl_file * ctl,
 {
 	struct snd_ctl_card_info *info __free(kfree) =
 		kzalloc(sizeof(*info), GFP_KERNEL);
+	ssize_t n;

 	if (! info)
 		return -ENOMEM;
+
+	static_assert(sizeof(info->components) >= 2);
+
 	scoped_guard(rwsem_read, &snd_ioctl_rwsem) {
 		info->card = card->number;
 		strscpy(info->id, card->id, sizeof(info->id));
@@ -886,13 +890,57 @@ static int snd_ctl_card_info(struct snd_card *card, struct snd_ctl_file * ctl,
 		strscpy(info->name, card->shortname, sizeof(info->name));
 		strscpy(info->longname, card->longname, sizeof(info->longname));
 		strscpy(info->mixername, card->mixername, sizeof(info->mixername));
-		strscpy(info->components, card->components, sizeof(info->components));
+		n = strscpy(info->components, card->components, sizeof(info->components));
+		if (n < 0) // mark the truncation with '>' before NULL terminator
+			info->components[sizeof(info->components) - 2] = '>';
 	}
 	if (copy_to_user(arg, info, sizeof(struct snd_ctl_card_info)))
 		return -EFAULT;
 	return 0;
 }

+static int snd_ctl_card_bytes(struct snd_card *card,
+			      struct snd_ctl_card_bytes *info,
+			      unsigned int __user *data_len_out)
+{
+	unsigned int data_len;
+
+	switch (info->type) {
+	case SND_CTL_CARD_BTYPE_COMPONENTS:
+		scoped_guard(rwsem_read, &snd_ioctl_rwsem) {
+			data_len = strlen(card->components) + 1;
+
+			if (!info->data || info->data_allocated == 0)
+				break;
+
+			if (info->data_allocated < data_len)
+				return -ENOMEM;
+
+			if (copy_to_user(info->data, card->components, data_len))
+				return -EFAULT;
+		}
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (put_user(data_len, data_len_out))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int snd_ctl_card_bytes_user(struct snd_card *card,
+				   struct snd_ctl_card_bytes __user *_info)
+{
+	struct snd_ctl_card_bytes info;
+
+	if (copy_from_user(&info, _info, sizeof(info)))
+		return -EFAULT;
+
+	return snd_ctl_card_bytes(card, &info, &_info->data_len);
+}
+
 static int snd_ctl_elem_list(struct snd_card *card,
 			     struct snd_ctl_elem_list *list)
 {
@@ -1992,6 +2040,8 @@ static long snd_ctl_ioctl(struct file *file, unsigned int cmd, unsigned long arg
 		return put_user(SNDRV_CTL_VERSION, ip) ? -EFAULT : 0;
 	case SNDRV_CTL_IOCTL_CARD_INFO:
 		return snd_ctl_card_info(card, ctl, cmd, argp);
+	case SNDRV_CTL_IOCTL_CARD_BYTES:
+		return snd_ctl_card_bytes_user(card, argp);
 	case SNDRV_CTL_IOCTL_ELEM_LIST:
 		return snd_ctl_elem_list_user(card, argp);
 	case SNDRV_CTL_IOCTL_ELEM_INFO:
diff --git a/sound/core/control_compat.c b/sound/core/control_compat.c
index 4ad571087ff59..9077482d67440 100644
--- a/sound/core/control_compat.c
+++ b/sound/core/control_compat.c
@@ -19,6 +19,30 @@ struct snd_ctl_elem_list32 {
 	unsigned char reserved[50];
 } /* don't set packed attribute here */;

+struct snd_ctl_card_bytes32 {
+	u32 type;
+	u32 data_allocated;
+	u32 data_len;
+	u32 data;
+};
+
+static int snd_ctl_card_bytes_compat(struct snd_card *card,
+				     struct snd_ctl_card_bytes32 __user *data32)
+{
+	struct snd_ctl_card_bytes data = {};
+	compat_caddr_t ptr;
+
+	/* type, data_allocated, data_len */
+	if (copy_from_user(&data, data32, 3 * sizeof(u32)))
+		return -EFAULT;
+	/* data */
+	if (get_user(ptr, &data32->data))
+		return -EFAULT;
+	data.data = compat_ptr(ptr);
+
+	return snd_ctl_card_bytes(card, &data, &data32->data_len);
+}
+
 static int snd_ctl_elem_list_compat(struct snd_card *card,
 				    struct snd_ctl_elem_list32 __user *data32)
 {
@@ -426,6 +450,7 @@ enum {
 	SNDRV_CTL_IOCTL_ELEM_WRITE32 = _IOWR('U', 0x13, struct snd_ctl_elem_value32),
 	SNDRV_CTL_IOCTL_ELEM_ADD32 = _IOWR('U', 0x17, struct snd_ctl_elem_info32),
 	SNDRV_CTL_IOCTL_ELEM_REPLACE32 = _IOWR('U', 0x18, struct snd_ctl_elem_info32),
+	SNDRV_CTL_IOCTL_CARD_BYTES32 = _IOWR('U', 0x02, struct snd_ctl_card_bytes32),
 #ifdef CONFIG_X86_X32_ABI
 	SNDRV_CTL_IOCTL_ELEM_READ_X32 = _IOWR('U', 0x12, struct snd_ctl_elem_value_x32),
 	SNDRV_CTL_IOCTL_ELEM_WRITE_X32 = _IOWR('U', 0x13, struct snd_ctl_elem_value_x32),
@@ -456,6 +481,8 @@ static inline long snd_ctl_ioctl_compat(struct file *file, unsigned int cmd, uns
 	case SNDRV_CTL_IOCTL_TLV_WRITE:
 	case SNDRV_CTL_IOCTL_TLV_COMMAND:
 		return snd_ctl_ioctl(file, cmd, (unsigned long)argp);
+	case SNDRV_CTL_IOCTL_CARD_BYTES32:
+		return snd_ctl_card_bytes_compat(ctl->card, argp);
 	case SNDRV_CTL_IOCTL_ELEM_LIST32:
 		return snd_ctl_elem_list_compat(ctl->card, argp);
 	case SNDRV_CTL_IOCTL_ELEM_INFO32:
diff --git a/sound/core/init.c b/sound/core/init.c
index 593c05895e118..a683803bcf96a 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -590,6 +590,9 @@ static int snd_card_do_free(struct snd_card *card)
 		snd_mixer_oss_notify_callback(card, SND_MIXER_OSS_NOTIFY_FREE);
 #endif
 	snd_device_free_all(card);
+	kfree(card->components);
+	card->components = NULL;
+	card->components_alloc_size = 0;
 	if (card->private_free)
 		card->private_free(card);
 #ifdef CONFIG_SND_CTL_DEBUG
@@ -1036,16 +1039,37 @@ int snd_component_add(struct snd_card *card, const char *component)
 {
 	char *ptr;
 	int len = strlen(component);
+	unsigned int cur_len, need_len;

-	ptr = strstr(card->components, component);
-	if (ptr != NULL) {
-		if (ptr[len] == '\0' || ptr[len] == ' ')	/* already there */
-			return 1;
+	if (card->components) {
+		ptr = strstr(card->components, component);
+		if (ptr) {
+			if (ptr[len] == '\0' || ptr[len] == ' ')	/* already there */
+				return 1;
+		}
+		cur_len = strlen(card->components) + 1;
+	} else {
+		cur_len = 0;
 	}
-	if (strlen(card->components) + 1 + len + 1 > sizeof(card->components)) {
+
+	need_len = cur_len + len + 1;
+	if (need_len > 512) {
 		snd_BUG();
 		return -ENOMEM;
 	}
+
+	if (need_len > card->components_alloc_size) {
+		unsigned int new_alloc = roundup(need_len, 32);
+
+		ptr = krealloc(card->components, new_alloc, GFP_KERNEL);
+		if (!ptr)
+			return -ENOMEM;
+		if (!card->components)
+			ptr[0] = '\0';
+		card->components = ptr;
+		card->components_alloc_size = new_alloc;
+	}
+
 	if (card->components[0] != '\0')
 		strcat(card->components, " ");
 	strcat(card->components, component);
--
2.47.3