ALSA: compat_ioctl: avoid compat_alloc_user_space

Using compat_alloc_user_space() tends to add complexity
to the ioctl handling, so I am trying to remove it everywhere.

The two callers in sound/core can rewritten to just call
the same code that operates on a kernel pointer as the
native handler.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200918095642.1446243-1-arnd@arndb.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/control.c

@@ -717,22 +717,19 @@ static int snd_ctl_card_info(struct snd_card *card, struct snd_ctl_file * ctl,
 }
 
 static int snd_ctl_elem_list(struct snd_card *card,
-			     struct snd_ctl_elem_list __user *_list)
+			     struct snd_ctl_elem_list *list)
 {
-	struct snd_ctl_elem_list list;
 	struct snd_kcontrol *kctl;
 	struct snd_ctl_elem_id id;
 	unsigned int offset, space, jidx;
 	int err = 0;
 
-	if (copy_from_user(&list, _list, sizeof(list)))
-		return -EFAULT;
-	offset = list.offset;
-	space = list.space;
+	offset = list->offset;
+	space = list->space;
 
 	down_read(&card->controls_rwsem);
-	list.count = card->controls_count;
-	list.used = 0;
+	list->count = card->controls_count;
+	list->used = 0;
 	if (space > 0) {
 		list_for_each_entry(kctl, &card->controls, list) {
 			if (offset >= kctl->count) {
@@ -741,12 +738,12 @@ static int snd_ctl_elem_list(struct snd_card *card,
 			}
 			for (jidx = offset; jidx < kctl->count; jidx++) {
 				snd_ctl_build_ioff(&id, kctl, jidx);
-				if (copy_to_user(list.pids + list.used, &id,
+				if (copy_to_user(list->pids + list->used, &id,
 						 sizeof(id))) {
 					err = -EFAULT;
 					goto out;
 				}
-				list.used++;
+				list->used++;
 				if (!--space)
 					goto out;
 			}
@@ -755,11 +752,26 @@ static int snd_ctl_elem_list(struct snd_card *card,
 	}
  out:
 	up_read(&card->controls_rwsem);
-	if (!err && copy_to_user(_list, &list, sizeof(list)))
-		err = -EFAULT;
 	return err;
 }
 
+static int snd_ctl_elem_list_user(struct snd_card *card,
+				  struct snd_ctl_elem_list __user *_list)
+{
+	struct snd_ctl_elem_list list;
+	int err;
+
+	if (copy_from_user(&list, _list, sizeof(list)))
+		return -EFAULT;
+	err = snd_ctl_elem_list(card, &list);
+	if (err)
+		return err;
+	if (copy_to_user(_list, &list, sizeof(list)))
+		return -EFAULT;
+
+	return 0;
+}
+
 /* Check whether the given kctl info is valid */
 static int snd_ctl_check_elem_info(struct snd_card *card,
 				   const struct snd_ctl_elem_info *info)
@@ -1703,7 +1715,7 @@ static long snd_ctl_ioctl(struct file *file, unsigned int cmd, unsigned long arg
 	case SNDRV_CTL_IOCTL_CARD_INFO:
 		return snd_ctl_card_info(card, ctl, cmd, argp);
 	case SNDRV_CTL_IOCTL_ELEM_LIST:
-		return snd_ctl_elem_list(card, argp);
+		return snd_ctl_elem_list_user(card, argp);
 	case SNDRV_CTL_IOCTL_ELEM_INFO:
 		return snd_ctl_elem_info_user(ctl, argp);
 	case SNDRV_CTL_IOCTL_ELEM_READ:

sound/core/control_compat.c

@@ -22,24 +22,22 @@ struct snd_ctl_elem_list32 {
 static int snd_ctl_elem_list_compat(struct snd_card *card,
 				    struct snd_ctl_elem_list32 __user *data32)
 {
-	struct snd_ctl_elem_list __user *data;
+	struct snd_ctl_elem_list data = {};
 	compat_caddr_t ptr;
 	int err;
 
-	data = compat_alloc_user_space(sizeof(*data));
-
 	/* offset, space, used, count */
-	if (copy_in_user(data, data32, 4 * sizeof(u32)))
+	if (copy_from_user(&data, data32, 4 * sizeof(u32)))
 		return -EFAULT;
 	/* pids */
-	if (get_user(ptr, &data32->pids) ||
-	    put_user(compat_ptr(ptr), &data->pids))
+	if (get_user(ptr, &data32->pids))
 		return -EFAULT;
-	err = snd_ctl_elem_list(card, data);
+	data.pids = compat_ptr(ptr);
+	err = snd_ctl_elem_list(card, &data);
 	if (err < 0)
 		return err;
 	/* copy the result */
-	if (copy_in_user(data32, data, 4 * sizeof(u32)))
+	if (copy_to_user(data32, &data, 4 * sizeof(u32)))
 		return -EFAULT;
 	return 0;
 }

sound/core/hwdep.c

@@ -203,28 +203,35 @@ static int snd_hwdep_dsp_status(struct snd_hwdep *hw,
 }
 
 static int snd_hwdep_dsp_load(struct snd_hwdep *hw,
-			      struct snd_hwdep_dsp_image __user *_info)
+			      struct snd_hwdep_dsp_image *info)
 {
-	struct snd_hwdep_dsp_image info;
 	int err;
 	
 	if (! hw->ops.dsp_load)
 		return -ENXIO;
-	memset(&info, 0, sizeof(info));
-	if (copy_from_user(&info, _info, sizeof(info)))
-		return -EFAULT;
-	if (info.index >= 32)
+	if (info->index >= 32)
 		return -EINVAL;
 	/* check whether the dsp was already loaded */
-	if (hw->dsp_loaded & (1u << info.index))
+	if (hw->dsp_loaded & (1u << info->index))
 		return -EBUSY;
-	err = hw->ops.dsp_load(hw, &info);
+	err = hw->ops.dsp_load(hw, info);
 	if (err < 0)
 		return err;
-	hw->dsp_loaded |= (1u << info.index);
+	hw->dsp_loaded |= (1u << info->index);
 	return 0;
 }
 
+static int snd_hwdep_dsp_load_user(struct snd_hwdep *hw,
+				   struct snd_hwdep_dsp_image __user *_info)
+{
+	struct snd_hwdep_dsp_image info = {};
+
+	if (copy_from_user(&info, _info, sizeof(info)))
+		return -EFAULT;
+	return snd_hwdep_dsp_load(hw, &info);
+}
+
+
 static long snd_hwdep_ioctl(struct file * file, unsigned int cmd,
 			    unsigned long arg)
 {
@@ -238,7 +245,7 @@ static long snd_hwdep_ioctl(struct file * file, unsigned int cmd,
 	case SNDRV_HWDEP_IOCTL_DSP_STATUS:
 		return snd_hwdep_dsp_status(hw, argp);
 	case SNDRV_HWDEP_IOCTL_DSP_LOAD:
-		return snd_hwdep_dsp_load(hw, argp);
+		return snd_hwdep_dsp_load_user(hw, argp);
 	}
 	if (hw->ops.ioctl)
 		return hw->ops.ioctl(hw, file, cmd, arg);

sound/core/hwdep_compat.c

@@ -19,26 +19,17 @@ struct snd_hwdep_dsp_image32 {
 static int snd_hwdep_dsp_load_compat(struct snd_hwdep *hw,
 				     struct snd_hwdep_dsp_image32 __user *src)
 {
-	struct snd_hwdep_dsp_image __user *dst;
+	struct snd_hwdep_dsp_image info = {};
 	compat_caddr_t ptr;
-	u32 val;
 
-	dst = compat_alloc_user_space(sizeof(*dst));
-
-	/* index and name */
-	if (copy_in_user(dst, src, 4 + 64))
-		return -EFAULT;
-	if (get_user(ptr, &src->image) ||
-	    put_user(compat_ptr(ptr), &dst->image))
-		return -EFAULT;
-	if (get_user(val, &src->length) ||
-	    put_user(val, &dst->length))
-		return -EFAULT;
-	if (get_user(val, &src->driver_data) ||
-	    put_user(val, &dst->driver_data))
+	if (copy_from_user(&info, src, 4 + 64) ||
+	    get_user(ptr, &src->image) ||
+	    get_user(info.length, &src->length) ||
+	    get_user(info.driver_data, &src->driver_data))
 		return -EFAULT;
+	info.image = compat_ptr(ptr);
 
-	return snd_hwdep_dsp_load(hw, dst);
+	return snd_hwdep_dsp_load(hw, &info);
 }
 
 enum {