[alsa-devel] [PATCH 12/24] ALSA: ctl: allocation of elem_info data for ELEM_INFO request

[Takashi Sakamoto]

In current implementation, for I/O request of ELEM_INFO, kernel stack
is used to copy 'struct snd_ctl_elem_info' data. However, the size of
this structure is a bit big and usage of kernel stack is not preferable.

This commit allocates a memory object on kernel space, instead.

Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
---
 sound/core/control.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index 8d158a49467d..4cb950e310bf 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -875,20 +875,23 @@ static int snd_ctl_elem_info(struct snd_ctl_file *ctl,
 	return result;
 }
 
-static int snd_ctl_elem_info_user(struct snd_ctl_file *ctl,
-				  struct snd_ctl_elem_info __user *_info)
+static int snd_ctl_elem_info_user(struct snd_ctl_file *ctl, void __user *arg)
 {
-	struct snd_ctl_elem_info info;
-	int result;
+	struct snd_ctl_elem_info *info;
+	int err;
 
-	if (copy_from_user(&info, _info, sizeof(info)))
-		return -EFAULT;
-	result = snd_ctl_elem_info(ctl, &info);
-	if (result < 0)
-		return result;
-	if (copy_to_user(_info, &info, sizeof(info)))
-		return -EFAULT;
-	return result;
+	info = memdup_user(arg, sizeof(*info));
+	if (IS_ERR(info))
+		return PTR_ERR(info);
+
+	err = snd_ctl_elem_info(ctl, info);
+	if (err >= 0) {
+		if (copy_to_user(arg, info, sizeof(*info)))
+			return -EFAULT;
+	}
+
+	kfree(info);
+	return err;
 }
 
 static int snd_ctl_elem_read(struct snd_card *card,
-- 
2.14.1