f2fs: support FS_IOC_{GET,SET}FSLABEL

Support two generic fs ioctls FS_IOC_{GET,SET}FSLABEL, letting
f2fs pass generic/492 testcase.

Fixes were made by Eric where:
 - f2fs: fix buffer overruns in FS_IOC_{GET, SET}FSLABEL
   utf16s_to_utf8s() and utf8s_to_utf16s() take the number of characters,
   not the number of bytes.

 - f2fs: fix copying too many bytes in FS_IOC_SETFSLABEL
   Userspace provides a null-terminated string, so don't assume that the
   full FSLABEL_MAX bytes can always be copied.

 - f2fs: add missing authorization check in FS_IOC_SETFSLABEL
   FS_IOC_SETFSLABEL modifies the filesystem superblock, so it shouldn't be
   allowed to regular users.  Require CAP_SYS_ADMIN, like xfs and btrfs do.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -418,6 +418,9 @@ static inline bool __has_cursum_space(struct f2fs_journal *journal,
 #define F2FS_IOC_PRECACHE_EXTENTS	_IO(F2FS_IOCTL_MAGIC, 15)
 #define F2FS_IOC_RESIZE_FS		_IOW(F2FS_IOCTL_MAGIC, 16, __u64)
 
+#define F2FS_IOC_GET_VOLUME_NAME	FS_IOC_GETFSLABEL
+#define F2FS_IOC_SET_VOLUME_NAME	FS_IOC_SETFSLABEL
+
 #define F2FS_IOC_SET_ENCRYPTION_POLICY	FS_IOC_SET_ENCRYPTION_POLICY
 #define F2FS_IOC_GET_ENCRYPTION_POLICY	FS_IOC_GET_ENCRYPTION_POLICY
 #define F2FS_IOC_GET_ENCRYPTION_PWSALT	FS_IOC_GET_ENCRYPTION_PWSALT

fs/f2fs/file.c

@@ -20,6 +20,7 @@
 #include <linux/uio.h>
 #include <linux/uuid.h>
 #include <linux/file.h>
+#include <linux/nls.h>
 
 #include "f2fs.h"
 #include "node.h"
@@ -3081,6 +3082,68 @@ static int f2fs_ioc_resize_fs(struct file *filp, unsigned long arg)
 	return ret;
 }
 
+static int f2fs_get_volume_name(struct file *filp, unsigned long arg)
+{
+	struct inode *inode = file_inode(filp);
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	char *vbuf;
+	int count;
+	int err = 0;
+
+	vbuf = f2fs_kzalloc(sbi, MAX_VOLUME_NAME, GFP_KERNEL);
+	if (!vbuf)
+		return -ENOMEM;
+
+	down_read(&sbi->sb_lock);
+	count = utf16s_to_utf8s(sbi->raw_super->volume_name,
+			ARRAY_SIZE(sbi->raw_super->volume_name),
+			UTF16_LITTLE_ENDIAN, vbuf, MAX_VOLUME_NAME);
+	up_read(&sbi->sb_lock);
+
+	if (copy_to_user((char __user *)arg, vbuf,
+				min(FSLABEL_MAX, count)))
+		err = -EFAULT;
+
+	kvfree(vbuf);
+	return err;
+}
+
+static int f2fs_set_volume_name(struct file *filp, unsigned long arg)
+{
+	struct inode *inode = file_inode(filp);
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	char *vbuf;
+	int err = 0;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	vbuf = strndup_user((const char __user *)arg, FSLABEL_MAX);
+	if (IS_ERR(vbuf))
+		return PTR_ERR(vbuf);
+
+	err = mnt_want_write_file(filp);
+	if (err)
+		goto out;
+
+	down_write(&sbi->sb_lock);
+
+	memset(sbi->raw_super->volume_name, 0,
+			sizeof(sbi->raw_super->volume_name));
+	utf8s_to_utf16s(vbuf, strlen(vbuf), UTF16_LITTLE_ENDIAN,
+			sbi->raw_super->volume_name,
+			ARRAY_SIZE(sbi->raw_super->volume_name));
+
+	err = f2fs_commit_super(sbi, false);
+
+	up_write(&sbi->sb_lock);
+
+	mnt_drop_write_file(filp);
+out:
+	kfree(vbuf);
+	return err;
+}
+
 long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	int ret;
@@ -3144,6 +3207,10 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return f2fs_ioc_precache_extents(filp, arg);
 	case F2FS_IOC_RESIZE_FS:
 		return f2fs_ioc_resize_fs(filp, arg);
+	case F2FS_IOC_GET_VOLUME_NAME:
+		return f2fs_get_volume_name(filp, arg);
+	case F2FS_IOC_SET_VOLUME_NAME:
+		return f2fs_set_volume_name(filp, arg);
 	default:
 		return -ENOTTY;
 	}
@@ -3253,6 +3320,8 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case F2FS_IOC_SET_PIN_FILE:
 	case F2FS_IOC_PRECACHE_EXTENTS:
 	case F2FS_IOC_RESIZE_FS:
+	case F2FS_IOC_GET_VOLUME_NAME:
+	case F2FS_IOC_SET_VOLUME_NAME:
 		break;
 	default:
 		return -ENOIOCTLCMD;