[PATCH v2 2/2] fat: Add FS_IOC_SETFSLABEL ioctl

[Ethan Ferguson]

Add support for writing to the volume label of a FAT filesystem via the
FS_IOC_SETFSLABEL ioctl.

Signed-off-by: Ethan Ferguson <ethan.ferguson@xxxxxxxxxx>
---
 fs/fat/dir.c         | 51 +++++++++++++++++++++++++++++++++++
 fs/fat/fat.h         |  6 +++++
 fs/fat/file.c        | 63 ++++++++++++++++++++++++++++++++++++++++++++
 fs/fat/inode.c       | 15 +++++++++++
 fs/fat/namei_msdos.c |  4 +--
 5 files changed, 137 insertions(+), 2 deletions(-)

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 07d95f1442c8..1b11713309ae 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -1425,3 +1425,54 @@ int fat_add_entries(struct inode *dir, void *slots, int nr_slots,
 	return err;
 }
 EXPORT_SYMBOL_GPL(fat_add_entries);
+
+static int fat_create_volume_label_dentry(struct super_block *sb, char *vol_label)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+	struct inode *root_inode = sb->s_root->d_inode;
+	struct msdos_dir_entry de;
+	struct fat_slot_info sinfo;
+	struct timespec64 ts = current_time(root_inode);
+	__le16 date, time;
+	u8 time_cs;
+
+	memcpy(de.name, vol_label, MSDOS_NAME);
+	de.attr = ATTR_VOLUME;
+	de.starthi = de.start = de.size = de.lcase = 0;
+
+	fat_time_unix2fat(sbi, &ts, &time, &date, &time_cs);
+	de.time = time;
+	de.date = date;
+	if (sbi->options.isvfat) {
+		de.cdate = de.adate = date;
+		de.ctime = time;
+		de.ctime_cs = time_cs;
+	} else
+		de.cdate = de.adate = de.ctime = de.ctime_cs = 0;
+
+	return fat_add_entries(root_inode, &de, 1, &sinfo);
+}
+
+int fat_rename_volume_label_dentry(struct super_block *sb, char *vol_label)
+{
+	struct inode *root_inode = sb->s_root->d_inode;
+	struct buffer_head *bh = NULL;
+	struct msdos_dir_entry *de;
+	loff_t cpos = 0;
+	int err = 0;
+
+	while (1) {
+		if (fat_get_entry(root_inode, &cpos, &bh, &de) == -1)
+			return fat_create_volume_label_dentry(sb, vol_label);
+
+		if (de->attr == ATTR_VOLUME) {
+			memcpy(de->name, vol_label, MSDOS_NAME);
+			mark_buffer_dirty_inode(bh, root_inode);
+			if (IS_DIRSYNC(root_inode))
+				err = sync_dirty_buffer(bh);
+			brelse(bh);
+			return err;
+		}
+	}
+}
+EXPORT_SYMBOL_GPL(fat_rename_volume_label_dentry);
diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 4350c00dba34..3b75223fbe76 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -341,6 +341,8 @@ extern int fat_alloc_new_dir(struct inode *dir, struct timespec64 *ts);
 extern int fat_add_entries(struct inode *dir, void *slots, int nr_slots,
 			   struct fat_slot_info *sinfo);
 extern int fat_remove_entries(struct inode *dir, struct fat_slot_info *sinfo);
+extern int fat_rename_volume_label_dentry(struct super_block *sb,
+					  char *vol_label);
 
 /* fat/fatent.c */
 struct fat_entry {
@@ -480,6 +482,10 @@ extern int fat_sync_bhs(struct buffer_head **bhs, int nr_bhs);
 int fat_cache_init(void);
 void fat_cache_destroy(void);
 
+/* fat/namei/msdos.c */
+int msdos_format_name(const unsigned char *name, int len,
+		      unsigned char *res, struct fat_mount_options *opts);
+
 /* fat/nfs.c */
 extern const struct export_operations fat_export_ops;
 extern const struct export_operations fat_export_ops_nostale;
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 029b1750d1ec..5d445c2d8657 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -167,6 +167,67 @@ static int fat_ioctl_get_volume_label(struct super_block *sb, char __user *arg)
 	return 0;
 }
 
+static int fat_convert_volume_label_str(struct msdos_sb_info *sbi, char *in,
+					char *out)
+{
+	int ret, in_len = max(strnlen(in, FSLABEL_MAX), 11);
+	char *needle;
+
+	/*
+	 * '.' is not included in any bad_chars list in this driver,
+	 * but it is specifically not allowed for volume labels
+	 */
+	for (needle = in; needle - in < in_len; needle++)
+		if (*needle == '.')
+			return -EINVAL;
+
+	ret = msdos_format_name(in, in_len, out, &sbi->options);
+	if (ret)
+		return ret;
+
+	/*
+	 * msdos_format_name assumes we're translating an 8.3 name, but
+	 * we can handle 11 chars
+	 */
+	if (in_len > 8)
+		ret = msdos_format_name(in + 8, in_len - 8, out + 8,
+					&sbi->options);
+	return ret;
+}
+
+static int fat_ioctl_set_volume_label(struct super_block *sb, char __user *arg)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+	struct inode *root_inode = sb->s_root->d_inode;
+	char from_user[FSLABEL_MAX];
+	char new_vol_label[MSDOS_NAME];
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (sb_rdonly(sb))
+		return -EROFS;
+
+	if (copy_from_user(from_user, arg, FSLABEL_MAX))
+		return -EFAULT;
+
+	ret = fat_convert_volume_label_str(sbi, from_user, new_vol_label);
+	if (ret)
+		return ret;
+
+	inode_lock(root_inode);
+	ret = fat_rename_volume_label_dentry(sb, new_vol_label);
+	inode_unlock(root_inode);
+	if (ret)
+		return ret;
+
+	mutex_lock(&sbi->s_lock);
+	memcpy(sbi->vol_label, new_vol_label, MSDOS_NAME);
+	mutex_unlock(&sbi->s_lock);
+	return 0;
+}
+
 long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -181,6 +242,8 @@ long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return fat_ioctl_get_volume_id(inode, user_attr);
 	case FS_IOC_GETFSLABEL:
 		return fat_ioctl_get_volume_label(inode->i_sb, (char __user *) arg);
+	case FS_IOC_SETFSLABEL:
+		return fat_ioctl_set_volume_label(inode->i_sb, (char __user *) arg);
 	case FITRIM:
 		return fat_ioctl_fitrim(inode, arg);
 	default:
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 6f9a8cc1ad2a..a7528937383b 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -736,6 +736,21 @@ static void delayed_free(struct rcu_head *p)
 static void fat_put_super(struct super_block *sb)
 {
 	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+	struct buffer_head *bh = NULL;
+	struct fat_boot_sector *bs;
+
+	bh = sb_bread(sb, 0);
+	if (bh == NULL)
+		fat_msg(sb, KERN_ERR, "unable to read boot sector");
+	else if (!sb_rdonly(sb)) {
+		bs = (struct fat_boot_sector *)bh->b_data;
+		if (is_fat32(sbi))
+			memcpy(bs->fat32.vol_label, sbi->vol_label, MSDOS_NAME);
+		else
+			memcpy(bs->fat16.vol_label, sbi->vol_label, MSDOS_NAME);
+		mark_buffer_dirty(bh);
+	}
+	brelse(bh);
 
 	fat_set_state(sb, 0, 0);
 
diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index ba0152ed0810..92b5d387f88e 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -16,8 +16,8 @@ static unsigned char bad_chars[] = "*?<>|\"";
 static unsigned char bad_if_strict[] = "+=,; ";
 
 /***** Formats an MS-DOS file name. Rejects invalid names. */
-static int msdos_format_name(const unsigned char *name, int len,
-			     unsigned char *res, struct fat_mount_options *opts)
+int msdos_format_name(const unsigned char *name, int len, unsigned char *res,
+		      struct fat_mount_options *opts)
 	/*
 	 * name is the proposed name, len is its length, res is
 	 * the resulting name, opts->name_check is either (r)elaxed,
-- 
2.43.0