ntfs3: fix use-after-free of sbi->options in cmp_fnames

The root cause is that sbi->options points directly to fc->fs_private.
If fc->fs_private is freed while sbi still exists, sbi->options becomes
a dangling pointer.

This patch ensures that sbi->options is a separate copy of fc->fs_private
and duplicates nls_name if present. On superblock release or error,
sbi->options->nls_name and sbi->options are freed and sbi->options
is set to NULL to avoid any dangling pointer.

Reported-by: syzbot+d77c546c60db651a389c@syzkaller.appspotmail.com
Signed-off-by: YangWen <anmuxixixi@gmail.com>
[almaz.alexandrovich@paragon-software.com: remove syzbot logs from description]
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: anmuxixixi

fs/ntfs3/super.c

@@ -702,6 +702,14 @@ static void ntfs_put_super(struct super_block *sb)
 
 	/* Mark rw ntfs as clear, if possible. */
 	ntfs_set_state(sbi, NTFS_DIRTY_CLEAR);
+
+	if (sbi->options) {
+		unload_nls(sbi->options->nls);
+		kfree(sbi->options->nls);
+		kfree(sbi->options);
+		sbi->options = NULL;
+	}
+
 	ntfs3_put_sbi(sbi);
 }
 
@@ -1203,7 +1211,8 @@ static int ntfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	int err;
 	struct ntfs_sb_info *sbi = sb->s_fs_info;
 	struct block_device *bdev = sb->s_bdev;
-	struct ntfs_mount_options *options;
+	struct ntfs_mount_options *fc_opts;
+	struct ntfs_mount_options *options = NULL;
 	struct inode *inode;
 	struct ntfs_inode *ni;
 	size_t i, tt, bad_len, bad_frags;
@@ -1220,20 +1229,35 @@ static int ntfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	ref.high = 0;
 
 	sbi->sb = sb;
-	sbi->options = options = fc->fs_private;
-	fc->fs_private = NULL;
+	fc_opts = fc->fs_private;
+	if (!fc_opts) {
+		errorf(fc, "missing mount options");
+		return -EINVAL;
+	}
+	options = kmemdup(fc_opts, sizeof(*fc_opts), GFP_KERNEL);
+	if (!options)
+		return -ENOMEM;
+
+	if (fc_opts->nls_name) {
+		options->nls_name = kstrdup(fc_opts->nls_name, GFP_KERNEL);
+		if (!options->nls_name) {
+			kfree(options);
+			return -ENOMEM;
+		}
+	}
+	sbi->options = options;
 	sb->s_flags |= SB_NODIRATIME;
 	sb->s_magic = 0x7366746e; // "ntfs"
 	sb->s_op = &ntfs_sops;
 	sb->s_export_op = &ntfs_export_ops;
 	sb->s_time_gran = NTFS_TIME_GRAN; // 100 nsec
 	sb->s_xattr = ntfs_xattr_handlers;
-	set_default_d_op(sb, options->nocase ? &ntfs_dentry_ops : NULL);
+	set_default_d_op(sb, sbi->options->nocase ? &ntfs_dentry_ops : NULL);
 
-	options->nls = ntfs_load_nls(options->nls_name);
-	if (IS_ERR(options->nls)) {
-		options->nls = NULL;
-		errorf(fc, "Cannot load nls %s", options->nls_name);
+	sbi->options->nls = ntfs_load_nls(sbi->options->nls_name);
+	if (IS_ERR(sbi->options->nls)) {
+		sbi->options->nls = NULL;
+		errorf(fc, "Cannot load nls %s", fc_opts->nls_name);
 		err = -EINVAL;
 		goto out;
 	}
@@ -1645,6 +1669,13 @@ static int ntfs_fill_super(struct super_block *sb, struct fs_context *fc)
 put_inode_out:
 	iput(inode);
 out:
+	if (sbi && sbi->options) {
+		unload_nls(sbi->options->nls);
+		kfree(sbi->options->nls);
+		kfree(sbi->options);
+		sbi->options = NULL;
+	}
+
 	ntfs3_put_sbi(sbi);
 	kfree(boot2);
 	return err;