hfsplus: fix worst-case unicode to char conversion of file names and attributes

This is a series of 3 patches which corrects issues in HFS+ concerning
the use of non-english file names and attributes. Names and attributes
are stored internally as UTF-16 units up to a fixed maximum size, and
convert to and from user-representation by NLS. The code incorrectly
assume that NLS string lengths are equal to unicode lengths, which is
only true for English ascii usage.

This patch (of 3):

The HFS Plus Volume Format specification (TN1150) states that file names
are stored internally as a maximum of 255 unicode characters, as defined
by The Unicode Standard, Version 2.0 [Unicode, Inc. ISBN
0-201-48345-9]. File names are converted by the NLS system on Linux
before presented to the user.

255 CJK characters converts to UTF-8 with 1 unicode character to up to 3
bytes, and to GB18030 with 1 unicode character to up to 4 bytes. Thus,
trying in a UTF-8 locale to list files with names of more than 85 CJK
characters results in:

$ ls /mnt
ls: reading directory /mnt: File name too long

The receiving buffer to hfsplus_uni2asc() needs to be 255 x
NLS_MAX_CHARSET_SIZE bytes, not 255 bytes as the code has always been.

Similar consideration applies to attributes, which are stored internally
as a maximum of 127 UTF-16BE units. See XNU source for an up-to-date
reference on attributes.

Strictly speaking, the maximum value of NLS_MAX_CHARSET_SIZE = 6 is not
attainable in the case of conversion to UTF-8, as going beyond 3 bytes
requires the use of surrogate pairs, i.e. consuming two input units.

Thanks Anton Altaparmakov for reviewing an earlier version of this
change.

This patch fixes all callers of hfsplus_uni2asc(), and also enables the
use of long non-English file names in HFS+. The getting and setting,
and general usage of long non-English attributes requires further
forthcoming work, in the following patches of this series.

[[e-mail]: fix build]
Signed-off-by: Hin-Tak Leung <[e-mail]>
Reviewed-by: Anton Altaparmakov <[e-mail]>
Cc: Vyacheslav Dubeyko <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Sougata Santra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/hfsplus/dir.c

···
 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/random.h>
+#include <linux/nls.h>
 
 #include "hfsplus_fs.h"
 #include "hfsplus_raw.h"
···
 	struct inode *inode = file_inode(file);
 	struct super_block *sb = inode->i_sb;
 	int len, err;
-	char strbuf[HFSPLUS_MAX_STRLEN + 1];
+	char *strbuf;
 	hfsplus_cat_entry entry;
 	struct hfs_find_data fd;
 	struct hfsplus_readdir_data *rd;
···
 	err = hfs_find_init(HFSPLUS_SB(sb)->cat_tree, &fd);
 	if (err)
 		return err;
+	strbuf = kmalloc(NLS_MAX_CHARSET_SIZE * HFSPLUS_MAX_STRLEN + 1, GFP_KERNEL);
+	if (!strbuf) {
+		err = -ENOMEM;
+		goto out;
+	}
 	hfsplus_cat_build_key(sb, fd.search_key, inode->i_ino, NULL);
 	err = hfs_brec_find(&fd, hfs_find_rec_by_key);
 	if (err)
···
 		hfs_bnode_read(fd.bnode, &entry, fd.entryoffset,
 			fd.entrylength);
 		type = be16_to_cpu(entry.type);
-		len = HFSPLUS_MAX_STRLEN;
+		len = NLS_MAX_CHARSET_SIZE * HFSPLUS_MAX_STRLEN;
 		err = hfsplus_uni2asc(sb, &fd.key->cat.name, strbuf, &len);
 		if (err)
 			goto out;
···
 	}
 	memcpy(&rd->key, fd.key, sizeof(struct hfsplus_cat_key));
 out:
+	kfree(strbuf);
 	hfs_find_exit(&fd);
 	return err;
 }

fs/hfsplus/xattr.c

···
 
 #include "hfsplus_fs.h"
 #include <linux/posix_acl_xattr.h>
+#include <linux/nls.h>
 #include "xattr.h"
 #include "acl.h"
 
···
 	struct hfs_find_data fd;
 	u16 key_len = 0;
 	struct hfsplus_attr_key attr_key;
-	char strbuf[HFSPLUS_ATTR_MAX_STRLEN +
-			XATTR_MAC_OSX_PREFIX_LEN + 1] = {0};
+	char *strbuf;
 	int xattr_name_len;
 
 	if ((!S_ISREG(inode->i_mode) &&
···
 	if (err) {
 		pr_err("can't init xattr find struct\n");
 		return err;
+	}
+
+	strbuf = kmalloc(NLS_MAX_CHARSET_SIZE * HFSPLUS_ATTR_MAX_STRLEN +
+			XATTR_MAC_OSX_PREFIX_LEN + 1, GFP_KERNEL);
+	if (!strbuf) {
+		res = -ENOMEM;
+		goto out;
 	}
 
 	err = hfsplus_find_attr(inode->i_sb, inode->i_ino, NULL, &fd);
···
 		if (be32_to_cpu(attr_key.cnid) != inode->i_ino)
 			goto end_listxattr;
 
-		xattr_name_len = HFSPLUS_ATTR_MAX_STRLEN;
+		xattr_name_len = NLS_MAX_CHARSET_SIZE * HFSPLUS_ATTR_MAX_STRLEN;
 		if (hfsplus_uni2asc(inode->i_sb,
 			(const struct hfsplus_unistr *)&fd.key->attr.key_name,
 					strbuf, &xattr_name_len)) {
···
 	}
 
 end_listxattr:
+	kfree(strbuf);
+out:
 	hfs_find_exit(&fd);
 	return res;
 }