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From 90c504b1911b52eb917860195f849eddb8fff7c4 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Tue, 21 Jul 2009 09:59:29 +1000
Subject: [PATCH] FAT: Add CONFIG_VFAT_FS_NO_DUALNAMES option
This patch adds a new config option VFAT_FS_NO_DUALNAMES. When
VFAT_FS_NO_DUALNAMES is enabled, VFAT will never create a file with
both a long and a short filename. If a long filename is needed, then
dummy bytes are stored in the 8.3 entry, and the 8.3 entry is marked
as having no short name using the FAT_NO_83NAME flag.
Signed-off-by: Andrew Tridgell <tridge@samba.org>
---
fs/fat/Kconfig | 21 ++++++++++++++
fs/fat/namei_vfat.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 102 insertions(+), 2 deletions(-)
diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig
index 3ff1772f612e..1f103d835e8c 100644
--- a/fs/fat/Kconfig
+++ b/fs/fat/Kconfig
@@ -74,6 +74,27 @@ config VFAT_FS
To compile this as a module, choose M here: the module will be called
vfat.
+config VFAT_FS_NO_DUALNAMES
+ bool "disable VFAT dual names support (patent workaround)"
+ depends on VFAT_FS
+ help
+ This option disables support for dual filenames on VFAT filesystems.
+ If this option is enabled then file creation will either put
+ a short (8.3) name or a long name on the file, but never both.
+ The field where a shortname would normally go is filled with
+ invalid characters such that it cannot be considered a valid
+ short filename.
+
+ That means that long filenames created with this option
+ disabled will not be accessible at all to operating systems
+ that do not understand the FAT long filename extensions.
+
+ Users considering disabling this option should consider the
+ implications of any patents that may exist on dual filenames
+ in VFAT.
+
+ If unsure, say N
+
config FAT_DEFAULT_CODEPAGE
int "Default codepage for FAT"
depends on MSDOS_FS || VFAT_FS
diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 2649759c478a..a5c3b6cd435a 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -21,6 +21,7 @@
#include <linux/namei.h>
#include <linux/kernel.h>
#include <linux/iversion.h>
+#include <linux/random.h>
#include "fat.h"
static inline unsigned long vfat_d_version(struct dentry *dentry)
@@ -335,6 +336,17 @@ static int vfat_create_shortname(struct inode *dir, struct nls_table *nls,
int sz = 0, extlen, baselen, i, numtail_baselen, numtail2_baselen;
int is_shortname;
struct shortname_info base_info, ext_info;
+ unsigned opts_shortname = opts->shortname;
+
+#ifdef CONFIG_VFAT_FS_NO_DUALNAMES
+ /*
+ * When we do not have dualnames, we want to maximise the
+ * chance that a file will be able to be represented with just
+ * a 8.3 entry. We can do that by using the WINNT case
+ * handling extensions to FAT.
+ */
+ opts_shortname = VFAT_SFN_CREATE_WINNT;
+#endif
is_shortname = 1;
INIT_SHORTNAME_INFO(&base_info);
@@ -447,9 +459,9 @@ static int vfat_create_shortname(struct inode *dir, struct nls_table *nls,
if (vfat_find_form(dir, name_res) == 0)
return -EEXIST;
- if (opts->shortname & VFAT_SFN_CREATE_WIN95) {
+ if (opts_shortname & VFAT_SFN_CREATE_WIN95) {
return (base_info.upper && ext_info.upper);
- } else if (opts->shortname & VFAT_SFN_CREATE_WINNT) {
+ } else if (opts_shortname & VFAT_SFN_CREATE_WINNT) {
if ((base_info.upper || base_info.lower) &&
(ext_info.upper || ext_info.lower)) {
if (!base_info.upper && base_info.lower)
@@ -575,6 +587,66 @@ xlate_to_uni(const unsigned char *name, int len, unsigned char *outname,
return 0;
}
+#ifdef CONFIG_VFAT_FS_NO_DUALNAMES
+/*
+ * This function creates a dummy 8.3 entry which is as compatible as
+ * possible with existing FAT devices, while not being a valid
+ * filename under windows or Linux
+ */
+static void vfat_build_dummy_83_buffer(struct inode *dir, char *msdos_name,
+ int is_dir)
+{
+ /*
+ * These characters are all invalid in 8.3 names, plus have
+ * been shown to be harmless on all tested devices
+ */
+ const char invalidchar[] = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x0B,
+ 0x0C, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13,
+ 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A,
+ 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x22, 0x2a,
+ 0x3a, 0x3c, 0x3e, 0x3f, 0x5b, 0x5d, 0x7c };
+ int i, tilde_pos, slash_pos;
+ u32 rand_num = random32();
+
+ /* We need a '~' in the prefix to make Win98 happy. */
+ tilde_pos = rand_num % 8;
+ rand_num >>= 3;
+
+ /*
+ * the '/' makes sure that even unpatched Linux systems can't
+ * get at files by the 8.3 entry. Don't put in a / in
+ * directories as it can cause problems with some
+ * photo frames
+ */
+ if (is_dir)
+ slash_pos = -1;
+ else {
+ slash_pos = (tilde_pos + 1 + rand_num % 7) % 8;
+ rand_num >>= 3;
+ }
+
+ /*
+ * fill in the first 8 bytes with invalid characters. Note
+ * that we need to be careful not to run out of randomness. We
+ * leave the 3 byte extension in place as some cheap MP3
+ * players need them.
+ */
+ for (i = 0; i < 8; i++) {
+ if (i == tilde_pos)
+ msdos_name[i] = '~';
+ else if (i == slash_pos)
+ msdos_name[i] = '/';
+ else {
+ msdos_name[i] =
+ invalidchar[rand_num % sizeof(invalidchar)];
+ rand_num /= sizeof(invalidchar);
+ if (rand_num < sizeof(invalidchar))
+ rand_num = random32();
+ }
+ }
+}
+#endif
+
static int vfat_build_slots(struct inode *dir, const unsigned char *name,
int len, int is_dir, int cluster,
struct timespec *ts,
@@ -617,6 +689,13 @@ static int vfat_build_slots(struct inode *dir, const unsigned char *name,
goto shortname;
}
+#ifdef CONFIG_VFAT_FS_NO_DUALNAMES
+ printk_once(KERN_INFO
+ "VFAT: not creating 8.3 short filenames for long names\n");
+ vfat_build_dummy_83_buffer(dir, msdos_name, is_dir);
+ lcase = FAT_NO_83NAME;
+#endif
+
/* build the entry of long file name */
cksum = fat_checksum(msdos_name);
--
2.5.0
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