This is the first of two patches which attempt to address the
technical concerns raised by the previous round of VFAT patent
workaround patches.
This patch adds a new flag field 'FAT_NO_83NAME' for FAT files. When
this flag is set on an 8.3 FAT entry, both the MSDOS and VFAT
filesystems will skip the entry. For MSDOS this makes the file
inaccessible. For VFAT it makes the file only accessible by the long
filename.
The justification for this patch is to provide a clean way to
distinguish files created on VFAT filesystems with long filenames but
without a 8.3 short name. It uses a unused bit in the FAT directory
entry to store the FAT_NO_83NAME flag.
This patch, combined with the following VFAT_FS_NO_DUALNAMES patch,
address the following technical issues found with the last series of
patches:
- Fixed problems with Win98, although some cosmetic issues remain
- Fixed problems with all tested MP3 players and similar devices
- Lowers the probability of a WinXP bluescreen by a factor of about 80x
- Fixed problems with mtools, although some cosmetic issues remain
that require a small mtools patch to fix
More details and testing tools are available at
http://kernel.org/pub/linux/kernel/people/tridge/VFAT/
Signed-off-by: Andrew Tridgell <[email protected]>
---
fs/fat/dir.c | 14 ++++++++++++++
include/linux/msdos_fs.h | 1 +
2 files changed, 15 insertions(+), 0 deletions(-)
diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 38ff75a..902e84c 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -385,6 +385,13 @@ parse_record:
goto end_of_dir;
}
+ /*
+ * The FAT_NO_83NAME flag is used to mark files
+ * created with no 8.3 short name
+ */
+ if (de->lcase & FAT_NO_83NAME)
+ goto compare_longname;
+
memcpy(work, de->name, sizeof(de->name));
/* see namei.c, msdos_format_name */
if (work[0] == 0x05)
@@ -429,6 +436,7 @@ parse_record:
if (fat_name_match(sbi, name, name_len, bufname, len))
goto found;
+compare_longname:
if (nr_slots) {
void *longname = unicode + FAT_MAX_UNI_CHARS;
int size = PATH_MAX - FAT_MAX_UNI_SIZE;
@@ -530,6 +538,8 @@ parse_record:
if (de->attr != ATTR_EXT && IS_FREE(de->name))
goto record_end;
} else {
+ if (de->lcase & FAT_NO_83NAME)
+ goto record_end;
if ((de->attr & ATTR_VOLUME) || IS_FREE(de->name))
goto record_end;
}
@@ -935,6 +945,10 @@ int fat_scan(struct inode *dir, const unsigned char *name,
sinfo->bh = NULL;
while (fat_get_short_entry(dir, &sinfo->slot_off, &sinfo->bh,
&sinfo->de) >= 0) {
+ /* skip files marked as having no 8.3 short name */
+ if (sinfo->de->lcase & FAT_NO_83NAME)
+ continue;
+
if (!strncmp(sinfo->de->name, name, MSDOS_NAME)) {
sinfo->slot_off -= sizeof(*sinfo->de);
sinfo->nr_slots = 1;
diff --git a/include/linux/msdos_fs.h b/include/linux/msdos_fs.h
index ce38f1c..639e6a4 100644
--- a/include/linux/msdos_fs.h
+++ b/include/linux/msdos_fs.h
@@ -43,6 +43,7 @@
#define CASE_LOWER_BASE 8 /* base is lower case */
#define CASE_LOWER_EXT 16 /* extension is lower case */
+#define FAT_NO_83NAME 32 /* no 8.3 short filename for this file */
#define DELETED_FLAG 0xe5 /* marks file as deleted when in name[0] */
#define IS_FREE(n) (!*(n) || *(n) == DELETED_FLAG)
--
1.6.0.4
This is the second of two patches which attempt to address the
technical concerns raised by the previous round of VFAT patent
workaround patches.
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.
This patch is similar in concept to the previously posted dualnames
patch, but changes the bytes put in the 8.3 directory entry when long
filenames are created. The new values work with Win98, MP3 players and
other devices that have been tested.
This patch depends on the FAT_NO_83NAME flag added in the first patch
in this series.
More details and testing tools are available at
http://kernel.org/pub/linux/kernel/people/tridge/VFAT/
Signed-off-by: Andrew Tridgell <[email protected]>
---
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 182f9ff..d1c10a1 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 73471b7..02d5d64 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -22,6 +22,7 @@
#include <linux/smp_lock.h>
#include <linux/buffer_head.h>
#include <linux/namei.h>
+#include <linux/random.h>
#include "fat.h"
/*
@@ -316,6 +317,17 @@ 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);
@@ -428,9 +440,9 @@ 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)
@@ -586,6 +598,66 @@ 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,
@@ -628,6 +700,13 @@ 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);
--
1.6.0.4