exfat currently unconditionally strips trailing
periods '.' when performing path lookup, but allows them in the filenames
during file creation. This is done intentionally, loosely following Windows
behaviour and specifications which state:
#exFAT
The concatenated file name has the same set of illegal characters as
other FAT-based file systems (see Table 31).
#FAT
...
Leading and trailing spaces in a long name are ignored.
Leading and embedded periods are allowed in a name and are stored in
the long name. Trailing periods are ignored.
Note: Leading and trailing space ' ' characters are currently retained
by Linux kernel exfat, in conflict with the above specification.
On Windows 10, File Explore application retains leading and trailing
space characters. But on the commandline behavior was exactly the opposite.
Some implementations, such as fuse-exfat, don't perform path trailer
removal. When mounting images which contain trailing-dot paths, these
paths are unreachable, e.g.:
+ mount.exfat-fuse /dev/zram0 /mnt/test/
FUSE exfat 1.3.0
+ cd /mnt/test/
+ touch fuse_created_dots... ' fuse_created_spaces '
+ ls -l
total 0
-rwxrwxrwx 1 root 0 0 Aug 18 09:45 ' fuse_created_spaces '
-rwxrwxrwx 1 root 0 0 Aug 18 09:45 fuse_created_dots...
+ cd /
+ umount /mnt/test/
+ mount -t exfat /dev/zram0 /mnt/test
+ cd /mnt/test
+ ls -l
ls: cannot access 'fuse_created_dots...': No such file or directory
total 0
-rwxr-xr-x 1 root 0 0 Aug 18 09:45 ' fuse_created_spaces '
-????????? ? ? ? ? ? fuse_created_dots...
+ touch kexfat_created_dots... ' kexfat_created_spaces '
+ ls -l
ls: cannot access 'fuse_created_dots...': No such file or directory
total 0
-rwxr-xr-x 1 root 0 0 Aug 18 09:45 ' fuse_created_spaces '
-rwxr-xr-x 1 root 0 0 Aug 18 09:45 ' kexfat_created_spaces '
-????????? ? ? ? ? ? fuse_created_dots...
-rwxr-xr-x 1 root 0 0 Aug 18 09:45 kexfat_created_dots
+ cd /
+ umount /mnt/test/
With this change, the "keep_last_dots" mount option can be used to access
paths with trailing periods and disallow creating files with names with
trailing periods. E.g. continuing from the previous example:
+ mount -t exfat -o keep_last_dots /dev/zram0 /mnt/test
+ cd /mnt/test
+ ls -l
total 0
-rwxr-xr-x 1 root 0 0 Aug 18 10:32 ' fuse_created_spaces '
-rwxr-xr-x 1 root 0 0 Aug 18 10:32 ' kexfat_created_spaces '
-rwxr-xr-x 1 root 0 0 Aug 18 10:32 fuse_created_dots...
-rwxr-xr-x 1 root 0 0 Aug 18 10:32 kexfat_created_dots
+ echo > kexfat_created_dots_again...
sh: kexfat_created_dots_again...: Invalid argument
Link: https://bugzilla.suse.com/show_bug.cgi?id=1188964
Link: https://lore.kernel.org/linux-fsdevel/003b01d755e4$31fb0d80$95f12880$
@samsung.com/
Link: https://docs.microsoft.com/en-us/windows/win32/fileio/exfat-specification
Suggested-by: Takashi Iwai <[email protected]>
Signed-off-by: Vasant Karasulli <[email protected]>
Co-developed-by: David Disseldorp <[email protected]>
Signed-off-by: David Disseldorp <[email protected]>
---
fs/exfat/namei.c | 50 ++++++++++++++++++++++++++++++++++--------------
1 file changed, 36 insertions(+), 14 deletions(-)
diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index af4eb39cc0c3..a4f8010fbd38 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -65,11 +65,14 @@ static int exfat_d_revalidate(struct dentry *dentry, unsigned int flags)
return ret;
}
-/* returns the length of a struct qstr, ignoring trailing dots */
-static unsigned int exfat_striptail_len(unsigned int len, const char *name)
+/* returns the length of a struct qstr, ignoring trailing dots if necessary */
+static unsigned int exfat_striptail_len(unsigned int len, const char *name,
+ bool keep_last_dots)
{
- while (len && name[len - 1] == '.')
- len--;
+ if (!keep_last_dots) {
+ while (len && name[len - 1] == '.')
+ len--;
+ }
return len;
}
@@ -83,7 +86,8 @@ static int exfat_d_hash(const struct dentry *dentry, struct qstr *qstr)
struct super_block *sb = dentry->d_sb;
struct nls_table *t = EXFAT_SB(sb)->nls_io;
const unsigned char *name = qstr->name;
- unsigned int len = exfat_striptail_len(qstr->len, qstr->name);
+ unsigned int len = exfat_striptail_len(qstr->len, qstr->name,
+ EXFAT_SB(sb)->options.keep_last_dots);
unsigned long hash = init_name_hash(dentry);
int i, charlen;
wchar_t c;
@@ -104,8 +108,10 @@ static int exfat_d_cmp(const struct dentry *dentry, unsigned int len,
{
struct super_block *sb = dentry->d_sb;
struct nls_table *t = EXFAT_SB(sb)->nls_io;
- unsigned int alen = exfat_striptail_len(name->len, name->name);
- unsigned int blen = exfat_striptail_len(len, str);
+ unsigned int alen = exfat_striptail_len(name->len, name->name,
+ EXFAT_SB(sb)->options.keep_last_dots);
+ unsigned int blen = exfat_striptail_len(len, str,
+ EXFAT_SB(sb)->options.keep_last_dots);
wchar_t c1, c2;
int charlen, i;
@@ -136,7 +142,8 @@ static int exfat_utf8_d_hash(const struct dentry *dentry, struct qstr *qstr)
{
struct super_block *sb = dentry->d_sb;
const unsigned char *name = qstr->name;
- unsigned int len = exfat_striptail_len(qstr->len, qstr->name);
+ unsigned int len = exfat_striptail_len(qstr->len, qstr->name,
+ EXFAT_SB(sb)->options.keep_last_dots);
unsigned long hash = init_name_hash(dentry);
int i, charlen;
unicode_t u;
@@ -161,8 +168,11 @@ static int exfat_utf8_d_cmp(const struct dentry *dentry, unsigned int len,
const char *str, const struct qstr *name)
{
struct super_block *sb = dentry->d_sb;
- unsigned int alen = exfat_striptail_len(name->len, name->name);
- unsigned int blen = exfat_striptail_len(len, str);
+ unsigned int alen = exfat_striptail_len(name->len, name->name,
+ EXFAT_SB(sb)->options.keep_last_dots);
+ unsigned int blen = exfat_striptail_len(len, str,
+ EXFAT_SB(sb)->options.keep_last_dots);
+
unicode_t u_a, u_b;
int charlen, i;
@@ -416,13 +426,25 @@ static int __exfat_resolve_path(struct inode *inode, const unsigned char *path,
struct super_block *sb = inode->i_sb;
struct exfat_sb_info *sbi = EXFAT_SB(sb);
struct exfat_inode_info *ei = EXFAT_I(inode);
+ int pathlen = strlen(path);
- /* strip all trailing periods */
- namelen = exfat_striptail_len(strlen(path), path);
+ /*
+ * get the length of the pathname excluding
+ * trailing periods, if any.
+ */
+ namelen = exfat_striptail_len(pathlen, path, false);
+ if (EXFAT_SB(sb)->options.keep_last_dots) {
+ /*
+ * Do not allow the creation of files with names
+ * ending with period(s).
+ */
+ if (!lookup && (namelen < pathlen))
+ return -EINVAL;
+ namelen = pathlen;
+ }
if (!namelen)
return -ENOENT;
-
- if (strlen(path) > (MAX_NAME_LENGTH * MAX_CHARSET_SIZE))
+ if (pathlen > (MAX_NAME_LENGTH * MAX_CHARSET_SIZE))
return -ENAMETOOLONG;
/*
--
2.32.0
Hi Vasant,
A couple of things I missed in the previous round...
On Fri, 11 Mar 2022 12:47:46 +0100, Vasant Karasulli wrote:
> exfat currently unconditionally strips trailing
> periods '.' when performing path lookup, but allows them in the filenames
> during file creation.
Trailing periods *are* currently stripped during creation, so that
statement should be removed, e.g.
The Linux kernel exfat driver currently unconditionally strips
trailing periods '.' from path components.
> This is done intentionally, loosely following Windows
> behaviour and specifications which state:
>
> #exFAT
> The concatenated file name has the same set of illegal characters as
> other FAT-based file systems (see Table 31).
>
> #FAT
> ...
> Leading and trailing spaces in a long name are ignored.
> Leading and embedded periods are allowed in a name and are stored in
> the long name. Trailing periods are ignored.
>
> Note: Leading and trailing space ' ' characters are currently retained
> by Linux kernel exfat, in conflict with the above specification.
> On Windows 10, File Explore application retains leading and trailing
> space characters. But on the commandline behavior was exactly the opposite.
As mentioned earlier, my observations from Windows10 CopyFile() win32
API calls were that trailing spaces and periods are stripped. AFAICT
that's also the case for Windows Explorer and cmd.exe paths.
Cheers, David