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From:   Namjae Jeon <linkinjeon@kernel.org>
Date:   Thu, 17 Mar 2022 22:30:28 +0900
Message-ID: <CAKYAXd-BZgy-gVAPhLhGNc31q-+8t18A=ho_Q6STmEBoGCoW0w@mail.gmail.com>
Subject: Re: [PATCH v5 1/1] exfat: allow access to paths with trailing dots
To:     Vasant Karasulli <vkarasulli@suse.de>
Cc:     David Disseldorp <ddiss@suse.de>, linux-fsdevel@vger.kernel.org,
        Sungjong Seo <sj1557.seo@samsung.com>,
        linux-kernel@vger.kernel.org, Takashi Iwai <tiwai@suse.de>
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2022-03-17 18:50 GMT+09:00, Vasant Karasulli <vkarasulli@suse.de>:
>  The Linux kernel exfat driver currently unconditionally strips
>  trailing periods '.' from path components. This isdone 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, trailing and leading space ' ' characters are stripped
> from the filenames.
> 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/
>
> This commit adds "keep_last_dots" mount option that controls whether or
> not trailing periods '.' are stripped
> from path components during file lookup or file creation.
> This 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 <tiwai@suse.de>
> Signed-off-by: Vasant Karasulli <vkarasulli@suse.de>
> Co-developed-by: David Disseldorp <ddiss@suse.de>
> Signed-off-by: David Disseldorp <ddiss@suse.de>
Applied, Thanks for your patch!