From: "koraynilay" <koray.fra@gmail.com>
To: "Namjae Jeon" <linkinjeon@kernel.org>,
"koraynilay" <koray.fra@gmail.com>
Cc: "Sergey Senozhatsky" <senozhatsky@chromium.org>,
"Tom Talpey" <tom@talpey.com>,
"ChenXiaoSong" <chenxiaosong@chenxiaosong.com>,
"Hyunchul Lee" <hyc.lee@gmail.com>, <linux-cifs@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ksmbd: decode and honor DOS attribute validity flags
Date: Sat, 14 Nov 2026 01:58:45 +0100 [thread overview]
Message-ID: <DMUIYLA1N1WI.58082D8BPB0T@gmail.com> (raw)
In-Reply-To: <CAKYAXd-X_u1CapKjpLPJF+ecUo5LN15Zj9T8bLguhyYWY7YrWQ@mail.gmail.com>
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On Sat Nov 14, 2026 at 1:26 AM CET, Namjae Jeon wrote:
> On Sat, Nov 14, 2026 at 7:16 AM koraynilay <koray.fra@gmail.com> wrote:
>>
>> Currently, when setting file attributes via FSCTL_SET_SPARSE,
>> FSCTL_SET_COMPRESSION or FileBasicInformation, ksmbd hardcodes
>> flags = 0x51 (XATTR_DOSINFO_ATTRIB | XATTR_DOSINFO_CREATE_TIME |
>> XATTR_DOSINFO_ITIME). This injects unrequested creation time and itime
>> into user.DOSATTRIB on disk, even though the client only requested an
>> attribute modification.
>>
>> Furthermore, ndr_decode_dos_attr() discards the validity flags on read
>> by reading them into NULL. When reading a file with an attribute-only
>> xattr (flags = 0x01, where create_time on disk is 0), ksmbd treats the 0
>> as a valid timestamp and reports NTTIME(0) instead of falling back to
>> the underlying filesystem's btime. Modifying any attribute via
>> set_file_basic_info() then clobbers the xattr back to 0x51.
>>
>> Fix this by:
>> 1. decoding da->flags in ndr_decode_dos_attr() and only updating
>> create_time and itime if their validity flags are set (in
>> smb2_update_xattrs() and ksmbd_vfs_fill_dentry_attrs());
>> 2. reading existing attributes and only setting XATTR_DOSINFO_ATTRIB in
>> fsctl_set_sparse(), __ksmbd_vfs_set_compression(), and
>> set_file_basic_info() so unrequested timestamps are not injected.
>>
>> Reproducer, with /tmp as the local filesystem folder exported as [test]
>> in ksmbd.conf and /mnt as the smb folder mounted with mount -t cifs:
>>
>> mount -t cifs //127.0.0.1/test /mnt -o username=user,password=pass
>>
>> test with sparse (for compression, use chattr +c instead of fallocate):
>>
>> echo data > /tmp/sparse.txt
>> chmod 777 /tmp/sparse.txt
>>
>> stat -c 'Local btime (%n): %w' /tmp/sparse.txt
>> getfattr -n user.DOSATTRIB -e hex /tmp/sparse.txt
>>
>> # punching hole via CIFS triggers FSCTL_SET_SPARSE
>> fallocate -p -o 0 -l 4 /mnt/sparse.txt
>> getfattr -n user.DOSATTRIB -e hex /tmp/sparse.txt
>>
>> stat -c 'CIFS btime (%n): %w' /mnt/sparse.txt
>> smbclient //127.0.0.1/test -U user%pass -c 'allinfo sparse.txt'
>>
>> # evict cache so btime is read fresh again
>> umount /mnt
>> mount -t cifs //127.0.0.1/test /mnt -o username=user,password=pass
>> stat -c 'CIFS btime (%n): %w' /mnt/sparse.txt
>>
>> which prints:
>>
>> Local btime (/tmp/sparse.txt): 2026-11-13 21:13:27.167926440 +0000
>> /tmp/sparse.txt: user.DOSATTRIB: No such attribute
>>
>> # file: tmp/sparse.txt
>> user.DOSATTRIB=0x000004000400000051000000200200000000000000000000209542d3b373dd01
>> 0x51 = 0x1 | 0x10 | 0x40 -----^^ | unrequested --^^^^^^^^^^^^^^^^
>> (ATTRIB | CREATE_TIME | ITIME) | creation time = btime
>> SPARSE --^
>> CIFS btime (/mnt/sparse.txt): 2026-11-13 21:13:27.167926400 +0000
>> [...]
>> create_time: Fri Nov 13 21:13:27 2026 UTC
>> [...]
>> CIFS btime (/mnt/sparse.txt): 2026-11-13 21:13:27.167926400 +0000
>>
>> test with setmode:
>>
>> echo data > /tmp/attrib.txt
>> chmod 777 /tmp/attrib.txt
>>
>> stat -c 'Local btime (%n): %w' /tmp/attrib.txt
>> getfattr -n user.DOSATTRIB -e hex /tmp/attrib.txt
>>
>> # modify attribute via CIFS
>> smbclient //127.0.0.1/test -U user%pass -c 'setmode attrib.txt +r'
>> getfattr -n user.DOSATTRIB -e hex /tmp/attrib.txt
>>
>> stat -c 'CIFS btime (%n): %w' /mnt/attrib.txt
>> smbclient //127.0.0.1/test -U user%pass -c 'allinfo attrib.txt'
>>
>> # evict cache so btime is read fresh again
>> umount /mnt
>> mount -t cifs //127.0.0.1/test /mnt -o username=user,password=pass
>> stat -c 'CIFS btime (%n): %w' /mnt/attrib.txt
>>
>> which prints:
>>
>> Local btime (/tmp/attrib.txt): 2026-11-13 21:13:27.195647069 +0000
>> /tmp/attrib.txt: user.DOSATTRIB: No such attribute
>>
>> # file: tmp/attrib.txt
>> user.DOSATTRIB=0x000004000400000051000000210000000000000000000000f6cf46d3b373dd01
>> 0x51 = 0x1 | 0x10 | 0x40 -----^^ | unrequested --^^^^^^^^^^^^^^^^
>> (ATTRIB | CREATE_TIME | ITIME) | creation time = btime
>> READONLY --^
>> CIFS btime (/mnt/attrib.txt): 2026-11-13 21:13:27.195647000 +0000
>> [...]
>> create_time: Fri Nov 13 21:13:27 2026 UTC
>> [...]
>> CIFS btime (/mnt/attrib.txt): 2026-11-13 21:13:27.195647000 +0000
>>
>> After this patch, the outputs should be:
>>
>> sparse:
>>
>> Local btime (/tmp/sparse.txt): 2026-11-13 21:20:25.856425751 +0000
>> /tmp/sparse.txt: user.DOSATTRIB: No such attribute
>> # file: tmp/sparse.txt
>> user.DOSATTRIB=0x0000040004000000010000002002000000000000000000000000000000000000
>> 0x01 = 0x1 (ATTRIB) -----^^ | no creation time --^^^^^^^^^^^^^^^^
>> SPARSE --^
>> CIFS btime (/mnt/sparse.txt): 2026-11-13 21:20:25.856425700 +0000
>> create_time: Fri Nov 13 21:20:26 2026 UTC
>> CIFS btime (/mnt/sparse.txt): 2026-11-13 21:20:25.856425700 +0000
>>
>> setmode:
>>
>> Local btime (/tmp/attrib.txt): 2026-11-13 21:20:25.976415893 +0000
>> /tmp/attrib.txt: user.DOSATTRIB: No such attribute
>> # file: tmp/attrib.txt
>> user.DOSATTRIB=0x0000040004000000010000002100000000000000000000000000000000000000
>> 0x01 = 0x1 (ATTRIB) -----^^ | no creation time --^^^^^^^^^^^^^^^^
>> READONLY --^
>> CIFS btime (/mnt/attrib.txt): 2026-11-13 21:20:25.976415800 +0000
>> create_time: Fri Nov 13 21:20:26 2026 UTC
>> CIFS btime (/mnt/attrib.txt): 2026-11-13 21:20:25.976415800 +0000
>>
>> Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") # ndr decode/basic info
>> Fixes: f44158485826 ("cifsd: add file operations") # ksmbd_vfs_fill_dentry_attrs
>> Fixes: 159e727f763d ("ksmbd: persist FSCTL_SET_SPARSE state") # sparse
>> Fixes: 0fb327626ad9 ("ksmbd: support file compression attributes") # compression
>> Cc: stable@vger.kernel.org
>> Assisted-by: Gemini:3.8-flash-high antigravity-cli-1.5.3
>> Signed-off-by: koraynilay <koray.fra@gmail.com>
> Can you check Sashiko's review comments ?
>
> https://sashiko.dev/#/patchset/20261113221610.392113-1-koray.fra%40gmail.com
Yes thanks, I am able to reproduce what sashiko said, I'll send a v2.
Best,
koraynilay
>
> Thanks.
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prev parent reply other threads:[~2026-11-14 0:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-13 22:16 [PATCH] ksmbd: decode and honor DOS attribute validity flags koraynilay
2026-11-14 0:26 ` Namjae Jeon
2026-11-14 0:58 ` koraynilay [this message]
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