[PATCH] ksmbd: fix timestamp corruption on special values

[PATCH] ksmbd: fix timestamp corruption on special values

[koraynilay]

When a timestamp is being sent with "-1" or "-2" as its value because it
should be ignored, as specified in MS-FSCC 2.4.7 FileBasicInformation,
ksmbd would clobber it in both the xattr and on-disk value by setting it
to -1.

simple reproducer:

echo test > file.txt
smbclient //127.0.0.1/test -U user%pass -c "put file.txt repro.txt"
smbclient //127.0.0.1/test -U user%pass -c "allinfo repro.txt"
smbclient //127.0.0.1/test -U user%pass -c "setmode repro.txt +h"
stat repro.txt # the actual file on disk behind smb
smbclient //127.0.0.1/test -U user%pass -c "allinfo repro.txt"

which would show, respectively:

altname: REPRO~MQ.TXT
create_time:    Wed Nov 11 21:23:16 2026 UTC
access_time:    Wed Nov 11 21:23:16 2026 UTC
write_time:     Wed Nov 11 21:23:16 2026 UTC
change_time:    Wed Nov 11 21:23:16 2026 UTC
attributes: A (20)

  File: /tmp/repro.txt
[...]
Access: 1601-01-01 00:00:00.000000000 +0000
Modify: 2026-11-11 21:58:10.145349236 +0000
Change: 2026-11-11 21:58:10.206350216 +0000
 Birth: 2026-11-11 21:58:10.144349220 +0000

altname: REPRO~MQ.TXT
create_time:    Wed Dec 31 23:59:59 1969 UTC
access_time:    Mon Jan  1 00:00:04 1601 UTC
write_time:     Wed Nov 11 21:23:16 2026 UTC
change_time:    Wed Nov 11 21:23:16 2026 UTC
attributes: HA (22)

This patch also makes the smb2.timestamps.freeze-thaw test from
smbtorture pass.

Cc: stable@vger.kernel.org
Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Link: https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/16023025-8a78-492f-8b96-c873b042ac50
Assisted-by: Gemini:3.8-flash-high antigravity-cli-1.5.3
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
Another small-ish fix I found while implementing ptime[1].
(And probably won't be the last one :c)

Thanks.

[1]: https://lore.kernel.org/all/20261101015551.786044-1-koray.fra@gmail.com/T/#t

 fs/smb/server/smb2pdu.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 92843d2944e4..5b046f10e2ce 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -8867,6 +8867,7 @@ static int set_file_basic_info(struct ksmbd_file *fp,
 	const struct mnt_idmap *idmap;
 	__le32 attrs_mask = FILE_ATTRIBUTE_DIRECTORY_LE |
 		FILE_ATTRIBUTE_COMPRESSED_LE;
+	s64 crtime, time;
 	int rc = 0;
 
 	if (!(fp->daccess & FILE_WRITE_ATTRIBUTES_LE))
@@ -8882,21 +8883,25 @@ static int set_file_basic_info(struct ksmbd_file *fp,
 	    (file_info->Attributes & FILE_ATTRIBUTE_TEMPORARY_LE))
 		return -EINVAL;
 
-	if (file_info->CreationTime)
-		fp->create_time = le64_to_cpu(file_info->CreationTime);
+	crtime = (s64)le64_to_cpu(file_info->CreationTime);
+	if (crtime > 0)
+		fp->create_time = crtime;
 
-	if (file_info->LastAccessTime) {
+	time = (s64)le64_to_cpu(file_info->LastAccessTime);
+	if (time > 0) {
 		attrs.ia_atime = ksmbd_NTtimeToUnix(file_info->LastAccessTime);
 		attrs.ia_valid |= (ATTR_ATIME | ATTR_ATIME_SET);
 	}
 
-	if (file_info->ChangeTime) {
-		fp->change_time = le64_to_cpu(file_info->ChangeTime);
+	time = (s64)le64_to_cpu(file_info->ChangeTime);
+	if (time > 0) {
+		fp->change_time = time;
 		inode_set_ctime_to_ts(inode,
 				ksmbd_NTtimeToUnix(file_info->ChangeTime));
 	}
 
-	if (file_info->LastWriteTime) {
+	time = (s64)le64_to_cpu(file_info->LastWriteTime);
+	if (time > 0) {
 		attrs.ia_mtime = ksmbd_NTtimeToUnix(file_info->LastWriteTime);
 		attrs.ia_valid |= (ATTR_MTIME | ATTR_MTIME_SET | ATTR_CTIME);
 	}
@@ -8915,7 +8920,7 @@ static int set_file_basic_info(struct ksmbd_file *fp,
 	}
 
 	if (test_share_config_flag(share, KSMBD_SHARE_FLAG_STORE_DOS_ATTRS) &&
-	    (file_info->CreationTime || file_info->Attributes)) {
+	    (crtime > 0 || file_info->Attributes)) {
 		struct xattr_dos_attrib da = {0};
 
 		da.version = 4;

base-commit: ffde0bdfc69a0f01a081d9c1a213e63d5719e625
-- 
2.56.0

Re: [PATCH] ksmbd: fix timestamp corruption on special values

[Ian Bridges]

Hi,

On Wed, Nov 11, 2026 at 11:25:34PM +0100, koraynilay wrote:
> When a timestamp is being sent with "-1" or "-2" as its value because it
> should be ignored, as specified in MS-FSCC 2.4.7 FileBasicInformation,
> ksmbd would clobber it in both the xattr and on-disk value by setting it
> to -1.

I tested this with the ksmbd code from ksmbd-for-next. Before the
patch, setting any of the four times to -1 or -2 stored that value.
The access and write times on disk moved to 1901, and the creation
time in the DOS attribute xattr was overwritten. With the patch, -1
and -2 leave every time unchanged, and valid times are still set as
before. smbtorture confirms the result in the commit message, the rest
of its results are unchanged, and KASAN reports nothing.

Reviewed-by: Ian Bridges <icb@fastmail.org>
Tested-by: Ian Bridges <icb@fastmail.org>