[RFC PATCH 5/6] ksmbd: show classic users as S-1-22-1-<uid> on every server

[RFC PATCH 5/6] ksmbd: show classic users as S-1-22-1-<uid> on every server

[Jan Koester]

A classic uid appeared in security descriptors as the server's own
domain SID + uid. That domain SID comes from user space and differs from
server to server (ksmbd-tools and sharedd derive it per machine), so
the same owner had a different SID on every file server, and the RID
looked like a domain account's.

Show them as S-1-22-1-<uid>, the SID ksmbd already used for root and
that S-1-22-2-<gid> pairs with for groups. Keep taking the old form when
a client sets it, and keep it in the session's SIDs, so descriptors
stored before still match.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Jan Koester <jan.koester@tuxist.de>
---
 fs/smb/server/smbacl.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c
index d6be65e3a9..769864d64e 100644
--- a/fs/smb/server/smbacl.c
+++ b/fs/smb/server/smbacl.c
@@ -300,14 +300,16 @@ static u32 sid_to_id_r(const struct smb_sid *psid, u8 *id)
 }
 
 /*
- * The SID ksmbd itself gives an id: a classic one the usual SIDs, a UUID
- * or GUID S-1-22-<kind>-w0-w1-w2-w3.
+ * The SID ksmbd itself gives an id: a classic uid S-1-22-1-<uid>, the same
+ * on every server (it used to be the server's own domain SID + uid), a
+ * classic gid S-1-22-2-<gid>, a UUID or GUID S-1-22-<kind>-w0-w1-w2-w3.
  */
 static void native_uid_sid(kuid_t uid, uint sidtype, struct smb_sid *ssid)
 {
-	if (uid_is_legacy(uid) || sidtype == SIDCREATOR_OWNER ||
-	    sidtype == SIDCREATOR_GROUP)
+	if (sidtype == SIDCREATOR_OWNER || sidtype == SIDCREATOR_GROUP)
 		id_to_sid(from_kuid_munged(&init_user_ns, uid), sidtype, ssid);
+	else if (uid_is_legacy(uid))
+		id_to_sid(from_kuid_munged(&init_user_ns, uid), SIDUNIX_USER, ssid);
 	else if (uid.type == KID_UUID)
 		id_r_to_sid(SID_UNIX_UUID_USER, uid.uuid.b, ssid);
 	else
@@ -373,13 +375,14 @@ static bool sid_equal(const struct smb_sid *a, const struct smb_sid *b)
 /*
  * The SIDs a user's ACL entries may name, like a Windows access token: the
  * user's and its groups', each the account's own SID (if user space maps
- * one) and ksmbd's. Built at login; a
+ * one) and ksmbd's -- for a classic uid also the server's domain SID + uid
+ * of older ksmbd, which stored descriptors may hold. Built at login; a
  * mapping user space couldn't give then is missing for the session (its
  * ACL entries don't match: access is denied, not granted).
  */
 void ksmbd_user_set_token(struct ksmbd_user *user)
 {
-	int i, n = 0, max = 2 + 2 * (user->ngroups + 1);
+	int i, n = 0, max = 3 + 2 * (user->ngroups + 1);
 	struct smb_sid *sids;
 
 	sids = kcalloc(max, sizeof(*sids), KSMBD_DEFAULT_GFP);
@@ -388,6 +391,9 @@ void ksmbd_user_set_token(struct ksmbd_user *user)
 	if (!mapped_uid_sid(user->kuid, &sids[n]))
 		n++;
 	native_uid_sid(user->kuid, SIDOWNER, &sids[n++]);
+	if (uid_is_legacy(user->kuid) && !uid_eq(user->kuid, GLOBAL_ROOT_UID))
+		id_to_sid(from_kuid_munged(&init_user_ns, user->kuid), SIDOWNER,
+			  &sids[n++]);
 	for (i = -1; i < user->ngroups; i++) {
 		kgid_t gid = i < 0 ? user->kgid : user->sgid[i];
 
@@ -519,8 +525,15 @@ static int sid_to_id(struct mnt_idmap *idmap,
 		kuid_t uid;
 		uid_t id;
 
-		/* Only the server domain RID has a local uid representation. */
-		sid_prefix = &server_conf.domain_sid;
+		/*
+		 * A local uid: S-1-22-1-<uid>, or the server's domain SID +
+		 * uid that ksmbd used to show (stored descriptors have it).
+		 */
+		if (psid->num_subauth == sid_unix_users.num_subauth + 1 &&
+		    !compare_sids(psid, &sid_unix_users))
+			sid_prefix = &sid_unix_users;
+		else
+			sid_prefix = &server_conf.domain_sid;
 		if (psid->num_subauth != sid_prefix->num_subauth + 1 ||
 		    compare_sids(psid, sid_prefix))
 			return -EINVAL;
-- 
2.56.0

Re: [RFC PATCH 5/6] ksmbd: show classic users as S-1-22-1-<uid> on every server

[Ian Bridges]

Hi Jan,

On Tue, Nov 10, 2026 at 09:02:52AM +0000, Jan Koester wrote:
> +	else if (uid_is_legacy(uid))
> +		id_to_sid(from_kuid_munged(&init_user_ns, uid), SIDUNIX_USER, ssid);

smb_check_perm_dacl() seems to still build the caller's own SID in the
old form. For a user other than root, would an ACE that a client writes
for S-1-22-1-<uid> then match the user only through the token? If
ksmbd_user_set_token() builds no token, as when its allocation fails in
4/6, would a deny ACE on the user in the new form stop applying? With a
deny for S-1-22-1-<uid> followed by an allow for Everyone, the user
would then get the access the deny should refuse.

Thanks,
Ian

[RFC PATCH 0/6] ksmbd: Windows SIDs for user and group ids

[Jan Koester]

Hi,

Windows names owners and ACL entries by SID; for a domain account that
is its objectSid. ksmbd shows a file's owner, group and POSIX ACL
entries as S-1-22 SIDs or as its server domain SID + uid, which a
Windows client can't relate to the domain's accounts, and a SID a client
sets for a domain account doesn't map back to an id at all. This series
lets user space, which knows the directory, translate between ids and
SIDs in both directions, for accounts that are logged in or not.

It applies on top of the UUID/GUID id RFC (uid_r v2,
<cover.1792552161.git.jan.koester@tuxist.de>) and the NTLM pass-through
series (<cover.1792345559.git.jan.koester@gmx.net>); the netlink events
it adds follow theirs. Patches 1-3 are independent of uid_r in substance;
I can rebase them onto mainline to go on their own if that is preferred.

1/6 ksmbd ignored the owner and group of a descriptor without a DACL,
    which is what Windows sends to take ownership (and smbcacls -C/-G),
    and still reported success.

2/6 After setting a POSIX ACL from a DACL, the following chmod used the
    owning group's bits as the mask and left named entries without
    effect.

3/6 passes the domain of an NTLM login (NTLMSSP DomainName) to user
    space in the formerly reserved room of the login request, so a user
    space serving several domains can tell DOMAIN\user from OTHER\user.

4/6 adds KSMBD_EVENT_SID_MAP_REQUEST/RESPONSE for a user space that sets
    KSMBD_GLOBAL_FLAG_SID_MAP at startup: the SID of an id ksmbd shows,
    the id of a domain SID a client sets. Answers are cached (mappings
    5 minutes, "none" 1 minute, "couldn't say" never). Showing a
    descriptor never fails on a missing mapping; setting one fails with
    STATUS_NO_LOGON_SERVERS, STATUS_INVALID_OWNER or
    STATUS_INVALID_PRIMARY_GROUP instead of being applied in part or
    ignored. The session user also matches ACEs for its groups' SIDs,
    like a Windows access token.

5/6 shows classic users as S-1-22-1-<uid> instead of the per-server
    domain SID + uid, and still takes the old form.

6/6 documents it in Documentation/userspace-api/uid_r.rst.

The user space side is sharedd (FenrirOS' ksmbd user space) with
adconnect for the directory lookups. Tested in a VM against a directory
server: owner and group of accounts that aren't logged in, ownership and
group changes, DACL round trips, a session getting access only through
a nested group, inherited CREATOR OWNER ACEs, and the directory going
away (cached mappings stay, new ones fail cleanly).

Questions:
- Is a netlink round trip per uncached id acceptable here, or would you
  rather have user space push the mappings of a session's ids at login
  only? The latter can't cover owners that aren't logged in.
- compare_sids() matches a SID against any prefix of it; the token uses
  an exact comparison. Should the existing callers move to that too?

Thanks,
Jan

Jan Koester (6):
  ksmbd: don't ignore the owner and group of a descriptor without a DACL
  ksmbd: keep named ACL entries effective when a DACL sets a POSIX ACL
  ksmbd: pass the domain of an NTLM login to user space
  ksmbd: map user and group ids to Windows SIDs through user space
  ksmbd: show classic users as S-1-22-1-<uid> on every server
  Documentation: uid_r: describe ksmbd's SID mapping

 Documentation/userspace-api/uid_r.rst |  18 +-
 fs/smb/server/Makefile                |   2 +-
 fs/smb/server/idmap.c                 | 320 ++++++++++++++++++++++++++
 fs/smb/server/idmap.h                 |  25 ++
 fs/smb/server/ksmbd_netlink.h         |  62 ++++-
 fs/smb/server/mgmt/user_config.c      |  21 +-
 fs/smb/server/mgmt/user_config.h      |   7 +-
 fs/smb/server/server.c                |   2 +
 fs/smb/server/smb2pdu.c               |  35 ++-
 fs/smb/server/smbacl.c                | 256 ++++++++++++++++++---
 fs/smb/server/smbacl.h                |  18 +-
 fs/smb/server/transport_ipc.c         |  72 +++++-
 fs/smb/server/transport_ipc.h         |   5 +-
 13 files changed, 793 insertions(+), 50 deletions(-)
 create mode 100644 fs/smb/server/idmap.c
 create mode 100644 fs/smb/server/idmap.h


base-commit: bdd1d550e3f518d445d199c8ee73dc962c5abab8
-- 
2.56.0

[RFC PATCH 5/6] ksmbd: show classic users as S-1-22-1-<uid> on every server

[Jan Koester]

A classic uid appeared in security descriptors as the server's own
domain SID + uid. That domain SID comes from user space and differs from
server to server (ksmbd-tools and sharedd derive it per machine), so
the same owner had a different SID on every file server, and the RID
looked like a domain account's.

Show them as S-1-22-1-<uid>, the SID ksmbd already used for root and
that S-1-22-2-<gid> pairs with for groups. Keep taking the old form when
a client sets it, and keep it in the session's SIDs, so descriptors
stored before still match.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Jan Koester <jan.koester@tuxist.de>
---
 fs/smb/server/smbacl.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c
index d6be65e3a9..769864d64e 100644
--- a/fs/smb/server/smbacl.c
+++ b/fs/smb/server/smbacl.c
@@ -300,14 +300,16 @@ static u32 sid_to_id_r(const struct smb_sid *psid, u8 *id)
 }
 
 /*
- * The SID ksmbd itself gives an id: a classic one the usual SIDs, a UUID
- * or GUID S-1-22-<kind>-w0-w1-w2-w3.
+ * The SID ksmbd itself gives an id: a classic uid S-1-22-1-<uid>, the same
+ * on every server (it used to be the server's own domain SID + uid), a
+ * classic gid S-1-22-2-<gid>, a UUID or GUID S-1-22-<kind>-w0-w1-w2-w3.
  */
 static void native_uid_sid(kuid_t uid, uint sidtype, struct smb_sid *ssid)
 {
-	if (uid_is_legacy(uid) || sidtype == SIDCREATOR_OWNER ||
-	    sidtype == SIDCREATOR_GROUP)
+	if (sidtype == SIDCREATOR_OWNER || sidtype == SIDCREATOR_GROUP)
 		id_to_sid(from_kuid_munged(&init_user_ns, uid), sidtype, ssid);
+	else if (uid_is_legacy(uid))
+		id_to_sid(from_kuid_munged(&init_user_ns, uid), SIDUNIX_USER, ssid);
 	else if (uid.type == KID_UUID)
 		id_r_to_sid(SID_UNIX_UUID_USER, uid.uuid.b, ssid);
 	else
@@ -373,13 +375,14 @@ static bool sid_equal(const struct smb_sid *a, const struct smb_sid *b)
 /*
  * The SIDs a user's ACL entries may name, like a Windows access token: the
  * user's and its groups', each the account's own SID (if user space maps
- * one) and ksmbd's. Built at login; a
+ * one) and ksmbd's -- for a classic uid also the server's domain SID + uid
+ * of older ksmbd, which stored descriptors may hold. Built at login; a
  * mapping user space couldn't give then is missing for the session (its
  * ACL entries don't match: access is denied, not granted).
  */
 void ksmbd_user_set_token(struct ksmbd_user *user)
 {
-	int i, n = 0, max = 2 + 2 * (user->ngroups + 1);
+	int i, n = 0, max = 3 + 2 * (user->ngroups + 1);
 	struct smb_sid *sids;
 
 	sids = kcalloc(max, sizeof(*sids), KSMBD_DEFAULT_GFP);
@@ -388,6 +391,9 @@ void ksmbd_user_set_token(struct ksmbd_user *user)
 	if (!mapped_uid_sid(user->kuid, &sids[n]))
 		n++;
 	native_uid_sid(user->kuid, SIDOWNER, &sids[n++]);
+	if (uid_is_legacy(user->kuid) && !uid_eq(user->kuid, GLOBAL_ROOT_UID))
+		id_to_sid(from_kuid_munged(&init_user_ns, user->kuid), SIDOWNER,
+			  &sids[n++]);
 	for (i = -1; i < user->ngroups; i++) {
 		kgid_t gid = i < 0 ? user->kgid : user->sgid[i];
 
@@ -519,8 +525,15 @@ static int sid_to_id(struct mnt_idmap *idmap,
 		kuid_t uid;
 		uid_t id;
 
-		/* Only the server domain RID has a local uid representation. */
-		sid_prefix = &server_conf.domain_sid;
+		/*
+		 * A local uid: S-1-22-1-<uid>, or the server's domain SID +
+		 * uid that ksmbd used to show (stored descriptors have it).
+		 */
+		if (psid->num_subauth == sid_unix_users.num_subauth + 1 &&
+		    !compare_sids(psid, &sid_unix_users))
+			sid_prefix = &sid_unix_users;
+		else
+			sid_prefix = &server_conf.domain_sid;
 		if (psid->num_subauth != sid_prefix->num_subauth + 1 ||
 		    compare_sids(psid, sid_prefix))
 			return -EINVAL;
-- 
2.56.0