From: Namjae Jeon <linkinjeon@kernel.org>
Date: Wed, 1 Jul 2026 13:58:35 +0000 (+0900)
Subject: ksmbd: validate SID namespace before mapping IDs
X-Git-Tag: v7.2-rc3~28^2~9
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=fbe0bb2b75eb3c61e8464486506253d1b471240b;p=thirdparty%2Fkernel%2Flinux.git

ksmbd: validate SID namespace before mapping IDs

sid_to_id() currently treats the last subauthority of any owner or group
SID as a Unix uid or gid. For example, this maps Everyone (S-1-1-0) to
uid 0 and BUILTIN\Users (S-1-5-32-545) to gid 545.

When an SMB2 CREATE security descriptor contains those SIDs, ksmbd
attempts to change the newly created file to the bogus Unix ownership.
notify_change() then returns -EPERM, which makes smb2.create.aclfile fail
with NT_STATUS_SHARING_VIOLATION.

Validate the SID prefix before extracting its RID. Only server-domain
owner SIDs and S-1-22-2 Unix group SIDs have local ID representations.
Treat other valid Windows SIDs as unmapped so their original values can
still be preserved in the NT ACL xattr.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---

diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c
index 9c59c8f73b66..67b39b4d218c 100644
--- a/fs/smb/server/smbacl.c
+++ b/fs/smb/server/smbacl.c
@@ -258,6 +258,7 @@ static int sid_to_id(struct mnt_idmap *idmap,
 		     struct smb_sid *psid, uint sidtype,
 		     struct smb_fattr *fattr)
 {
+	const struct smb_sid *sid_prefix;
 	int rc = -EINVAL;
 
 	/*
@@ -279,6 +280,12 @@ 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;
+		if (psid->num_subauth != sid_prefix->num_subauth + 1 ||
+		    compare_sids(psid, sid_prefix))
+			return -EINVAL;
+
 		id = le32_to_cpu(psid->sub_auth[psid->num_subauth - 1]);
 		uid = KUIDT_INIT(id);
 		uid = from_vfsuid(idmap, &init_user_ns, VFSUIDT_INIT(uid));
@@ -290,6 +297,12 @@ static int sid_to_id(struct mnt_idmap *idmap,
 		kgid_t gid;
 		gid_t id;
 
+		/* Local gids are represented by S-1-22-2-<gid>. */
+		sid_prefix = &sid_unix_groups;
+		if (psid->num_subauth != sid_prefix->num_subauth + 1 ||
+		    compare_sids(psid, sid_prefix))
+			return -EINVAL;
+
 		id = le32_to_cpu(psid->sub_auth[psid->num_subauth - 1]);
 		gid = KGIDT_INIT(id);
 		gid = from_vfsgid(idmap, &init_user_ns, VFSGIDT_INIT(gid));
@@ -900,9 +913,9 @@ int parse_sec_desc(struct mnt_idmap *idmap, struct smb_ntsd *pntsd,
 
 		rc = sid_to_id(idmap, owner_sid_ptr, SIDOWNER, fattr);
 		if (rc) {
-			pr_err("%s: Error %d mapping Owner SID to uid\n",
-			       __func__, rc);
+			ksmbd_debug(SMB, "Owner SID has no Unix uid mapping\n");
 			owner_sid_ptr = NULL;
+			rc = 0;
 		}
 	}
 
@@ -918,9 +931,9 @@ int parse_sec_desc(struct mnt_idmap *idmap, struct smb_ntsd *pntsd,
 		}
 		rc = sid_to_id(idmap, group_sid_ptr, SIDUNIX_GROUP, fattr);
 		if (rc) {
-			pr_err("%s: Error %d mapping Group SID to gid\n",
-			       __func__, rc);
+			ksmbd_debug(SMB, "Group SID has no Unix gid mapping\n");
 			group_sid_ptr = NULL;
+			rc = 0;
 		}
 	}