ksmbd: fix translation in acl entries

The ksmbd server performs translation of posix acls to smb acls.
Currently the translation is wrong since the idmapping of the mount is
used to map the ids into raw userspace ids but what is relevant is the
user namespace of ksmbd itself. The user namespace of ksmbd itself which
is the initial user namespace. The operation is similar to asking "What
*ids would a userspace process see given that k*id in the relevant user
namespace?". Before the final translation we need to apply the idmapping
of the mount in case any is used. Add two simple helpers for ksmbd.

Cc: Steve French <stfrench@microsoft.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Hyunchul Lee <hyc.lee@gmail.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/smbacl.c

@@ -587,14 +587,14 @@ static void set_posix_acl_entries_dacl(struct user_namespace *user_ns,
 			uid_t uid;
 			unsigned int sid_type = SIDOWNER;
 
-			uid = from_kuid(user_ns, pace->e_uid);
+			uid = posix_acl_uid_translate(user_ns, pace);
 			if (!uid)
 				sid_type = SIDUNIX_USER;
 			id_to_sid(uid, sid_type, sid);
 		} else if (pace->e_tag == ACL_GROUP) {
 			gid_t gid;
 
-			gid = from_kgid(user_ns, pace->e_gid);
+			gid = posix_acl_gid_translate(user_ns, pace);
 			id_to_sid(gid, SIDUNIX_GROUP, sid);
 		} else if (pace->e_tag == ACL_OTHER && !nt_aces_num) {
 			smb_copy_sid(sid, &sid_everyone);
@@ -653,12 +653,12 @@ posix_default_acl:
 		if (pace->e_tag == ACL_USER) {
 			uid_t uid;
 
-			uid = from_kuid(user_ns, pace->e_uid);
+			uid = posix_acl_uid_translate(user_ns, pace);
 			id_to_sid(uid, SIDCREATOR_OWNER, sid);
 		} else if (pace->e_tag == ACL_GROUP) {
 			gid_t gid;
 
-			gid = from_kgid(user_ns, pace->e_gid);
+			gid = posix_acl_gid_translate(user_ns, pace);
 			id_to_sid(gid, SIDCREATOR_GROUP, sid);
 		} else {
 			kfree(sid);
@@ -1234,11 +1234,9 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, struct path *path,
 			pa_entry = posix_acls->a_entries;
 			for (i = 0; i < posix_acls->a_count; i++, pa_entry++) {
 				if (pa_entry->e_tag == ACL_USER)
-					id = from_kuid(user_ns,
-						       pa_entry->e_uid);
+					id = posix_acl_uid_translate(user_ns, pa_entry);
 				else if (pa_entry->e_tag == ACL_GROUP)
-					id = from_kgid(user_ns,
-						       pa_entry->e_gid);
+					id = posix_acl_gid_translate(user_ns, pa_entry);
 				else
 					continue;
 

fs/ksmbd/smbacl.h

@@ -209,4 +209,29 @@ int set_info_sec(struct ksmbd_conn *conn, struct ksmbd_tree_connect *tcon,
 		 bool type_check);
 void id_to_sid(unsigned int cid, uint sidtype, struct smb_sid *ssid);
 void ksmbd_init_domain(u32 *sub_auth);
+
+static inline uid_t posix_acl_uid_translate(struct user_namespace *mnt_userns,
+					    struct posix_acl_entry *pace)
+{
+	kuid_t kuid;
+
+	/* If this is an idmapped mount, apply the idmapping. */
+	kuid = kuid_into_mnt(mnt_userns, pace->e_uid);
+
+	/* Translate the kuid into a userspace id ksmbd would see. */
+	return from_kuid(&init_user_ns, kuid);
+}
+
+static inline gid_t posix_acl_gid_translate(struct user_namespace *mnt_userns,
+					    struct posix_acl_entry *pace)
+{
+	kgid_t kgid;
+
+	/* If this is an idmapped mount, apply the idmapping. */
+	kgid = kgid_into_mnt(mnt_userns, pace->e_gid);
+
+	/* Translate the kgid into a userspace id ksmbd would see. */
+	return from_kgid(&init_user_ns, kgid);
+}
+
 #endif /* _SMBACL_H */

fs/ksmbd/vfs.c

@@ -1390,14 +1390,14 @@ static struct xattr_smb_acl *ksmbd_vfs_make_xattr_posix_acl(struct user_namespac
 		switch (pa_entry->e_tag) {
 		case ACL_USER:
 			xa_entry->type = SMB_ACL_USER;
-			xa_entry->uid = from_kuid(user_ns, pa_entry->e_uid);
+			xa_entry->uid = posix_acl_uid_translate(user_ns, pa_entry);
 			break;
 		case ACL_USER_OBJ:
 			xa_entry->type = SMB_ACL_USER_OBJ;
 			break;
 		case ACL_GROUP:
 			xa_entry->type = SMB_ACL_GROUP;
-			xa_entry->gid = from_kgid(user_ns, pa_entry->e_gid);
+			xa_entry->gid = posix_acl_gid_translate(user_ns, pa_entry);
 			break;
 		case ACL_GROUP_OBJ:
 			xa_entry->type = SMB_ACL_GROUP_OBJ;