[RFC PATCH v2 17/41] quota: don't account UUID and GUID owners

[Jan Koester]

Quota files and the quotactl interface use 32 bit ids. dqget() would
hash and store a UUID or GUID owner as -1, so all of them would share
one dquot, written out as id 4294967295.

Treat such ids like quota being off for them: dqget() returns -ESRCH,
which its callers already handle by not charging the inode. An inode
given to such an owner stays charged to the previous one.

Assisted-by: Claude:claude-opus-5-5

Signed-off-by: Jan Koester <jan.koester at tuxist.de>
---
 fs/quota/dquot.c      |  3 +++
 include/linux/quota.h | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 1c78c695d0..62f333f824 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -954,6 +954,9 @@ struct dquot *dqget(struct super_block *sb, struct kqid qid)
 
 	if (!qid_has_mapping(sb->s_user_ns, qid))
 		return ERR_PTR(-EINVAL);
+	/* Quota files hold 32 bit ids: like quota off for UUIDs and GUIDs */
+	if (!qid_is_legacy(qid))
+		return ERR_PTR(-ESRCH);
 
         if (!sb_has_quota_active(sb, qid.type))
 		return ERR_PTR(-ESRCH);
diff --git a/include/linux/quota.h b/include/linux/quota.h
index 89a0d83dda..00685209fd 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -80,6 +80,24 @@ extern qid_t from_kqid(struct user_namespace *to, struct kqid qid);
 extern qid_t from_kqid_munged(struct user_namespace *to, struct kqid qid);
 extern bool qid_valid(struct kqid qid);
 
+/**
+ *	qid_is_legacy - Report if a kqid fits the 32 bit ids of quota files
+ *	@qid: The kernel internal quota identifier to test.
+ *
+ *	UUID and GUID owners don't, and are not subject to quotas.
+ */
+static inline bool qid_is_legacy(struct kqid qid)
+{
+	switch (qid.type) {
+	case USRQUOTA:
+		return uid_is_legacy(qid.uid);
+	case GRPQUOTA:
+		return gid_is_legacy(qid.gid);
+	default:
+		return true;
+	}
+}
+
 /**
  *	make_kqid - Map a user-namespace, type, qid tuple into a kqid.
  *	@from: User namespace that the qid is in
-- 
2.56.0