Revert "(namespace) quota: Ensure qids map to the filesystem"

BugLink: https://bugs.launchpad.net/bugs/1644165

This reverts commit ec41f5ac.

The kernel fix for bug #1634964 breaks LXD userspace, in particular the
following commits:

ac7f3f73 (namespace) vfs: Don't modify inodes with a uid or gid unknown to the vfs
ca52383a (namespace) vfs: Don't create inodes with a uid or gid unknown to the vfs

LXD 2.0.6 will include changes to support these kernel changes, but it isn't
available yet on xenial, so for now we just revert these commits.
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

fs/quota/dquot.c

@@ -834,9 +834,6 @@ struct dquot *dqget(struct super_block *sb, struct kqid qid)
 	unsigned int hashent = hashfn(sb, qid);
 	struct dquot *dquot, *empty = NULL;
 
-	if (!qid_has_mapping(sb->s_user_ns, qid))
-		return ERR_PTR(-EINVAL);
-
         if (!sb_has_quota_active(sb, qid.type))
 		return ERR_PTR(-ESRCH);
 we_slept:

fs/quota/quota.c

@@ -211,7 +211,7 @@ static int quota_getquota(struct super_block *sb, int type, qid_t id,
 	if (!sb->s_qcop->get_dqblk)
 		return -ENOSYS;
 	qid = make_kqid(current_user_ns(), type, id);
-	if (!qid_has_mapping(sb->s_user_ns, qid))
+	if (!qid_valid(qid))
 		return -EINVAL;
 	ret = sb->s_qcop->get_dqblk(sb, qid, &fdq);
 	if (ret)
@@ -260,7 +260,7 @@ static int quota_setquota(struct super_block *sb, int type, qid_t id,
 	if (!sb->s_qcop->set_dqblk)
 		return -ENOSYS;
 	qid = make_kqid(current_user_ns(), type, id);
-	if (!qid_has_mapping(sb->s_user_ns, qid))
+	if (!qid_valid(qid))
 		return -EINVAL;
 	copy_from_if_dqblk(&fdq, &idq);
 	return sb->s_qcop->set_dqblk(sb, qid, &fdq);
@@ -553,7 +553,7 @@ static int quota_setxquota(struct super_block *sb, int type, qid_t id,
 	if (!sb->s_qcop->set_dqblk)
 		return -ENOSYS;
 	qid = make_kqid(current_user_ns(), type, id);
-	if (!qid_has_mapping(sb->s_user_ns, qid))
+	if (!qid_valid(qid))
 		return -EINVAL;
 	/* Are we actually setting timer / warning limits for all users? */
 	if (from_kqid(&init_user_ns, qid) == 0 &&
@@ -614,7 +614,7 @@ static int quota_getxquota(struct super_block *sb, int type, qid_t id,
 	if (!sb->s_qcop->get_dqblk)
 		return -ENOSYS;
 	qid = make_kqid(current_user_ns(), type, id);
-	if (!qid_has_mapping(sb->s_user_ns, qid))
+	if (!qid_valid(qid))
 		return -EINVAL;
 	ret = sb->s_qcop->get_dqblk(sb, qid, &qdq);
 	if (ret)

include/linux/quota.h

@@ -179,16 +179,6 @@ static inline struct kqid make_kqid_projid(kprojid_t projid)
 	return kqid;
 }
 
-/**
- *	qid_has_mapping - Report if a qid maps into a user namespace.
- *	@ns:  The user namespace to see if a value maps into.
- *	@qid: The kernel internal quota identifier to test.
- */
-static inline bool qid_has_mapping(struct user_namespace *ns, struct kqid qid)
-{
-	return from_kqid(ns, qid) != (qid_t) -1;
-}
-
 
 extern spinlock_t dq_data_lock;