quota: Ensure qids map to the filesystem
Introduce the helper qid_has_mapping and use it to ensure that the
quota system only considers qids that map to the filesystems
s_user_ns.
In practice for quota supporting filesystems today this is the exact
same check as qid_valid. As only 0xffffffff aka (qid_t)-1 does not
map into init_user_ns.
Replace the qid_valid calls with qid_has_mapping as values come in
from userspace. This is harmless today and it prepares the quota
system to work on filesystems with quotas but mounted by unprivileged
users.
Call qid_has_mapping from dqget. This ensures the passed in qid has a
prepresentation on the underlying filesystem. Previously this was
unnecessary as filesystesm never had qids that could not map. With
the introduction of filesystems outside of s_user_ns this will not
remain true.
All of this ensures the quota code never has to deal with qids that
don't map to the underlying filesystem.
Cc: Jan Kara <jack@suse.cz>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/include/linux/quota.h b/include/linux/quota.h
index 9dfb6bc..1db16ee 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -179,6 +179,16 @@
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;