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/fs/quota/dquot.c b/fs/quota/dquot.c
index ff21980..74706b6 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -841,6 +841,9 @@
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: