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quota: Ensure qids map to the filesystem

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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>
This commit is contained in:
Eric W. Biederman
2016-06-30 16:31:01 -05:00
parent 036d523641
commit d49d37624a
3 changed files with 19 additions and 6 deletions
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10
include/linux/quota.h
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@@ -179,6 +179,16 @@ 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;