Commit 04a8d07f authored Nov 29, 2021 by J. Bruce Fields Committed by Greg Kroah-Hartman Dec 22, 2021

nfsd: fix use-after-free due to delegation race



commit 548ec0805c399c65ed66c6641be467f717833ab5 upstream.

A delegation break could arrive as soon as we've called vfs_setlease.  A
delegation break runs a callback which immediately (in
nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru.  If we
then exit nfs4_set_delegation without hashing the delegation, it will be
freed as soon as the callback is done with it, without ever being
removed from del_recall_lru.

Symptoms show up later as use-after-free or list corruption warnings,
usually in the laundromat thread.

I suspect aba2072f4523 "nfsd: grant read delegations to clients holding
writes" made this bug easier to hit, but I looked as far back as v3.0
and it looks to me it already had the same problem.  So I'm not sure
where the bug was introduced; it may have been there from the beginning.

Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[Salvatore Bonaccorso: Backport for context changes to versions which do
not have 20b7d86f29d3 ("nfsd: use boottime for lease expiry calculation")]
Signed-off-by: Salvatore Bonaccorso <carnil@debian.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent a48f6a2b

fs/nfsd/nfs4state.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -844,6 +844,11 @@ hash_delegation_locked(struct nfs4_delegation dp, struct nfs4_file fp)
		return 0;
		}

		static bool delegation_hashed(struct nfs4_delegation *dp)
		{
		return !(list_empty(&dp->dl_perfile));
		}

		static bool
		unhash_delegation_locked(struct nfs4_delegation *dp)
		{
		@@ -851,7 +856,7 @@ unhash_delegation_locked(struct nfs4_delegation *dp)

		lockdep_assert_held(&state_lock);

		if (list_empty(&dp->dl_perfile))
		if (!delegation_hashed(dp))
		return false;

		dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
		@@ -3656,7 +3661,7 @@ static void nfsd4_cb_recall_prepare(struct nfsd4_callback *cb)
		* queued for a lease break. Don't queue it again.
		*/
		spin_lock(&state_lock);
		if (dp->dl_time == 0) {
		if (delegation_hashed(dp) && dp->dl_time == 0) {
		dp->dl_time = get_seconds();
		list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
		}