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Commit 044c9b67 authored by Jan Kara's avatar Jan Kara
Browse files

quota: Fix possible races during quota loading 



When loading new quota structure from disk, there is a possibility caller
of dqget() will see uninitialized data due to CPU reordering loads or
stores - loads from dquot can be reordered before test of DQ_ACTIVE_B
bit or setting of this bit could be reordered before filling of the
structure. Fix the issue by adding proper memory barriers.

Signed-off-by: default avatarJan Kara <jack@suse.cz>
parent 5a9530e4

fs/quota/dquot.c

+12 −0
Original line number Diff line number Diff line
@@ -411,6 +411,8 @@ int dquot_acquire(struct dquot *dquot) 
		ret = dqopt->ops[dquot->dq_id.type]->read_dqblk(dquot);

	if (ret < 0)

		goto out_iolock;

	/* Make sure flags update is visible after dquot has been filled */

	smp_mb__before_atomic();

	set_bit(DQ_READ_B, &dquot->dq_flags);

	/* Instantiate dquot if needed */

	if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags) && !dquot->dq_off) {
@@ -427,6 +429,11 @@ int dquot_acquire(struct dquot *dquot) 
			goto out_iolock;

		}

	}

	/*

	 * Make sure flags update is visible after on-disk struct has been

	 * allocated. Paired with smp_rmb() in dqget().

	 */

	smp_mb__before_atomic();

	set_bit(DQ_ACTIVE_B, &dquot->dq_flags);

out_iolock:

	mutex_unlock(&dqopt->dqio_mutex);
@@ -887,6 +894,11 @@ struct dquot *dqget(struct super_block *sb, struct kqid qid) 
			goto out;

		}

	}

	/*

	 * Make sure following reads see filled structure - paired with

	 * smp_mb__before_atomic() in dquot_acquire().

	 */

	smp_rmb();

#ifdef CONFIG_QUOTA_DEBUG

	BUG_ON(!dquot->dq_sb);	/* Has somebody invalidated entry under us? */

#endif