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quota: Fix possible races during quota loading

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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: Jan Kara <jack@suse.cz>
This commit is contained in:
Jan Kara 2016-02-18 13:20:20 +01:00
parent 5a9530e498
commit 044c9b6753
1 changed files with 12 additions and 0 deletions
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12
fs/quota/dquot.c
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@ -411,6 +411,8 @@ int dquot_acquire(struct dquot *dquot)
ret = dqopt->ops[dquot->dq_id.type]->read_dqblk(dquot); ret = dqopt->ops[dquot->dq_id.type]->read_dqblk(dquot);
if (ret < 0) if (ret < 0)
goto out_iolock; 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); set_bit(DQ_READ_B, &dquot->dq_flags);
/* Instantiate dquot if needed */ /* Instantiate dquot if needed */
if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags) && !dquot->dq_off) { 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; 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); set_bit(DQ_ACTIVE_B, &dquot->dq_flags);
out_iolock: out_iolock:
mutex_unlock(&dqopt->dqio_mutex); mutex_unlock(&dqopt->dqio_mutex);
@ -887,6 +894,11 @@ we_slept:
goto out; goto out;
} }
} }
/*
* Make sure following reads see filled structure - paired with
* smp_mb__before_atomic() in dquot_acquire().
*/
smp_rmb();
#ifdef CONFIG_QUOTA_DEBUG #ifdef CONFIG_QUOTA_DEBUG
BUG_ON(!dquot->dq_sb); /* Has somebody invalidated entry under us? */ BUG_ON(!dquot->dq_sb); /* Has somebody invalidated entry under us? */
#endif #endif