Commit 394d70b8 authored by Yuto Ohnuki's avatar Yuto Ohnuki Committed by Carlos Maiolino
Browse files

xfs: save ailp before dropping the AIL lock in push callbacks 



In xfs_inode_item_push() and xfs_qm_dquot_logitem_push(), the AIL lock
is dropped to perform buffer IO. Once the cluster buffer no longer
protects the log item from reclaim, the log item may be freed by
background reclaim or the dquot shrinker. The subsequent spin_lock()
call dereferences lip->li_ailp, which is a use-after-free.

Fix this by saving the ailp pointer in a local variable while the AIL
lock is held and the log item is guaranteed to be valid.

Reported-by: default avatar <syzbot+652af2b3c5569c4ab63c@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=652af2b3c5569c4ab63c


Fixes: 90c60e16 ("xfs: xfs_iflush() is no longer necessary")
Cc: stable@vger.kernel.org # v5.9
Reviewed-by: default avatarDarrick J. Wong <djwong@kernel.org>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
Signed-off-by: default avatarYuto Ohnuki <ytohnuki@amazon.com>
Signed-off-by: default avatarCarlos Maiolino <cem@kernel.org>
parent 79ef34ec

fs/xfs/xfs_dquot_item.c

+7 −2
Original line number Diff line number Diff line
@@ -125,6 +125,7 @@ xfs_qm_dquot_logitem_push( 
	struct xfs_dq_logitem	*qlip = DQUOT_ITEM(lip);

	struct xfs_dquot	*dqp = qlip->qli_dquot;

	struct xfs_buf		*bp;

	struct xfs_ail		*ailp = lip->li_ailp;

	uint			rval = XFS_ITEM_SUCCESS;

	int			error;
@@ -153,7 +154,7 @@ xfs_qm_dquot_logitem_push( 
		goto out_unlock;

	}



	spin_unlock(&lip->li_ailp->ail_lock);

	spin_unlock(&ailp->ail_lock);



	error = xfs_dquot_use_attached_buf(dqp, &bp);

	if (error == -EAGAIN) {
@@ -172,9 +173,13 @@ xfs_qm_dquot_logitem_push( 
			rval = XFS_ITEM_FLUSHING;

	}

	xfs_buf_relse(bp);

	/*

	 * The buffer no longer protects the log item from reclaim, so

	 * do not reference lip after this point.

	 */



out_relock_ail:

	spin_lock(&lip->li_ailp->ail_lock);

	spin_lock(&ailp->ail_lock);

out_unlock:

	mutex_unlock(&dqp->q_qlock);

	return rval;

fs/xfs/xfs_inode_item.c

+7 −2
Original line number Diff line number Diff line
@@ -746,6 +746,7 @@ xfs_inode_item_push( 
	struct xfs_inode_log_item *iip = INODE_ITEM(lip);

	struct xfs_inode	*ip = iip->ili_inode;

	struct xfs_buf		*bp = lip->li_buf;

	struct xfs_ail		*ailp = lip->li_ailp;

	uint			rval = XFS_ITEM_SUCCESS;

	int			error;
@@ -771,7 +772,7 @@ xfs_inode_item_push( 
	if (!xfs_buf_trylock(bp))

		return XFS_ITEM_LOCKED;



	spin_unlock(&lip->li_ailp->ail_lock);

	spin_unlock(&ailp->ail_lock);



	/*

	 * We need to hold a reference for flushing the cluster buffer as it may
@@ -795,7 +796,11 @@ xfs_inode_item_push( 
		rval = XFS_ITEM_LOCKED;

	}



	spin_lock(&lip->li_ailp->ail_lock);

	/*

	 * The buffer no longer protects the log item from reclaim, so

	 * do not reference lip after this point.

	 */

	spin_lock(&ailp->ail_lock);

	return rval;

}