Changes since last update:

- Fix firstfsb variables that we left uninitialized, which could lead to
   locking problems.
 - Check for NULL metadata buffer pointers before using them.
 - Don't allow btree cursor manipulation if the btree block is corrupt.
   Better to just shut down.
 - Fix infinite loop problems in quotacheck.
 - Fix buffer overrun when validating directory blocks.
 - Fix deadlock problem in bunmapi.
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Merge tag 'xfs-4.13-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux

Pull xfs fixes from Darrick Wong:

 - fix firstfsb variables that we left uninitialized, which could lead
   to locking problems.

 - check for NULL metadata buffer pointers before using them.

 - don't allow btree cursor manipulation if the btree block is corrupt.
   Better to just shut down.

 - fix infinite loop problems in quotacheck.

 - fix buffer overrun when validating directory blocks.

 - fix deadlock problem in bunmapi.

* tag 'xfs-4.13-fixes-2' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux:
  xfs: fix multi-AG deadlock in xfs_bunmapi
  xfs: check that dir block entries don't off the end of the buffer
  xfs: fix quotacheck dquot id overflow infinite loop
  xfs: check _alloc_read_agf buffer pointer before using
  xfs: set firstfsb to NULLFSBLOCK before feeding it to _bmapi_write
  xfs: check _btree_check_block value

fs/xfs/libxfs/xfs_bmap.c

@@ -5435,6 +5435,7 @@ __xfs_bunmapi(
 	xfs_fsblock_t		sum;
 	xfs_filblks_t		len = *rlen;	/* length to unmap in file */
 	xfs_fileoff_t		max_len;
+	xfs_agnumber_t		prev_agno = NULLAGNUMBER, agno;
 
 	trace_xfs_bunmap(ip, bno, len, flags, _RET_IP_);
 
@@ -5534,6 +5535,17 @@ __xfs_bunmapi(
 		 */
 		del = got;
 		wasdel = isnullstartblock(del.br_startblock);
+
+		/*
+		 * Make sure we don't touch multiple AGF headers out of order
+		 * in a single transaction, as that could cause AB-BA deadlocks.
+		 */
+		if (!wasdel) {
+			agno = XFS_FSB_TO_AGNO(mp, del.br_startblock);
+			if (prev_agno != NULLAGNUMBER && prev_agno > agno)
+				break;
+			prev_agno = agno;
+		}
 		if (got.br_startoff < start) {
 			del.br_startoff = start;
 			del.br_blockcount -= start - got.br_startoff;
@@ -6499,6 +6511,15 @@ xfs_bmap_finish_one(
 	xfs_fsblock_t			firstfsb;
 	int				error = 0;
 
+	/*
+	 * firstfsb is tied to the transaction lifetime and is used to
+	 * ensure correct AG locking order and schedule work item
+	 * continuations.  XFS_BUI_MAX_FAST_EXTENTS (== 1) restricts us
+	 * to only making one bmap call per transaction, so it should
+	 * be safe to have it as a local variable here.
+	 */
+	firstfsb = NULLFSBLOCK;
+
 	trace_xfs_bmap_deferred(tp->t_mountp,
 			XFS_FSB_TO_AGNO(tp->t_mountp, startblock), type,
 			XFS_FSB_TO_AGBNO(tp->t_mountp, startblock),

fs/xfs/libxfs/xfs_btree.c

@@ -728,7 +728,8 @@ xfs_btree_firstrec(
 	 * Get the block pointer for this level.
 	 */
 	block = xfs_btree_get_block(cur, level, &bp);
-	xfs_btree_check_block(cur, block, level, bp);
+	if (xfs_btree_check_block(cur, block, level, bp))
+		return 0;
 	/*
 	 * It's empty, there is no such record.
 	 */
@@ -757,7 +758,8 @@ xfs_btree_lastrec(
 	 * Get the block pointer for this level.
 	 */
 	block = xfs_btree_get_block(cur, level, &bp);
-	xfs_btree_check_block(cur, block, level, bp);
+	if (xfs_btree_check_block(cur, block, level, bp))
+		return 0;
 	/*
 	 * It's empty, there is no such record.
 	 */

fs/xfs/libxfs/xfs_dir2_data.c

@@ -136,6 +136,8 @@ __xfs_dir3_data_check(
 		 */
 		if (be16_to_cpu(dup->freetag) == XFS_DIR2_DATA_FREE_TAG) {
 			XFS_WANT_CORRUPTED_RETURN(mp, lastfree == 0);
+			XFS_WANT_CORRUPTED_RETURN(mp, endp >=
+					p + be16_to_cpu(dup->length));
 			XFS_WANT_CORRUPTED_RETURN(mp,
 				be16_to_cpu(*xfs_dir2_data_unused_tag_p(dup)) ==
 					       (char *)dup - (char *)hdr);
@@ -164,6 +166,8 @@ __xfs_dir3_data_check(
 		XFS_WANT_CORRUPTED_RETURN(mp, dep->namelen != 0);
 		XFS_WANT_CORRUPTED_RETURN(mp,
 			!xfs_dir_ino_validate(mp, be64_to_cpu(dep->inumber)));
+		XFS_WANT_CORRUPTED_RETURN(mp, endp >=
+				p + ops->data_entsize(dep->namelen));
 		XFS_WANT_CORRUPTED_RETURN(mp,
 			be16_to_cpu(*ops->data_entry_tag_p(dep)) ==
 					       (char *)dep - (char *)hdr);

fs/xfs/libxfs/xfs_refcount.c

@@ -1638,6 +1638,10 @@ xfs_refcount_recover_cow_leftovers(
 	error = xfs_alloc_read_agf(mp, tp, agno, 0, &agbp);
 	if (error)
 		goto out_trans;
+	if (!agbp) {
+		error = -ENOMEM;
+		goto out_trans;
+	}
 	cur = xfs_refcountbt_init_cursor(mp, tp, agbp, agno, NULL);
 
 	/* Find all the leftover CoW staging extents. */

fs/xfs/xfs_qm.c

@@ -111,6 +111,9 @@ restart:
 			skipped = 0;
 			break;
 		}
+		/* we're done if id overflows back to zero */
+		if (!next_index)
+			break;
 	}
 
 	if (skipped) {

fs/xfs/xfs_reflink.c

@@ -170,6 +170,8 @@ xfs_reflink_find_shared(
 	error = xfs_alloc_read_agf(mp, tp, agno, 0, &agbp);
 	if (error)
 		return error;
+	if (!agbp)
+		return -ENOMEM;
 
 	cur = xfs_refcountbt_init_cursor(mp, tp, agbp, agno, NULL);
 
@@ -329,7 +331,7 @@ xfs_reflink_convert_cow_extent(
 	xfs_filblks_t			count_fsb,
 	struct xfs_defer_ops		*dfops)
 {
-	xfs_fsblock_t			first_block;
+	xfs_fsblock_t			first_block = NULLFSBLOCK;
 	int				nimaps = 1;
 
 	if (imap->br_state == XFS_EXT_NORM)