4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Sandeen <redacted>

commit 93e8befc17f6d6ea92b0aee3741ceac8bca4590f upstream.

Jason reported that a corrupted filesystem failed to replay
the log with a metadata block out of bounds warning:

XFS (dm-2): _xfs_buf_find: Block out of range: block 0x80270fff8, EOFS 0x9c40000

_xfs_buf_find() and xfs_btree_get_bufs() return NULL if
that happens, and then when xfs_alloc_fix_freelist() calls
xfs_trans_binval() on that NULL bp, we oops with:

BUG: unable to handle kernel NULL pointer dereference at 00000000000000f8

We don't handle _xfs_buf_find errors very well, every
caller higher up the stack gets to guess at why it failed.
But we should at least handle it somehow, so return
EFSCORRUPTED here.

Reported-by: Jason L Tibbitts III <redacted>
Signed-off-by: Eric Sandeen <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <redacted>
Signed-off-by: Darrick J. Wong <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/xfs/libxfs/xfs_alloc.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c

@@ -1584,6 +1584,10 @@ xfs_alloc_ag_vextent_small(
 
 				bp = xfs_btree_get_bufs(args->mp, args->tp,
 					args->agno, fbno, 0);
+				if (!bp) {
+					error = -EFSCORRUPTED;
+					goto error0;
+				}
 				xfs_trans_binval(args->tp, bp);
 			}
 			args->len = 1;

@@ -2141,6 +2145,10 @@ xfs_alloc_fix_freelist(
 		if (error)
 			goto out_agbp_relse;
 		bp = xfs_btree_get_bufs(mp, tp, args->agno, bno, 0);
+		if (!bp) {
+			error = -EFSCORRUPTED;
+			goto out_agbp_relse;
+		}
 		xfs_trans_binval(tp, bp);
 	}