xfs: handle error if xfs_btree_get_bufs fails

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 <tibbs@math.uh.edu>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 744dcae..f965ce8 100644 (file)
--- 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);
        }