[PATCH] xfs_repair: fix bad next_unlinked field

[Eric Sandeen <sandeen@redhat.com>]

As of xfsprogs-4.17 we started testing whether the di_next_unlinked field
on an inode is valid in the inode verifiers. However, this field is never
tested or repaired during inode processing.

So if, for example, we had a completely zeroed-out inode, we'd detect and
fix the broken magic and version, but the invalid di_next_unlinked field
would not be touched, fail the write verifier, and prevent the inode from
being properly repaired or even written out.

Fix this by checking the di_next_unlinked inode field for validity and
clearing it if it is invalid.

Reported-by: John Jore <john@jore.no>
Fixes: 2949b4677 ("xfs: don't accept inode buffers with suspicious unlinked chains")
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

diff --git a/repair/dinode.c b/repair/dinode.c
index 8af2cb25..c5d2f350 100644
--- a/repair/dinode.c
+++ b/repair/dinode.c
@@ -2272,6 +2272,7 @@ process_dinode_int(xfs_mount_t *mp,
 	const int		is_free = 0;
 	const int		is_used = 1;
 	blkmap_t		*dblkmap = NULL;
+	xfs_agino_t		unlinked_ino;
 
 	*dirty = *isa_dir = 0;
 	*used = is_used;
@@ -2351,6 +2352,23 @@ process_dinode_int(xfs_mount_t *mp,
 		}
 	}
 
+	unlinked_ino = be32_to_cpu(dino->di_next_unlinked);
+	if (!xfs_verify_agino_or_null(mp, agno, unlinked_ino)) {
+		retval = 1;
+		if (!uncertain)
+			do_warn(_("bad next_unlinked 0x%x on inode %" PRIu64 "%c"),
+				(__s32)dino->di_next_unlinked, lino,
+				verify_mode ? '\n' : ',');
+		if (!verify_mode) {
+			if (!no_modify) {
+				do_warn(_(" resetting next_unlinked\n"));
+				clear_dinode_unlinked(mp, dino);
+				*dirty = 1;
+			} else
+				do_warn(_(" would reset next_unlinked\n"));
+		}
+	}
+
 	/*
 	 * We don't bother checking the CRC here - we cannot guarantee that when
 	 * we are called here that the inode has not already been modified in