[PATCH] repair: ensure that unused superblock fields are zeroed

From: Dave Chinner <dchinner@redhat.com>

When we grab a superblock off disk via get_sb(), we don't know what
the in-memory superblock we are filling out contained. We ned to
ensure that the entire structure is returned in an initialised
state regardless of which fields libxfs_sb_from_disk() populates
from disk. In this case, it doesn't populate the sb_crc field,
and so uninitialised values can escape through to disk on v4
filesystems because of this. This causes xfs/031 to fail on v4
filesystems.

Reported-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 repair/sb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/repair/sb.c b/repair/sb.c
index b111aca..d928dc0 100644
--- a/repair/sb.c
+++ b/repair/sb.c
@@ -518,6 +518,7 @@ get_sb(xfs_sb_t *sbp, xfs_off_t off, int size, xfs_agnumber_t agno)
 		exit(1);
 	}
 	memset(buf, 0, size);
+	memset(sbp, 0, sizeof(*sbp));
 
 	/* try and read it first */