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[PATCH 01/13] libxfs: be more forgiving of a v4 secondary sb w/ junk in

To: xfs@xxxxxxxxxxx
Subject: [PATCH 01/13] libxfs: be more forgiving of a v4 secondary sb w/ junk in v5 fields
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 4 Mar 2014 19:51:45 +1100
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1393923117-9559-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1393923117-9559-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

[userspace port]

Today, if xfs_sb_read_verify encounters a v4 superblock
with junk past v4 fields which includes data in sb_crc,
it will be treated as a failing checksum and a significant

There are known prior bugs which leave junk at the end
of the V4 superblock; we don't need to actually fail the
verification in this case if other checks pan out ok.

So if this is a secondary superblock, and the primary
superblock doesn't indicate that this is a V5 filesystem,
don't treat this as an actual checksum failure.

We should probably check the garbage condition as
we do in xfs_repair, and possibly warn about it
or self-heal, but that's a different scope of work.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
 libxfs/xfs_sb.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/libxfs/xfs_sb.c b/libxfs/xfs_sb.c
index 48b1a97..16088a6 100644
--- a/libxfs/xfs_sb.c
+++ b/libxfs/xfs_sb.c
@@ -542,6 +542,11 @@ xfs_sb_verify(
  * single bit error could clear the feature bit and unused parts of the
  * superblock are supposed to be zero. Hence a non-null crc field indicates 
  * we've potentially lost a feature bit and we should check it anyway.
+ *
+ * However, past bugs (i.e. in growfs) left non-zeroed regions beyond the
+ * last field in V4 secondary superblocks.  So for secondary superblocks,
+ * we are more forgiving, and ignore CRC failures if the primary doesn't
+ * indicate that the fs version is V5.
 static void
@@ -562,8 +567,12 @@ xfs_sb_read_verify(
                if (!xfs_verify_cksum(bp->b_addr, be16_to_cpu(dsb->sb_sectsize),
                                      offsetof(struct xfs_sb, sb_crc))) {
-                       error = EFSCORRUPTED;
-                       goto out_error;
+                       /* Only fail bad secondaries on a known V5 filesystem */
+                       if (bp->b_bn != XFS_SB_DADDR &&
+                           xfs_sb_version_hascrc(&mp->m_sb)) {
+                               error = EFSCORRUPTED;
+                               goto out_error;
+                       }
        error = xfs_sb_verify(bp, true);

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