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[PATCH] xfs: superblock buffers need to be sector sized

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: superblock buffers need to be sector sized
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 24 Feb 2015 18:12:24 +1100
Delivered-to: xfs@xxxxxxxxxxx
From: Dave Chinner <dchinner@xxxxxxxxxx>

In secondary_sb_wack() we zero the unused portion of both the
on-disk superblock and the in-memory copy that we have. When
the device sector size is 4k, this causes xfs_repair to crash like
so:

# xfs_repair /dev/ram1
Phase 1 - find and verify superblock...
Phase 2 - using internal log
        - zero log...
        - scan filesystem freespace and inode maps...
bad magic number
bad on-disk superblock 3 - bad magic number
primary/secondary superblock 3 conflict - AG superblock geometry info conflicts 
with filesystem geometry
zeroing unused portion of secondary superblock (AG #3)
#

The stack trace is indicative:

#0  memset ()
#1  0x000000000040404b in secondary_sb_wack
#2  verify_set_agheader
#3  0x0000000000427b4b in scan_ag
#4  0x000000000042a2ca in worker_thread
#5  0x00007ffff77ba0a4 in start_thread
#6  0x00007ffff74efc2d in clone

Which points at memset overrunning the in memory buffer, as it is
only 512 bytes in length.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 repair/scan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/repair/scan.c b/repair/scan.c
index ce8d7f5..12aa782 100644
--- a/repair/scan.c
+++ b/repair/scan.c
@@ -1485,7 +1485,7 @@ scan_ag(
        int             status;
        char            *objname = NULL;
 
-       sb = (struct xfs_sb *)calloc(BBSIZE, 1);
+       sb = (struct xfs_sb *)calloc(BBTOB(XFS_FSS_TO_BB(mp, 1)), 1);
        if (!sb) {
                do_error(_("can't allocate memory for superblock\n"));
                return;
-- 
2.0.0

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