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From 35da59eaf201d5935d7047657355f129f3791d9a Mon Sep 17 00:00:00 2001
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From: "Darrick J. Wong" <darrick.wong@oracle.com>
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Date: Sat, 11 Jan 2014 13:54:57 -0500
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Subject: [PATCH 1/2] libext2fs: detect correct superblock adjustments when
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loading backup groups
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If ext2fs_descriptor_block_loc2() is called with a meta_bg filesystem
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and group_block is not the normal value, the function will return the
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location of the backup group descriptor block in the next block group.
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Unfortunately, it fails to account for the possibility that the backup
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group contains a backup superblock but the regular superblock does
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not. This is the case with block groups 48-49 on a meta_bg fs with 1k
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blocks; in this case, libext2fs will fail to open the filesystem.
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Therefore, teach the function to adjust for superblocks in the backup
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group, if necessary.
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Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
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Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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---
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lib/ext2fs/openfs.c | 19 +++++++++++++++----
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1 file changed, 15 insertions(+), 4 deletions(-)
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diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
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index 2c6e10e..b27bf19 100644
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--- a/lib/ext2fs/openfs.c
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+++ b/lib/ext2fs/openfs.c
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@@ -47,7 +47,7 @@ blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block,
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bg = EXT2_DESC_PER_BLOCK(fs->super) * i;
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if (ext2fs_bg_has_super(fs, bg))
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has_super = 1;
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- ret_blk = ext2fs_group_first_block2(fs, bg) + has_super;
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+ ret_blk = ext2fs_group_first_block2(fs, bg);
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/*
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* If group_block is not the normal value, we're trying to use
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* the backup group descriptors and superblock --- so use the
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@@ -57,10 +57,21 @@ blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block,
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* have the infrastructure in place to do that.
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*/
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if (group_block != fs->super->s_first_data_block &&
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- ((ret_blk + fs->super->s_blocks_per_group) <
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- ext2fs_blocks_count(fs->super)))
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+ ((ret_blk + has_super + fs->super->s_blocks_per_group) <
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+ ext2fs_blocks_count(fs->super))) {
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ret_blk += fs->super->s_blocks_per_group;
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- return ret_blk;
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+
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+ /*
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+ * If we're going to jump forward a block group, make sure
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+ * that we adjust has_super to account for the next group's
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+ * backup superblock (or lack thereof).
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+ */
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+ if (ext2fs_bg_has_super(fs, bg + 1))
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+ has_super = 1;
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+ else
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+ has_super = 0;
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+ }
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+ return ret_blk + has_super;
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}
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blk_t ext2fs_descriptor_block_loc(ext2_filsys fs, blk_t group_block, dgrp_t i)
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--
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2.17.1
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