On Thu, Dec 12, 2013 at 11:39:38PM -0500, Theodore Ts'o wrote:
> It looks like the subject line for this commit was truncated --- I
> could try to make something up, but could you suggest something?
I have no recollection if I ever sent a reply to this, but the subject line
should be:
"libext2fs: detect superblock when jumping ahead trying to read gdt"
--D
>
> Thanks!!
>
> - Ted
>
>
> On Tue, Dec 10, 2013 at 05:22:20PM -0800, Darrick J. Wong wrote:
> > If ext2fs_descriptor_block_loc2() is called with a meta_bg filesystem
> > and group_block is not the normal value, the function will return the
> > location of the backup group descriptor block in the next block group.
> > Unfortunately, it fails to account for the possibility that the backup
> > group contains a backup superblock but the regular superblock does
> > not. This is the case with block groups 48-49 on a meta_bg fs with 1k
> > blocks; in this case, libext2fs will fail to open the filesystem.
> >
> > Therefore, teach the function to adjust for superblocks in the backup
> > group, if necessary.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > lib/ext2fs/openfs.c | 19 +++++++++++++++----
> > 1 file changed, 15 insertions(+), 4 deletions(-)
> >
> >
> > diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
> > index b2a8abb..92d9e40 100644
> > --- a/lib/ext2fs/openfs.c
> > +++ b/lib/ext2fs/openfs.c
> > @@ -47,7 +47,7 @@ blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block,
> > bg = EXT2_DESC_PER_BLOCK(fs->super) * i;
> > if (ext2fs_bg_has_super(fs, bg))
> > has_super = 1;
> > - ret_blk = ext2fs_group_first_block2(fs, bg) + has_super;
> > + ret_blk = ext2fs_group_first_block2(fs, bg);
> > /*
> > * If group_block is not the normal value, we're trying to use
> > * the backup group descriptors and superblock --- so use the
> > @@ -57,10 +57,21 @@ blk64_t ext2fs_descriptor_block_loc2(ext2_filsys fs, blk64_t group_block,
> > * have the infrastructure in place to do that.
> > */
> > if (group_block != fs->super->s_first_data_block &&
> > - ((ret_blk + fs->super->s_blocks_per_group) <
> > - ext2fs_blocks_count(fs->super)))
> > + ((ret_blk + has_super + fs->super->s_blocks_per_group) <
> > + ext2fs_blocks_count(fs->super))) {
> > ret_blk += fs->super->s_blocks_per_group;
> > - return ret_blk;
> > +
> > + /*
> > + * If we're going to jump forward a block group, make sure
> > + * that we adjust has_super to account for the next group's
> > + * backup superblock (or lack thereof).
> > + */
> > + if (ext2fs_bg_has_super(fs, bg + 1))
> > + has_super = 1;
> > + else
> > + has_super = 0;
> > + }
> > + return ret_blk + has_super;
> > }
> >
> > blk_t ext2fs_descriptor_block_loc(ext2_filsys fs, blk_t group_block, dgrp_t i)
> >
> --
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