Patchwork [36/74] libext2fs: detect

login
register
mail settings
Submitter Darrick J. Wong
Date Dec. 11, 2013, 1:22 a.m.
Message ID <20131211012220.30655.26226.stgit@birch.djwong.org>
Download mbox | patch
Permalink /patch/299705/
State Accepted
Headers show

Comments

Darrick J. Wong - Dec. 11, 2013, 1:22 a.m.
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@oracle.com>
---
 lib/ext2fs/openfs.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)



--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Theodore Ts'o - Dec. 13, 2013, 4:39 a.m.
It looks like the subject line for this commit was truncated --- I
could try to make something up, but could you suggest something?

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@oracle.com>
> ---
>  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)
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Darrick J. Wong - Jan. 15, 2014, 9 p.m.
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@oracle.com>
> > ---
> >  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)
> > 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

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)