Re: [PATCH] hfsplus: fix concurrent acess of alloc_blocks

[sougata santra]

On 02/19/2014 12:06 AM, Andrew Morton wrote:
> On Mon, 17 Feb 2014 14:20:47 +0200 Sougata Santra <sougata@xxxxxxxxxx> wrote:
>
> > Concurrent access to alloc_blocks in hfsplus_inode_info is
> > protected by extents_lock mutex. This patch fixes two
> > instances where alloc_blocks modification was not protected
> > with this lock. This fixes possible allocation bitmap
> > corruption in race conditions while extending and truncating
> > files.
> >
> > ...
> >
> > --- a/fs/hfsplus/extents.c
> > +++ b/fs/hfsplus/extents.c
> > @@ -498,11 +498,13 @@ int hfsplus_file_extend(struct inode *inode)
> >   			goto insert_extent;
> >   	}
> >   out:
> > -	mutex_unlock(&hip->extents_lock);
> >   	if (!res) {
> >   		hip->alloc_blocks += len;
> > +		mutex_unlock(&hip->extents_lock);
> >   		hfsplus_mark_inode_dirty(inode, HFSPLUS_I_ALLOC_DIRTY);
> > +		return 0;
> >   	}
> > +	mutex_unlock(&hip->extents_lock);
> >   	return res;
>
> This looks OK.
>
> > @@ -592,9 +594,9 @@ void hfsplus_file_truncate(struct inode *inode)
> >   		hfs_brec_remove(&fd);
> >   	}
> >   	hfs_find_exit(&fd);
> > -	mutex_unlock(&hip->extents_lock);
> >
> >   	hip->alloc_blocks = blk_cnt;
> > +	mutex_unlock(&hip->extents_lock);
> >   out:
> >   	hip->phys_size = inode->i_size;
> >   	hip->fs_blocks = (inode->i_size + sb->s_blocksize - 1) >>
>
> But this does not.  To provide locking for
> hfsplus_inode_info.alloc_blocks, we must take the lock *before* taking
> a local copy of ->alloc_blocks.
>
> Please review:
>
> --- a/fs/hfsplus/extents.c~hfsplus-fix-concurrent-acess-of-alloc_blocks-fix
> +++ a/fs/hfsplus/extents.c
> @@ -556,11 +556,13 @@ void hfsplus_file_truncate(struct inode
>
>   	blk_cnt = (inode->i_size + HFSPLUS_SB(sb)->alloc_blksz - 1) >>
>   			HFSPLUS_SB(sb)->alloc_blksz_shift;
> +
> +	mutex_lock(&hip->extents_lock);
> +
>   	alloc_cnt = hip->alloc_blocks;
>   	if (blk_cnt == alloc_cnt)
> -		goto out;
> +		goto out_unlock;
>
> -	mutex_lock(&hip->extents_lock);
>   	res = hfs_find_init(HFSPLUS_SB(sb)->ext_tree, &fd);
>   	if (res) {
>   		mutex_unlock(&hip->extents_lock);
> @@ -594,6 +596,7 @@ void hfsplus_file_truncate(struct inode
>   	hfs_find_exit(&fd);
>
>   	hip->alloc_blocks = blk_cnt;
> +out_unlock:
>   	mutex_unlock(&hip->extents_lock);
>   out:
We can also remove this label ?
>   	hip->phys_size = inode->i_size;
> _

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/