Re: [PATCH 6/6] btrfs-progs: extent-tree: Fix a by-one error in exclude_super_stripes()

David Sterba
2020-01-02T16:56:15Z

On Wed, Dec 18, 2019 at 09:19:42AM +0800, Qu Wenruo wrote:
> [BUG]
> For certain btrfs images, a BUG_ON() can be triggered at open_ctree()
> time:
> Opening filesystem to check...
> extent_io.c:158: insert_state: BUG_ON `end < start` triggered, value 1
> btrfs(+0x2de57)[0x560c4d7cfe57]
> btrfs(+0x2e210)[0x560c4d7d0210]
> btrfs(set_extent_bits+0x254)[0x560c4d7d0854]
> btrfs(exclude_super_stripes+0xbf)[0x560c4d7c65ff]
> btrfs(btrfs_read_block_groups+0x29d)[0x560c4d7c698d]
> btrfs(btrfs_setup_all_roots+0x3f3)[0x560c4d7c0b23]
> btrfs(+0x1ef53)[0x560c4d7c0f53]
> btrfs(open_ctree_fs_info+0x90)[0x560c4d7c11a0]
> btrfs(+0x6d3f9)[0x560c4d80f3f9]
> btrfs(main+0x94)[0x560c4d7b60c4]
> /usr/lib/libc.so.6(__libc_start_main+0xf3)[0x7fd189773ee3]
> btrfs(_start+0x2e)[0x560c4d7b635e]
>
> [CAUSE]
> This is caused by passing @len == 0 to add_excluded_extent(), which
> means one revsere mapped range is just out of the block group range,
> normally means a by-one error.
>
> [FIX]
> Fix the boundary check on the reserve mapped range against block group
> range.
> If a reverse mapped super block starts at the end of the block group, it
> doesn't cover so we don't need to bother the case.
>
> Issue: #210
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> extent-tree.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/extent-tree.c b/extent-tree.c
> index 6288c8a3..7ba80375 100644
> --- a/extent-tree.c
> +++ b/extent-tree.c
> @@ -3640,7 +3640,7 @@ int exclude_super_stripes(struct btrfs_fs_info *fs_info,
> while (nr--) {
> u64 start, len;
>
> - if (logical[nr] > cache->key.objectid +
> + if (logical[nr] >= cache->key.objectid +
> cache->key.offset)

Do we have the same problem in kernel? The code does ">".