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

Qu Wenruo
2019-12-18T01:20:02Z

[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)
continue;

--
2.24.1