[PATCH 3.16 051/245] btrfs: Check that each block group has corresponding chunk at mount time

Ben Hutchings
2020-04-23T23:21:06Z

From: Qu Wenruo <wqu@suse.com>

commit 514c7dca85a0bf40be984dab0b477403a6db901f upstream.

A crafted btrfs image with incorrect chunk<->block group mapping will
trigger a lot of unexpected things as the mapping is essential.

Although the problem can be caught by block group item checker
added in "btrfs: tree-checker: Verify block_group_item", it's still not
sufficient. A sufficiently valid block group item can pass the check
added by the mentioned patch but could fail to match the existing chunk.

This patch will add extra block group -> chunk mapping check, to ensure
we have a completely matching (start, len, flags) chunk for each block
group at mount time.

Here we reuse the original helper find_first_block_group(), which is
already doing the basic bg -> chunk checks, adding further checks of the
start/len and type flags.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=199837
Reported-by: Xu Wen <wen.xu@gatech.edu>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[bwh: Backported to 4.4: Use root->fs_info instead of fs_info]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/btrfs/extent-tree.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8556,6 +8556,8 @@ static int find_first_block_group(struct
int ret = 0;
struct btrfs_key found_key;
struct extent_buffer *leaf;
+ struct btrfs_block_group_item bg;
+ u64 flags;
int slot;

ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
@@ -8590,8 +8592,32 @@ static int find_first_block_group(struct
"logical %llu len %llu found bg but no related chunk",
found_key.objectid, found_key.offset);
ret = -ENOENT;
+ } else if (em->start != found_key.objectid ||
+ em->len != found_key.offset) {
+ btrfs_err(root->fs_info,
+ "block group %llu len %llu mismatch with chunk %llu len %llu",
+ found_key.objectid, found_key.offset,
+ em->start, em->len);
+ ret = -EUCLEAN;
} else {
- ret = 0;
+ read_extent_buffer(leaf, &bg,
+ btrfs_item_ptr_offset(leaf, slot),
+ sizeof(bg));
+ flags = btrfs_block_group_flags(&bg) &
+ BTRFS_BLOCK_GROUP_TYPE_MASK;
+
+ if (flags != (em->map_lookup->type &
+ BTRFS_BLOCK_GROUP_TYPE_MASK)) {
+ btrfs_err(root->fs_info,
+"block group %llu len %llu type flags 0x%llx mismatch with chunk type flags 0x%llx",
+ found_key.objectid,
+ found_key.offset, flags,
+ (BTRFS_BLOCK_GROUP_TYPE_MASK &
+ em->map_lookup->type));
+ ret = -EUCLEAN;
+ } else {
+ ret = 0;
+ }
}
free_extent_map(em);
goto out;