Re: [PATCH 5/5] btrfs: ctree: Checking key orders before merged tree blocks

Nikolay Borisov
2019-07-10T11:19:34Z

On 10.07.19 г. 11:02 ч., Qu Wenruo wrote:
> [BUG]
> With crafted image, btrfs can panic at btrfs_del_csums().
> kernel BUG at fs/btrfs/ctree.c:3188!
> invalid opcode: 0000 [#1] SMP PTI
> CPU: 0 PID: 1156 Comm: btrfs-transacti Not tainted 5.0.0-rc8+ #9
> RIP: 0010:btrfs_set_item_key_safe+0x16c/0x180
> Code: b7 48 8d 7d bf 4c 89 fe 48 89 45 c8 0f b6 45 b6 88 45 c7 48 8b 45 ae 48 89 45 bf e8 ce f2 ff ff 85 c0 0f 8f 48 ff ff ff 0f 0b <0f> 0b e8 dd 8d be ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 66 66
> RSP: 0018:ffff976141257ab8 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: ffff898a6b890930 RCX: 0000000004b70000
> RDX: 0000000000000000 RSI: ffff976141257bae RDI: ffff976141257acf
> RBP: ffff976141257b10 R08: 0000000000001000 R09: ffff9761412579a8
> R10: 0000000000000000 R11: 0000000000000000 R12: ffff976141257abe
> R13: 0000000000000003 R14: ffff898a6a8be578 R15: ffff976141257bae
> FS: 0000000000000000(0000) GS:ffff898a77a00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f779d9cd624 CR3: 000000022b2b4006 CR4: 00000000000206f0
> Call Trace:
> truncate_one_csum+0xac/0xf0
> btrfs_del_csums+0x24f/0x3a0
> __btrfs_free_extent.isra.72+0x5a7/0xbe0
> __btrfs_run_delayed_refs+0x539/0x1120
> btrfs_run_delayed_refs+0xdb/0x1b0
> btrfs_commit_transaction+0x52/0x950
> ? start_transaction+0x94/0x450
> transaction_kthread+0x163/0x190
> kthread+0x105/0x140
> ? btrfs_cleanup_transaction+0x560/0x560
> ? kthread_destroy_worker+0x50/0x50
> ret_from_fork+0x35/0x40
> Modules linked in:
> ---[ end trace 93bf9db00e6c374e ]---
>
> [CAUSE]
> This crafted image has a very tricky key order corruption:
>
> checksum tree key (CSUM_TREE ROOT_ITEM 0)
> node 29741056 level 1 items 14 free 107 generation 19 owner CSUM_TREE
> ...
> key (EXTENT_CSUM EXTENT_CSUM 73785344) block 29757440 gen 19
> key (EXTENT_CSUM EXTENT_CSUM 77594624) block 29753344 gen 19
> ...
>
> leaf 29757440 items 5 free space 150 generation 19 owner CSUM_TREE
> item 0 key (EXTENT_CSUM EXTENT_CSUM 73785344) itemoff 2323 itemsize 1672
> range start 73785344 end 75497472 length 1712128
> item 1 key (EXTENT_CSUM EXTENT_CSUM 75497472) itemoff 2319 itemsize 4
> range start 75497472 end 75501568 length 4096
> item 2 key (EXTENT_CSUM EXTENT_CSUM 75501568) itemoff 579 itemsize 1740
> range start 75501568 end 77283328 length 1781760
> item 3 key (EXTENT_CSUM EXTENT_CSUM 77283328) itemoff 575 itemsize 4
> range start 77283328 end 77287424 length 4096
> item 4 key (EXTENT_CSUM EXTENT_CSUM 4120596480) itemoff 275 itemsize 300 <<<
> range start 4120596480 end 4120903680 length 307200
> leaf 29753344 items 3 free space 1936 generation 19 owner CSUM_TREE
> item 0 key (18446744073457893366 EXTENT_CSUM 77594624) itemoff 2323 itemsize 1672
> range start 77594624 end 79306752 length 1712128
> ...
>
> Note the item 4 key of leaf 29757440, which is obviously too large, and
> even larger than the first key of the next leaf.
>
> However it still follows the key order in that tree block, thus tree
> checker is unable to detect it at read time, since tree checker can only
> work inside a leaf, thus such complex corruption can't be rejected in
> advance.
>
> [FIX]
> The next timing to detect such problem is at tree block merge time,
> which is in push_node_left(), balance_node_right(), push_leaf_left() and
> push_leaf_right().
>
> Now we check if the key order of the right most key of the left node is
> larger than the left most key of the right node.
>
> By this we don't need to call the full tree-check, while still keeps the
> key order correct as key order in each node is already checked by tree
> checker thus we only need to check the above two slots.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202833
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>, albeit see below for
some minors suggestions (feel free to ignore).

> ---
> fs/btrfs/ctree.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 63 insertions(+)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 5df76c17775a..38118e050689 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -3219,6 +3219,52 @@ void btrfs_set_item_key_safe(struct btrfs_fs_info *fs_info,
> fixup_low_keys(path, &disk_key, 1);
> }
>
> +/*
> + * Check the cross tree block key ordering.
> + *
> + * Tree-checker only works inside one tree block, thus the following
> + * corruption can not be rejected by tree-checker:
> + * Leaf @left | Leaf @right
> + * --------------------------------------------------------------
> + * | 1 | 2 | 3 | 4 | 5 | f6 | | 7 | 8 |
> + *
> + * Key f6 in leaf @left itself is valid, but not valid when the next
> + * key in leaf @right is 7.
> + * This can only be checked at tree block merge time.
> + * And since tree checker has ensured all key order in each tree block
> + * is correct, we only need to bother the last key of @left and the first
> + * key of @right.
> + */
> +static int check_cross_tree_key_order(struct extent_buffer *left,
> + struct extent_buffer *right)
> +{
> + struct btrfs_key left_last;
> + struct btrfs_key right_first;
> + int level = btrfs_header_level(left);
> + int nr_left = btrfs_header_nritems(left);
> + int nr_right = btrfs_header_nritems(right);
> +
> + /* No key to check in one of the tree blocks */
> + if (!nr_left || !nr_right)
> + return 0;
> + if (level) {
> + btrfs_node_key_to_cpu(left, &left_last, nr_left - 1);
> + btrfs_node_key_to_cpu(right, &right_first, 0);
> + } else {
> + btrfs_item_key_to_cpu(left, &left_last, nr_left - 1);
> + btrfs_item_key_to_cpu(right, &right_first, 0);
> + }
> + if (btrfs_comp_cpu_keys(&left_last, &right_first) >= 0) {
> + btrfs_crit(left->fs_info,
> +"bad key order cross tree blocks, left last (%llu %u %llu) right first (%llu %u %llu",
> + left_last.objectid, left_last.type,
> + left_last.offset, right_first.objectid,
> + right_first.type, right_first.offset);
> + return -EUCLEAN;
> + }
> + return 0;
> +}
> +

nit: I wonder if it will make it a bit easier to reason about the code
if that function is renamed to valid_cross_block_key_order and make it
return true or false, then it's callers will do if
(!valid_cross_block_key_ordered) {
return -EUCLEAN
}

I guess it won't be much different than it is now.

> /*
> * try to push data from one node into the next node left in the
> * tree.
> @@ -3263,6 +3309,10 @@ static int push_node_left(struct btrfs_trans_handle *trans,
> } else
> push_items = min(src_nritems - 8, push_items);
>
> + /* dst is the left eb src is the middle eb */
nit: missing ',' between 'eb' and 'src'. But this is very minor.

> + ret = check_cross_tree_key_order(dst, src);
> + if (ret < 0)
> + return ret;
> ret = tree_mod_log_eb_copy(dst, src, dst_nritems, 0, push_items);
> if (ret) {
> btrfs_abort_transaction(trans, ret);
> @@ -3331,6 +3381,10 @@ static int balance_node_right(struct btrfs_trans_handle *trans,
> if (max_push < push_items)
> push_items = max_push;
>
> + /* dst is the right eb, src is the middle eb */
> + ret = check_cross_tree_key_order(src, dst);
> + if (ret < 0)
> + return ret;
> ret = tree_mod_log_insert_move(dst, push_items, 0, dst_nritems);
> BUG_ON(ret < 0);
> memmove_extent_buffer(dst, btrfs_node_key_ptr_offset(push_items),
> @@ -3810,6 +3864,12 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
> if (left_nritems == 0)
> goto out_unlock;
>
> + ret = check_cross_tree_key_order(left, right);
> + if (ret < 0) {
> + btrfs_tree_unlock(right);
> + free_extent_buffer(right);
> + return ret;
> + }
> if (path->slots[0] == left_nritems && !empty) {
> /* Key greater than all keys in the leaf, right neighbor has
> * enough room for it and we're not emptying our leaf to delete
> @@ -4048,6 +4108,9 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
> goto out;
> }
>
> + ret = check_cross_tree_key_order(left, right);
> + if (ret < 0)
> + goto out;
> return __push_leaf_left(path, min_data_size,
> empty, left, free_space, right_nritems,
> max_slot);
>