On Thu, Feb 04, 2021 at 12:09:31PM -0800, Boris Burkov wrote:
Hi Boris, I have a question for this code.
> btrfs-corrupt-block already has a mix of generic and specific corruption
> options, but currently lacks the capacity for totally arbitrary
> corruption in item data.
>
> There is already a flag for corruption size (bytes/-b), so add a flag
> for an offset and a value to memset the item with. Exercise the new
> flags with a new variant for -I (item) corruption. Look up the item as
> before, but instead of corrupting a field in the item struct, corrupt an
> offset/size in the item data.
>
> The motivating example for this is that in testing fsverity with btrfs,
> we need to corrupt the generated Merkle tree--metadata item data which
> is an opaque blob to btrfs.
>
> Signed-off-by: Boris Burkov <bo...@bur.io>
> ---
> btrfs-corrupt-block.c | 71 +++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 68 insertions(+), 3 deletions(-)
>
> diff --git a/btrfs-corrupt-block.c b/btrfs-corrupt-block.c
> index 0c022a8e..bf1ce9c5 100644
> --- a/btrfs-corrupt-block.c
> +++ b/btrfs-corrupt-block.c
> @@ -116,11 +116,13 @@ static void print_usage(int ret)
> printf("\t-m The metadata block to corrupt (must also specify -f for
> the field to corrupt)\n");
> printf("\t-K <u64,u8,u64> Corrupt the given key (must also specify -f
> for the field and optionally -r for the root)\n");
> printf("\t-f The field in the item to corrupt\n");
> - printf("\t-I <u64,u8,u64> Corrupt an item corresponding to the passed
> key triplet (must also specify the field to corrupt and root for the
> item)\n");
> + printf("\t-I <u64,u8,u64> Corrupt an item corresponding to the passed
> key triplet (must also specify the field, or bytes, offset, and value to
> corrupt and root for the item)\n");
> printf("\t-D <u64,u8,u64> Corrupt a dir item corresponding to the
> passed key triplet, must also specify a field\n");
> printf("\t-d <u64,u8,u64> Delete item corresponding to passed key
> triplet\n");
> printf("\t-r Operate on this root\n");
> printf("\t-C Delete a csum for the specified bytenr. When used with
> -b it'll delete that many bytes, otherwise it's just sectorsize\n");
> + printf("\t-v Value to use for corrupting item data\n");
> + printf("\t-o Offset to use for corrupting item data\n");
> exit(ret);
> }
>
> @@ -896,6 +898,50 @@ out:
> return ret;
> }
>
> +static int corrupt_btrfs_item_data(struct btrfs_root *root,
> + struct btrfs_key *key,
> + u64 bogus_offset, u64 bogus_size,
> + char bogus_value)
> +{
> + struct btrfs_trans_handle *trans;
> + struct btrfs_path *path;
> + int ret;
> + void *data;
> + struct extent_buffer *leaf;
> + int slot;
> +
> + path = btrfs_alloc_path();
> + if (!path)
> + return -ENOMEM;
> +
> + trans = btrfs_start_transaction(root, 1);
> + if (IS_ERR(trans)) {
> + fprintf(stderr, "Couldn't start transaction %ld\n",
> + PTR_ERR(trans));
> + ret = PTR_ERR(trans);
> + goto free_path;
> + }
> +
> + ret = btrfs_search_slot(trans, root, key, path, 0, 1);
> + if (ret != 0) {
> + fprintf(stderr, "Error searching to node %d\n", ret);
> + goto commit_txn;
This is error case. but this code goes to commit transaction. I think there is
an option to abort transaction. This code has pros than aborting?
> + }
> + leaf = path->nodes[0];
> + slot = path->slots[0];
> + data = btrfs_item_ptr(leaf, slot, void);
> + // TODO: check offset/size legitimacy
> + data += bogus_offset;
> + memset_extent_buffer(leaf, bogus_value, (unsigned long)data,
> bogus_size);
> + btrfs_mark_buffer_dirty(leaf);
> +
> +commit_txn:
> + btrfs_commit_transaction(trans, root);
> +free_path:
> + btrfs_free_path(path);
> + return ret;
> +}
> +
> static int delete_item(struct btrfs_root *root, struct btrfs_key *key)
> {
> struct btrfs_trans_handle *trans;
> @@ -1151,6 +1197,8 @@ int main(int argc, char **argv)
> u64 root_objectid = 0;
> u64 csum_bytenr = 0;
> char field[FIELD_BUF_LEN];
> + u64 bogus_value = (u64)-1;
> + u64 bogus_offset = (u64)-1;
>
> field[0] = '\0';
> memset(&key, 0, sizeof(key));
> @@ -1177,11 +1225,13 @@ int main(int argc, char **argv)
> { "delete", no_argument, NULL, 'd'},
> { "root", no_argument, NULL, 'r'},
> { "csum", required_argument, NULL, 'C'},
> + { "value", required_argument, NULL, 'v'},
> + { "offset", required_argument, NULL, 'o'},
> { "help", no_argument, NULL, GETOPT_VAL_HELP},
> { NULL, 0, NULL, 0 }
> };
>
> - c = getopt_long(argc, argv, "l:c:b:eEkuUi:f:x:m:K:I:D:d:r:C:",
> + c = getopt_long(argc, argv,
> "l:c:b:eEkuUi:f:x:m:K:I:D:d:r:C:v:o:",
> long_options, NULL);
> if (c < 0)
> break;
> @@ -1244,6 +1294,12 @@ int main(int argc, char **argv)
> case 'C':
> csum_bytenr = arg_strtou64(optarg);
> break;
> + case 'v':
> + bogus_value = arg_strtou64(optarg);
> + break;
> + case 'o':
> + bogus_offset = arg_strtou64(optarg);
> + break;
> case GETOPT_VAL_HELP:
> default:
> print_usage(c != GETOPT_VAL_HELP);
> @@ -1368,7 +1424,16 @@ int main(int argc, char **argv)
> if (!root_objectid)
> print_usage(1);
>
> - ret = corrupt_btrfs_item(target_root, &key, field);
> + if (*field != 0)
> + ret = corrupt_btrfs_item(target_root, &key, field);
> + else if (bogus_offset != (u64)-1 &&
> + bytes != (u64)-1 &&
> + bogus_value != (u64)-1)
> + ret = corrupt_btrfs_item_data(target_root, &key,
> + bogus_offset, bytes,
> + bogus_value);
> + else
> + print_usage(1);
> goto out_close;
> }
> if (delete) {
> --
> 2.24.1
>
