Ping.
Is there any reason why the btrfs progs (except for btrfs-show-super)
don't validate the super block's checksum?
thanks
On Mon, Jun 10, 2013 at 8:51 PM, Filipe David Borba Manana
<fdman...@gmail.com> wrote:
> After finding a super block in a device also validate its
> checksum. This validation is done in the kernel but it was
> missing in btrfs-progs.
>
> The function btrfs_check_super_csum() is imported from the
> file fs/btrfs/disk-io.c in the kernel source tree.
>
> Signed-off-by: Filipe David Borba Manana <fdman...@gmail.com>
> ---
> disk-io.c | 76
> +++++++++++++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 62 insertions(+), 14 deletions(-)
>
> diff --git a/disk-io.c b/disk-io.c
> index bd9cf4e..edd4d52 100644
> --- a/disk-io.c
> +++ b/disk-io.c
> @@ -1085,47 +1085,95 @@ struct btrfs_root *open_ctree_fd(int fp, const char
> *path, u64 sb_bytenr,
> return info->fs_root;
> }
>
> +static int btrfs_check_super_csum(char *raw_disk_sb)
> +{
> + struct btrfs_super_block *disk_sb =
> + (struct btrfs_super_block *)raw_disk_sb;
> + u16 csum_type = btrfs_super_csum_type(disk_sb);
> + int ret = 0;
> +
> + if (csum_type == BTRFS_CSUM_TYPE_CRC32) {
> + u32 crc = ~(u32)0;
> + const int csum_size = sizeof(crc);
> + char result[csum_size];
> +
> + /*
> + * The super_block structure does not span the whole
> + * BTRFS_SUPER_INFO_SIZE range, we expect that the unused
> space
> + * is filled with zeros and is included in the checkum.
> + */
> + crc = btrfs_csum_data(NULL, raw_disk_sb + BTRFS_CSUM_SIZE,
> + crc, BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
> + btrfs_csum_final(crc, result);
> +
> + if (memcmp(raw_disk_sb, result, csum_size))
> + ret = 1;
> +
> + if (ret && btrfs_super_generation(disk_sb) < 10) {
> + fprintf(stderr, "btrfs: super block crcs don't match,
> "
> + "older mkfs detected\n");
> + ret = 0;
> + }
> + }
> +
> + if (csum_type >= ARRAY_SIZE(btrfs_csum_sizes)) {
> + fprintf(stderr, "btrfs: unsupported checksum algorithm %u\n",
> + csum_type);
> + ret = 1;
> + }
> +
> + return ret;
> +}
> +
> int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
> {
> u8 fsid[BTRFS_FSID_SIZE];
> int fsid_is_initialized = 0;
> - struct btrfs_super_block buf;
> + char buf[BTRFS_SUPER_INFO_SIZE];
> + struct btrfs_super_block *tmp_sb;
> int i;
> int ret;
> u64 transid = 0;
> u64 bytenr;
>
> if (sb_bytenr != BTRFS_SUPER_INFO_OFFSET) {
> - ret = pread64(fd, &buf, sizeof(buf), sb_bytenr);
> + ret = pread64(fd, buf, sizeof(buf), sb_bytenr);
> if (ret < sizeof(buf))
> return -1;
>
> - if (btrfs_super_bytenr(&buf) != sb_bytenr ||
> - buf.magic != cpu_to_le64(BTRFS_MAGIC))
> + tmp_sb = (struct btrfs_super_block *)buf;
> +
> + if (btrfs_super_bytenr(tmp_sb) != sb_bytenr ||
> + tmp_sb->magic != cpu_to_le64(BTRFS_MAGIC) ||
> + btrfs_check_super_csum(buf))
> return -1;
>
> - memcpy(sb, &buf, sizeof(*sb));
> + memcpy(sb, buf, sizeof(*sb));
> return 0;
> }
>
> for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
> bytenr = btrfs_sb_offset(i);
> - ret = pread64(fd, &buf, sizeof(buf), bytenr);
> + ret = pread64(fd, buf, sizeof(buf), bytenr);
> if (ret < sizeof(buf))
> break;
>
> - if (btrfs_super_bytenr(&buf) != bytenr )
> + tmp_sb = (struct btrfs_super_block *)buf;
> +
> + if (btrfs_super_bytenr(tmp_sb) != bytenr )
> continue;
> /* if magic is NULL, the device was removed */
> - if (buf.magic == 0 && i == 0)
> + if (tmp_sb->magic == 0 && i == 0)
> return -1;
> - if (buf.magic != cpu_to_le64(BTRFS_MAGIC))
> + if (tmp_sb->magic != cpu_to_le64(BTRFS_MAGIC))
> + continue;
> + if (btrfs_check_super_csum(buf))
> continue;
>
> if (!fsid_is_initialized) {
> - memcpy(fsid, buf.fsid, sizeof(fsid));
> + memcpy(fsid, tmp_sb->fsid, sizeof(fsid));
> fsid_is_initialized = 1;
> - } else if (memcmp(fsid, buf.fsid, sizeof(fsid))) {
> + } else if (memcmp(fsid, tmp_sb->fsid, sizeof(fsid))) {
> /*
> * the superblocks (the original one and
> * its backups) contain data of different
> @@ -1134,9 +1182,9 @@ int btrfs_read_dev_super(int fd, struct
> btrfs_super_block *sb, u64 sb_bytenr)
> continue;
> }
>
> - if (btrfs_super_generation(&buf) > transid) {
> - memcpy(sb, &buf, sizeof(*sb));
> - transid = btrfs_super_generation(&buf);
> + if (btrfs_super_generation(tmp_sb) > transid) {
> + memcpy(sb, buf, sizeof(*sb));
> + transid = btrfs_super_generation(tmp_sb);
> }
> }
>
> --
> 1.7.9.5
>
--
Filipe David Manana,
"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
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