On Fri, May 11, 2018 at 01:35:27PM +0800, Qu Wenruo wrote:
> There are already 2 reports about strangely corrupted super blocks,
> where csum still matches but extra garbage gets slipped into super block.
>
> The corruption would looks like:
> --
> superblock: bytenr=65536, device=/dev/sdc1
> -
> csum_type 41700 (INVALID)
> csum0x3b252d3a [match]
> bytenr 65536
> flags 0x1
> ( WRITTEN )
> magic _BHRfS_M [match]
> ...
> incompat_flags 0x5b224169
> ( MIXED_BACKREF |
> COMPRESS_LZO |
> BIG_METADATA |
> EXTENDED_IREF |
> SKINNY_METADATA |
> unknown flag: 0x5b224000 )
> ...
> --
> Or
> --
> superblock: bytenr=65536, device=/dev/mapper/x
> -
> csum_type 35355 (INVALID)
> csum_size 32
> csum 0xf0dbeddd [match]
> bytenr 65536
> flags 0x1
>( WRITTEN )
> magic _BHRfS_M [match]
> ...
> incompat_flags 0x176d2169
>( MIXED_BACKREF |
> COMPRESS_LZO |
> BIG_METADATA |
> EXTENDED_IREF |
> SKINNY_METADATA |
> unknown flag: 0x176d2000 )
> --
>
> Obviously, csum_type and incompat_flags get some garbage, but its csum
> still matches, which means kernel calculates the csum based on corrupted
> super block memory.
> And after manually fixing these values, the filesystem is completely
> healthy without any problem exposed by btrfs check.
>
> Although the cause is still unknown, at least detect it and prevent further
> corruption.
>
> Reported-by: Ken Swenson
> Reported-by: Ben Parsons <9parso...@gmail.com>
> Signed-off-by: Qu Wenruo
> ---
> fs/btrfs/disk-io.c | 39 +++
> 1 file changed, 39 insertions(+)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index b981ecc4b6f9..985695074c51 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2610,6 +2610,41 @@ static int btrfs_validate_mount_super(struct
> btrfs_fs_info *fs_info)
> return __validate_super(fs_info, fs_info->super_copy, 0);
> }
>
> +/*
> + * Check the validation of super block at write time.
> + * Some checks like bytenr check will be skipped as their values will be
> + * overwritten soon.
> + * Extra checks like csum type and incompact flags will be executed here.
> + */
> +static int btrfs_validate_write_super(struct btrfs_fs_info *fs_info,
> + struct btrfs_super_block *sb)
> +{
> + int ret;
> +
> + ret = __validate_super(fs_info, sb, -1);
> + if (ret < 0)
> + goto out;
> + if (btrfs_super_csum_type(sb) != BTRFS_CSUM_TYPE_CRC32) {
> + ret = -EUCLEAN;
> + btrfs_err(fs_info, "invalid csum type, has %u want %u",
> + btrfs_super_csum_type(sb), BTRFS_CSUM_TYPE_CRC32);
> + goto out;
> + }
> + if (btrfs_super_incompat_flags(sb) & ~BTRFS_FEATURE_INCOMPAT_SUPP) {
> + ret = -EUCLEAN;
> + btrfs_err(fs_info,
> + "invalid incompact flags, has 0x%llu valid mask 0x%llu",
> + btrfs_super_incompat_flags(sb),
> + BTRFS_FEATURE_INCOMPAT_SUPP);
I think you need (unsigned long long) here as
BTRFS_FEATURE_INCOMPAT_SUPP do not have a type. I'll fix that.
Reviewed-by: David Sterba
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