Re: [PATCH 2/2] btrfs: lzo: Avoid decompressing obviously corrupted data

[Nikolay Borisov <nborisov@suse.com>]

On 15.05.2018 10:36, Qu Wenruo wrote:
> Unlike zlib decompression, lzo decompression doesn't need any
> initialization, thus we can't detect early corruption from
> initialization.
> 
> However for lzo compressed extent, its first 4bytes records the real
> unaligned compressed data size.
> We could use this as a clue, since any compressed extent should not
> exceed 128K, thus if we find such compressed data length, we are sure
> it's corrupted, then no need to continue decompression.
> 
> Normally, such problem won't really bother anyone, as compression relies
> on dataCoW and data csum, which means normally such corruption should be
> detect by data csum before going into compression.
> However due to a bug in compression condition, it's possible to create
> compressed extent without csum.
> 
> So we still need to do extra check for lzo just in case the compressed
> data is corrupted.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> lease note that, even with the binary dump of corrupted extent provided
> by the original reporter, James Harvey, I can only reproduce the "decompress
> failed" error message, but not the serious memory corruption followed.
> So there must be something missing, maybe we need to double check both
> btrfs lzo caller and kernel lzo lib.
> 
> But anyway, making btrfs lzo compression a little more robust is never a
> bad thing.
> ---
>  fs/btrfs/compression.h | 1 +
>  fs/btrfs/lzo.c         | 4 ++++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
> index cc605f7b23fb..317703d9b073 100644
> --- a/fs/btrfs/compression.h
> +++ b/fs/btrfs/compression.h
> @@ -6,6 +6,7 @@
>  #ifndef BTRFS_COMPRESSION_H
>  #define BTRFS_COMPRESSION_H
>  
> +#include <linux/sizes.h>

Stray include otherwise:

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

>  /*
>   * We want to make sure that amount of RAM required to uncompress an extent is
>   * reasonable, so we limit the total size in ram of a compressed extent to
> diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
> index 0667ea07f766..7ae2c0925770 100644
> --- a/fs/btrfs/lzo.c
> +++ b/fs/btrfs/lzo.c
> @@ -271,6 +271,10 @@ static int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
>  
>  	data_in = kmap(pages_in[0]);
>  	tot_len = read_compress_length(data_in);
> +	if (tot_len > BTRFS_MAX_COMPRESSED) {
> +		ret = -EIO;
> +		goto done;
> +	}
>  
>  	tot_in = LZO_LEN;
>  	in_offset = LZO_LEN;
>