Re: [PATCH U-BOOT v2 3/3] fs: btrfs: Fix LZO false decompression error caused by pending zero

[Tom Rini <trini@konsulko.com>]

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On Thu, Mar 26, 2020 at 01:35:56PM +0800, Qu Wenruo wrote:

> For certain btrfs files with compressed file extent, uboot will fail to
> load it:
> 
>   btrfs_read_extent_reg: disk_bytenr=14229504 disk_len=73728 offset=0 nr_bytes=131
>   072
>   decompress_lzo: tot_len=70770
>   decompress_lzo: in_len=1389
>   decompress_lzo: in_len=2400
>   decompress_lzo: in_len=3002
>   decompress_lzo: in_len=1379
>   decompress_lzo: in_len=88539136
>   decompress_lzo: header error, in_len=88539136 clen=65534 tot_len=62580
> 
> NOTE: except the last line, all other lines are debug output.
> 
> Btrfs lzo compression uses its own format to record compressed size
> (segment header, LE32).
> 
> However to make decompression easier, we never put such segment header
> across page boundary.
> 
> In above case, the xxd dump of the lzo compressed data looks like this:
> 
> 00001fe0: 4cdc 02fc 0bfd 02c0 dc02 0d13 0100 0001  L...............
> 00001ff0: 0000 0008 0300 0000 0000 0011 0000|0000  ................
> 00002000: 4705 0000 0001 cc02 0000 0000 0000 1e01  G...............
> 
> '|' is the "expected" segment header start position.
> 
> But in that page, there are only 2 bytes left, can't contain the 4 bytes
> segment header.
> 
> So btrfs compression will skip that 2 bytes, put the segment header in
> next page directly.
> 
> Uboot doesn't have such check, and read the header with 2 bytes offset,
> result 0x05470000 (88539136), other than the expected result
> 0x00000547 (1351), resulting above error.
> 
> Follow the btrfs-progs restore implementation, by introducing tot_in to
> record total processed bytes (including headers), and do proper page
> boundary skip to fix it.
> 
> Please note that, current code base doesn't parse fs_info thus we can't
> grab sector size easily, so it uses PAGE_SIZE, and relying on fs open
> time check to exclude unsupported sector size.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> Cc: Marek Behun <marek.behun@nic.cz>
> Reviewed-by: Marek Behún <marek.behun@nic.cz>

Applied to u-boot/master, thanks!

-- 
Tom

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