On Thu, 26 Mar 2020 13:35:56 +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:
>
> 1fe0: 4cdc 02fc 0bfd 02c0 dc02 0d13 0100 0001 L...
> 1ff0: 0008 0300 0011 |
> 2000: 4705 0001 cc02 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 0x0547 (88539136), other than the expected result
> 0x0547 (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
> Cc: Marek Behun
> ---
> fs/btrfs/compression.c | 20 +++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index 4ef44ce11485..b1884fc15ee0 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -9,6 +9,7 @@
> #include
> #include
> #include
> +#include
> #include
> #include
>
> @@ -16,7 +17,7 @@
> #define LZO_LEN 4
> static u32 decompress_lzo(const u8 *cbuf, u32 clen, u8 *dbuf, u32 dlen)
> {
> - u32 tot_len, in_len, res;
> + u32 tot_len, tot_in, in_len, res;
> size_t out_len;
> int ret;
>
> @@ -24,9 +25,11 @@ static u32 decompress_lzo(const u8 *cbuf, u32 clen, u8
> *dbuf, u32 dlen)
> return -1;
>
> tot_len = le32_to_cpu(get_unaligned((u32 *)cbuf));
> + tot_in = 0;
> cbuf += LZO_LEN;
> clen -= LZO_LEN;
> tot_len -= LZO_LEN;
> + tot_in += LZO_LEN;
>
> if (tot_len == 0 && dlen)
> return -1;
> @@ -36,6 +39,8 @@ static u32 decompress_lzo(const u8 *cbuf, u32 clen, u8
> *dbuf, u32 dlen)
> res = 0;
>
> while (tot_len > LZO_LEN) {
> + u32 rem_page;
> +
> in_len = le32_to_cpu(get_unaligned((u32 *)cbuf));
> cbuf += LZO_LEN;
> clen -= LZO_LEN;
> @@ -44,6 +49,7 @@ static u32 decompress_lzo(const u8 *cbuf, u32 clen, u8
> *dbuf, u32 dlen)
> return -1;
>
> tot_len -= (LZO_LEN + in_len);
> + tot_in += (LZO_LEN + in_len);
>
> out_len = dlen;
> ret = lzo1x_decompress_safe(cbuf, in_len, dbuf, _len);
> @@ -56,6 +62,18 @@ static u32 decompress_lzo(const u8 *cbuf, u32 clen, u8
> *dbuf, u32 dlen)
> dlen -= out_len;
>
> res += out_len;
> +
> + /*
> + * If the 4 bytes header does not fit to the rest of the page we
> + * have to move to next one, or we read some garbage.
> + */
> + rem_page = PAGE_SIZE - (tot_in % PAGE_SIZE);
> + if (rem_page < LZO_LEN) {
> + cbuf += rem_page;
> + tot_in += rem_page;
> + clen -= rem_page;
> + tot_len -= rem_page;
> + }
> }
>
> return res;
Reviewed-by: Marek Behún
