Re: [PATCH] XZ decompressor: Fix decoding of empty LZMA2 streams

Andrew Morton
2011-05-03T21:36:43Z

On Sun, 1 May 2011 19:38:42 +0300
Lasse Collin <lasse.collin@tukaani.org> wrote:

> From: Lasse Collin <lasse.collin@tukaani.org>
>
> The old code considered valid empty LZMA2 streams to be corrupt.
> Note that a typical empty .xz file has no LZMA2 data at all,
> and thus most .xz files having no uncompressed data are handled
> correctly even without this fix.
>
> Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>

The patch didn't have the cc:stable tag, but appears to be needed in
2.6.38.x and perhaps earlier, yes?

It's commit 646032e3b05b32d3f20cb108a030593d9d792eb5 in mainline.

>
> lib/xz/xz_dec_lzma2.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff -uprN linux-2.6.39-rc5-git5.orig/lib/xz/xz_dec_lzma2.c linux-2.6.39-rc5-git5/lib/xz/xz_dec_lzma2.c
> --- linux-2.6.39-rc5-git5.orig/lib/xz/xz_dec_lzma2.c 2011-05-01 17:56:38.000000000 +0300
> +++ linux-2.6.39-rc5-git5/lib/xz/xz_dec_lzma2.c 2011-05-01 18:06:03.000000000 +0300
> @@ -969,6 +969,9 @@ XZ_EXTERN enum xz_ret xz_dec_lzma2_run(s
> */
> tmp = b->in[b->in_pos++];
>
> + if (tmp == 0x00)
> + return XZ_STREAM_END;
> +
> if (tmp >= 0xE0 || tmp == 0x01) {
> s->lzma2.need_props = true;
> s->lzma2.need_dict_reset = false;
> @@ -1001,9 +1004,6 @@ XZ_EXTERN enum xz_ret xz_dec_lzma2_run(s
> lzma_reset(s);
> }
> } else {
> - if (tmp == 0x00)
> - return XZ_STREAM_END;
> -
> if (tmp > 0x02)
> return XZ_DATA_ERROR;
>