linux-kernel - [PATCH] XZ decompressor: Fix decoding of empty LZMA2 streams

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Message-Id: <201105011938.42851.lasse.collin@tukaani.org>
Date:	Sun, 1 May 2011 19:38:42 +0300
From:	Lasse Collin <lasse.collin@...aani.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] XZ decompressor: Fix decoding of empty LZMA2 streams

From: Lasse Collin <lasse.collin@...aani.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@...aani.org>
---

 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;
 
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