[Xen-devel] [PATCH] XZ decompressor: Fix decoding of empty LZMA2 streams

["Jan Beulich" <JBeulich@xxxxxxxx>]

From: Lasse Collin <lasse.collin@xxxxxxxxxxx>

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@xxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/xz/dec_lzma2.c
+++ b/xen/common/xz/dec_lzma2.c
@@ -969,6 +969,9 @@ XZ_EXTERN enum xz_ret INIT xz_dec_lzma2_
                         */
                        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 INIT xz_dec_lzma2_
                                                lzma_reset(s);
                                }
                        } else {
-                               if (tmp == 0x00)
-                                       return XZ_STREAM_END;
-
                                if (tmp > 0x02)
                                        return XZ_DATA_ERROR;

Attachment: xz-decode-empty.patch
Description: Text document

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