dpkg-deb: work around bogus error message when working with XZ compressed packages

function                                             old     new   delta
unpack_xz_stream                                    2309    2317      +8
bb_full_fd_action                                    464     472      +8

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 20 insertions, 2 deletions

diff --git a/archival/libarchive/decompress_unxz.c b/archival/libarchive/decompress_unxz.c
index 8ae7a275b..948ef978c 100644
--- a/archival/libarchive/decompress_unxz.c
+++ b/archival/libarchive/decompress_unxz.c
@@ -96,6 +96,24 @@ unpack_xz_stream(transformer_state_t *xstate)
                          */
                         do {
                                 if (membuf[iobuf.in_pos] != 0) {
+                                        /* There is more data, but is it XZ data?
+                                         * Example: dpkg-deb -f busybox_1.30.1-4_amd64.deb
+                                         * reads control.tar.xz "control" file
+                                         * inside the ar archive, but tar.xz
+                                         * extraction code reaches end of xz data,
+                                         * reached this code and reads the beginning
+                                         * of data.tar.xz's ar header, which isn't xz data,
+                                         * and prints "corrupted data".
+                                         * The correct solution is to not read
+                                         * past nested archive (to simulate EOF).
+                                         * This is a workaround:
+                                         */
+                                        if (membuf[iobuf.in_pos] != 0xfd) {
+                                                /* It's definitely not a xz signature
+                                                 * (which is 0xfd,"7zXZ",0x00).
+                                                 */
+                                                goto end;
+                                        }
                                         xz_dec_reset(state);
                                         goto do_run;
                                 }
@@ -128,7 +146,7 @@ unpack_xz_stream(transformer_state_t *xstate)
                         break;
                 }
         }
-
+ end:
         xz_dec_end(state);
         free(membuf);
 
diff --git a/archival/libarchive/unxz/xz_stream.h b/archival/libarchive/unxz/xz_stream.h
index 66cb5a705..45056e42c 100644
--- a/archival/libarchive/unxz/xz_stream.h
+++ b/archival/libarchive/unxz/xz_stream.h
@@ -25,7 +25,7 @@
 
 #define STREAM_HEADER_SIZE 12
 
-#define HEADER_MAGIC "\3757zXZ"
+#define HEADER_MAGIC "\375""7zXZ"
 #define HEADER_MAGIC_SIZE 6
 
 #define FOOTER_MAGIC "YZ"