From 1847ec67cec36a17354115374954fea211d1f0da Mon Sep 17 00:00:00 2001
From: Sergey Poznyakoff <gray@gnu.org.ua>
Date: Thu, 19 Feb 2015 17:00:58 +0200
Subject: [PATCH] Improve compression format recognition

Some comressed archives can pass the checksum test, which makes tar
treat them as uncompressed archives.

* src/buffer.c (check_compressed_archive): Test the checksum only
if the block we read looks like a valid tar header (i.e. has
a magic string).
---
 src/buffer.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/buffer.c b/src/buffer.c
index a7d8971..1a96595 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -391,7 +391,10 @@ check_compressed_archive (bool *pshort)
   /* Restore global values */
   read_full_records = sfr;
 
-  if (tar_checksum (record_start, true) == HEADER_SUCCESS)
+  if ((strcmp (record_start->header.magic, TMAGIC) == 0 ||
+       strcmp (record_start->buffer + offsetof (struct posix_header, magic),
+	       OLDGNU_MAGIC) == 0) &&
+      tar_checksum (record_start, true) == HEADER_SUCCESS)
     /* Probably a valid header */
     return ct_tar;
 
-- 
2.13.5



From 1e8b786e651d174a5fc9bf63a08d00c2d592ee3e Mon Sep 17 00:00:00 2001
From: Pavel Raiskup <praiskup@redhat.com>
Date: Thu, 30 Mar 2017 13:30:15 +0200
Subject: [PATCH] Fix non-deterministic archive type detection

Due to analysis of partly uninitialized read-ahead buffer
(short_read call), we sometimes mistakenly classified very small
compressed archives as non-compressed; which in turn caused
extraction failure.

* src/buffer.c (check_compressed_archive): Don't assume that
archives smaller than BLOCKSIZE could be non-compressed, as tar
header always has at least one block.
---
 src/buffer.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/buffer.c b/src/buffer.c
index 57fe813..6f96c2f 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -402,10 +402,12 @@ check_compressed_archive (bool *pshort)
   /* Restore global values */
   read_full_records = sfr;
 
-  if ((strcmp (record_start->header.magic, TMAGIC) == 0 ||
-       strcmp (record_start->buffer + offsetof (struct posix_header, magic),
-	       OLDGNU_MAGIC) == 0) &&
-      tar_checksum (record_start, true) == HEADER_SUCCESS)
+  if (record_start != record_end /* no files smaller than BLOCKSIZE */
+      && (strcmp (record_start->header.magic, TMAGIC) == 0
+          || strcmp (record_start->buffer + offsetof (struct posix_header,
+                                                      magic),
+                     OLDGNU_MAGIC) == 0)
+      && tar_checksum (record_start, true) == HEADER_SUCCESS)
     /* Probably a valid header */
     return ct_tar;
 
-- 
2.13.5