tar: on extract, everything up to and including last ".." is stripped

function                                             old     new   delta
get_header_tar                                      1493    1545     +52

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

3 files changed, 41 insertions, 5 deletions

diff --git a/archival/libarchive/get_header_tar.c b/archival/libarchive/get_header_tar.c
index 2e0332792..6a1532c86 100644
--- a/archival/libarchive/get_header_tar.c
+++ b/archival/libarchive/get_header_tar.c
@@ -422,11 +422,28 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
                 p_linkname = NULL;
         }
 #endif
-        if (strncmp(file_header->name, "/../"+1, 3) == 0
-         || strstr(file_header->name, "/../")
-        ) {
-                bb_error_msg_and_die("name with '..' encountered: '%s'",
-                                file_header->name);
+
+        /* Everything up to and including last ".." component is stripped */
+        cp = file_header->name;
+        while (1) {
+                char *cp2;
+                if (strncmp(cp, "/../"+1, 3) == 0) {
+                        cp += 3;
+                        continue;
+                }
+                cp2 = strstr(cp, "/../");
+                if (cp2) {
+                        cp = cp2 + 4;
+                        continue;
+                }
+                break;
+        }
+        if (cp != file_header->name) {
+                if (!(archive_handle->ah_flags & ARCHIVE_TAR__TRUNC_WARNED)) {
+                        archive_handle->ah_flags |= ARCHIVE_TAR__TRUNC_WARNED;
+                        bb_error_msg("removing leading '%.*s'", (int)(cp - file_header->name), file_header->name);
+                }
+                overlapping_strcpy(file_header->name, cp);
         }
 
         /* Strip trailing '/' in directories */
diff --git a/include/archive.h b/include/archive.h
index 49c478728..9fc77e542 100644
--- a/include/archive.h
+++ b/include/archive.h
@@ -118,6 +118,8 @@ typedef struct archive_handle_t {
 #define ARCHIVE_DONT_RESTORE_PERM   (1 << 6)
 #define ARCHIVE_NUMERIC_OWNER       (1 << 7)
 #define ARCHIVE_O_TRUNC             (1 << 8)
+/* Archiver specific. */
+#define ARCHIVE_TAR__TRUNC_WARNED   (1 << 9)
 
 
 /* POSIX tar Header Block, from POSIX 1003.1-1990  */
diff --git a/testsuite/tar.tests b/testsuite/tar.tests
index 472064f7f..d41d10d57 100755
--- a/testsuite/tar.tests
+++ b/testsuite/tar.tests
@@ -168,6 +168,23 @@ Ok
 " \
 "" ""
 
+# On extract, everything up to and including last ".." component is stripped
+testing "tar strips /../ on extract" "\
+rm -rf input_* test.tar 2>/dev/null
+mkdir input_dir
+echo Ok >input_dir/file
+tar cf test.tar ./../tar.tempdir/input_dir/../input_dir 2>&1
+rm -rf input_* 2>/dev/null
+tar -vxf test.tar 2>&1
+cat input_dir/file 2>&1
+" "\
+tar: removing leading './../tar.tempdir/input_dir/../'
+input_dir/
+input_dir/file
+Ok
+" \
+"" ""
+
 
 cd .. && rm -rf tar.tempdir || exit 1