win32: implement symlink(2)

Provide an implementation of symlink(2).

Calls to symlink(2) will fail in default Windows installations unless
running with elevated privileges.  Failure to create a symlink when
extracting files from an archive is therefore treated as a non-fatal
error.

There are two ways to permit the creation of symlinks:

- Edit security policy to give users the 'Create symbolic links'
  privilege.  Unfortunately this doesn't work for users who are an
  Administrator.

- Enable developer mode, which is available in later versions of
  Windows 10.

The ability to create symlinks is not available in Windows XP
or ReactOS.

1 files changed, 19 insertions, 11 deletions

diff --git a/archival/libarchive/unsafe_symlink_target.c b/archival/libarchive/unsafe_symlink_target.c
index b5f5a2670..8e4cd4380 100644
--- a/archival/libarchive/unsafe_symlink_target.c
+++ b/archival/libarchive/unsafe_symlink_target.c
@@ -5,12 +5,17 @@
 #include "libbb.h"
 #include "bb_archive.h"
 
+/* symlink may not be available for WIN32, just issue a warning */
+#if ENABLE_PLATFORM_MINGW32
+# undef bb_perror_msg_and_die
+# define bb_perror_msg_and_die(...) bb_perror_msg(__VA_ARGS__)
+#endif
+
 void FAST_FUNC create_or_remember_link(llist_t **link_placeholders,
                 const char *target,
                 const char *linkname,
                 int hard_link)
 {
-#if !ENABLE_PLATFORM_MINGW32
         if (hard_link || target[0] == '/' || strstr(target, "..")) {
                 llist_add_to_end(link_placeholders,
                         xasprintf("%c%s%c%s", hard_link, linkname, '\0', target)
@@ -23,16 +28,6 @@ void FAST_FUNC create_or_remember_link(llist_t **link_placeholders,
                         "sym", linkname, target
                 );
         }
-#else
-        if (hard_link) {
-                llist_add_to_end(link_placeholders,
-                        xasprintf("%c%s%c%s", hard_link, linkname, '\0', target)
-                );
-                return;
-        }
-        /* symlink isn't implemented for WIN32, just issue a warning */
-        bb_perror_msg("can't create symlink '%s' to '%s'", linkname, target);
-#endif
 }
 
 void FAST_FUNC create_links_from_list(llist_t *list)
@@ -42,11 +37,24 @@ void FAST_FUNC create_links_from_list(llist_t *list)
 
                 target = list->data + 1 + strlen(list->data + 1) + 1;
                 if ((*list->data ? link : symlink) (target, list->data + 1)) {
+#if !ENABLE_PLATFORM_MINGW32
                         /* shared message */
                         bb_error_msg_and_die("can't create %slink '%s' to '%s'",
                                 *list->data ? "hard" : "sym",
                                 list->data + 1, target
                         );
+#else
+                        if (!*list->data)
+                                bb_error_msg("can't create %slink '%s' to '%s'",
+                                        "sym",
+                                        list->data + 1, target
+                                );
+                        else
+                                bb_error_msg_and_die("can't create %slink '%s' to '%s'",
+                                        "hard",
+                                        list->data + 1, target
+                                );
+#endif
                 }
                 list = list->link;
         }