win32: retry when command needs elevated privileges

Some installer programs have an entry in their manifest to indicate
that they need elevated privileges.  The shell in busybox-w32 was
unable to run such programs.

When a program fails to run with ERROR_ELEVATION_REQUIRED, try
again using ShellExecuteEx() with the 'runas' verb to give it
elevated privileges.

Adds 272-288 bytes.

(GitHub issue #481)

4 files changed, 71 insertions, 12 deletions

diff --git a/include/mingw.h b/include/mingw.h
index c41c0f91e..3ee1cc46f 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -669,3 +669,4 @@ enum {
 };
 int elevation_state(void);
 void set_interp(int i) FAST_FUNC;
+int mingw_shell_execute(SHELLEXECUTEINFO *info);
diff --git a/loginutils/suw32.c b/loginutils/suw32.c
index b3976dcfd..77c038582 100644
--- a/loginutils/suw32.c
+++ b/loginutils/suw32.c
@@ -48,8 +48,8 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         char *opt_command = NULL;
         char *opt_shell = NULL;
         SHELLEXECUTEINFO info;
-        char *bb_path, *cwd, *realcwd, *q, *args;
-        DECLARE_PROC_ADDR(BOOL, ShellExecuteExA, SHELLEXECUTEINFOA *);
+        const char *bb_path;
+        char *cwd, *realcwd, *q, *args;
 
         opt = getopt32(argv, "^c:s:tNW" "\0" "s--N:N--s", &opt_command, &opt_shell);
         argv += optind;
@@ -70,19 +70,17 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         }
 #endif
 
-        /* ShellExecuteEx() needs backslash as separator in UNC paths. */
         if (opt_shell) {
                 bb_path = file_is_win32_exe(opt_shell);
                 if (!bb_path)
                         bb_error_msg_and_die("%s: Not found", opt_shell);
                 args = NULL;
         } else {
-                bb_path = xstrdup(bb_busybox_exec_path);
+                bb_path = bb_busybox_exec_path;
                 args = xstrdup("--busybox ash");
                 if (!test_mode)
                         args = xappendword(args, "-t \"BusyBox ash (Admin)\"");
         }
-        slash_to_bs(bb_path);
 
         memset(&info, 0, sizeof(SHELLEXECUTEINFO));
         info.cbSize = sizeof(SHELLEXECUTEINFO);
@@ -137,12 +135,7 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         /* info.lpDirectory = NULL; */
         info.nShow = SW_SHOWNORMAL;
 
-        if (!INIT_PROC_ADDR(shell32.dll, ShellExecuteExA)) {
-                ret = -1;
-                goto end;
-        }
-
-        if (!ShellExecuteExA(&info)) {
+        if (!mingw_shell_execute(&info)) {
                 ret = 1;
                 goto end;
         }
@@ -159,7 +152,8 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         }
  end:
         if (ENABLE_FEATURE_CLEAN_UP) {
-                free(bb_path);
+                if (bb_path != bb_busybox_exec_path)
+                        free((void *)bb_path);
                 free(cwd);
                 free(realcwd);
                 free(args);
diff --git a/win32/mingw.c b/win32/mingw.c
index 7a5198ccf..cb1f84f30 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -2538,3 +2538,25 @@ char * FAST_FUNC exe_relative_path(const char *tail)
         free(exepath);
         return relpath;
 }
+
+int mingw_shell_execute(SHELLEXECUTEINFO *info)
+{
+        DECLARE_PROC_ADDR(BOOL, ShellExecuteExA, SHELLEXECUTEINFOA *);
+        char *lpath;
+        int ret;
+
+        if (!INIT_PROC_ADDR(shell32.dll, ShellExecuteExA)) {
+                errno = ENOSYS;
+                return FALSE;
+        }
+
+        // ShellExecuteEx() needs backslash as separator in UNC paths.
+        lpath = xstrdup(info->lpFile);
+        slash_to_bs(lpath);
+        info->lpFile = lpath;
+
+        ret = ShellExecuteExA(info);
+
+        free(lpath);
+        return ret;
+}
diff --git a/win32/process.c b/win32/process.c
index fd89707ca..33f45ee42 100644
--- a/win32/process.c
+++ b/win32/process.c
@@ -501,6 +501,38 @@ static NORETURN void wait_for_child(HANDLE child, const char *cmd)
         exit((int)code);
 }
 
+static intptr_t
+shell_execute(const char *path, char *const *argv)
+{
+        SHELLEXECUTEINFO info;
+        char *args;
+
+        memset(&info, 0, sizeof(SHELLEXECUTEINFO));
+        info.cbSize = sizeof(SHELLEXECUTEINFO);
+        info.fMask = SEE_MASK_NOCLOSEPROCESS;
+        /* info.hwnd = NULL; */
+        info.lpVerb = "runas";
+        info.lpFile = path;
+
+        args = NULL;
+        if (*argv++) {
+                while (*argv) {
+                        char *q = quote_arg(*argv++);
+                        args = xappendword(args, q);
+                        free(q);
+                }
+        }
+
+        info.lpParameters = args;
+        /* info.lpDirectory = NULL; */
+        info.nShow = SW_SHOWNORMAL;
+
+        mingw_shell_execute(&info);
+
+        free(args);
+        return info.hProcess ? (intptr_t)info.hProcess : -1;
+}
+
 int
 mingw_execvp(const char *cmd, char *const *argv)
 {
@@ -514,6 +546,16 @@ int
 mingw_execve(const char *cmd, char *const *argv, char *const *envp)
 {
         intptr_t ret = mingw_spawn_interpreter(P_NOWAIT, cmd, argv, envp, 0);
+
+        if (ret == -1 && GetLastError() == ERROR_ELEVATION_REQUIRED) {
+                // Command exists but failed because it wants elevated privileges.
+                // Try again using ShellExecuteEx().
+                SetLastError(0);
+                ret = shell_execute(cmd, argv);
+                if (GetLastError())
+                        exit(1);
+        }
+
         if (ret != -1)
                 wait_for_child((HANDLE)ret, cmd);
         return ret;