Use putenv to implement unsetenv/clearenv

noexec applets failed on ReactOS 0.3.17.  This was because the
environment was being manipulated directly using the environ pointer.
Implementing unsetenv and clearenv using putenv fixes the problem.

WIN32 putenv doesn't allow environment variables to have empty
values.  This was the case before and it's still the case after
this change.  Shell variables are fine.

2 files changed, 49 insertions, 12 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 7caedd063..654ca3ee6 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -180,13 +180,15 @@ int mingw_system(const char *cmd);
 
 int clearenv(void);
 char *mingw_getenv(const char *name);
+int mingw_putenv(const char *env);
 char *mingw_mktemp(char *template);
 int mkstemp(char *template);
 char *realpath(const char *path, char *resolved_path);
 int setenv(const char *name, const char *value, int replace);
-void unsetenv(const char *env);
+int unsetenv(const char *env);
 
 #define getenv mingw_getenv
+#define putenv mingw_putenv
 #define mktemp mingw_mktemp
 
 /*
diff --git a/win32/env.c b/win32/env.c
index f8d231a8f..eb2e1f004 100644
--- a/win32/env.c
+++ b/win32/env.c
@@ -104,27 +104,62 @@ char **env_setenv(char **env, const char *name)
                 else {
                         for (; env[i]; i++)
                                 env[i] = env[i+1];
-                        SetEnvironmentVariable(name, NULL);
                 }
         }
         return env;
 }
 
-void unsetenv(const char *env)
+/*
+ * Removing an environment variable with WIN32 putenv requires an argument
+ * like "NAME="; glibc omits the '='.  The implementations of unsetenv and
+ * clearenv allow for this.
+ *
+ * It isn't possible to create an environment variable with an empty value
+ * using WIN32 putenv.
+ */
+#undef putenv
+int unsetenv(const char *env)
 {
-        env_setenv(environ, env);
+        char *name;
+        int ret;
+
+        name = xmalloc(strlen(env)+2);
+        strcat(strcpy(name, env), "=");
+        ret = putenv(name);
+        free(name);
+
+        return ret;
 }
 
 int clearenv(void)
 {
-        char **env = environ;
-        if (!env)
-                return 0;
-        while (*env) {
-                free(*env);
-                env++;
+        char *name, *s;
+
+        while ( environ && *environ ) {
+                if ( (s=strchr(*environ, '=')) != NULL ) {
+                        name = xstrndup(*environ, s-*environ+1);
+                        putenv(name);
+                        free(name);
+                }
+                else {
+                        return -1;
+                }
         }
-        free(env);
-        environ = NULL;
+        return 0;
+}
+
+int mingw_putenv(const char *env)
+{
+        char *s;
+
+        if ( (s=strchr(env, '=')) == NULL ) {
+                return unsetenv(env);
+        }
+
+        if ( s[1] != '\0' ) {
+                return putenv(env);
+        }
+
+        /* can't set empty value */
         return 0;
 }