Replace the libc environment with a thread-safe emulation

putenv(3) and friends aren't thread-safe regardless of how you slice
it; a global lock around all environment operations (like before)
keeps things safe as far as our own operations go, but we have
absolutely no control over what libc or a library dragged in by a
driver/NIF does -- they're free to call getenv(3) or putenv(3)
without honoring our lock.

This commit solves this by setting up an "emulated" environment which
can't be touched without going through our interfaces. Third-party
libraries can still shoot themselves in the foot but benign uses of
os:putenv/2 will no longer risk crashing the emulator.

1 files changed, 212 insertions, 319 deletions

diff --git a/erts/emulator/sys/win32/sys_env.c b/erts/emulator/sys/win32/sys_env.c
index 5792816267..c78161b344 100644
--- a/erts/emulator/sys/win32/sys_env.c
+++ b/erts/emulator/sys/win32/sys_env.c
@@ -1,319 +1,212 @@
-/*

- * %CopyrightBegin%

- *

- * Copyright Ericsson AB 2002-2016. All Rights Reserved.

- *

- * Licensed under the Apache License, Version 2.0 (the "License");

- * you may not use this file except in compliance with the License.

- * You may obtain a copy of the License at

- *

- *     http://www.apache.org/licenses/LICENSE-2.0

- *

- * Unless required by applicable law or agreed to in writing, software

- * distributed under the License is distributed on an "AS IS" BASIS,

- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

- * See the License for the specific language governing permissions and

- * limitations under the License.

- *

- * %CopyrightEnd%

- */

-

-#ifdef HAVE_CONFIG_H

-#  include "config.h"

-#endif

-

-#include "sys.h"

-#include "erl_sys_driver.h"

-#include "erl_alloc.h"

-

-static WCHAR *merge_environment(WCHAR *current, WCHAR *add);

-static WCHAR *arg_to_env(WCHAR **arg);

-static WCHAR **env_to_arg(WCHAR *env);

-static WCHAR **find_arg(WCHAR **arg, WCHAR *str);

-static int compare(const void *a, const void *b);

-

-static erts_rwmtx_t environ_rwmtx;
-

-void

-erts_sys_env_init(void)

-{

-    erts_rwmtx_init(&environ_rwmtx, "environ", NIL,
-        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_GENERIC);

-}

-

-int

-erts_sys_putenv_raw(char *key, char *value)

-{

-    int res;

-    erts_rwmtx_rwlock(&environ_rwmtx);
-    res = (SetEnvironmentVariable((LPCTSTR) key,

-				  (LPCTSTR) value) ? 0 : 1);

-    erts_rwmtx_rwunlock(&environ_rwmtx);
-    return res;

-}

-

-int

-erts_sys_putenv(char *key, char *value)

-{

-    int res;

-    WCHAR *wkey = (WCHAR *) key;

-    WCHAR *wvalue = (WCHAR *) value;

-    erts_rwmtx_rwlock(&environ_rwmtx);
-    res = (SetEnvironmentVariableW(wkey,

-				   wvalue) ? 0 : 1);

-    erts_rwmtx_rwunlock(&environ_rwmtx);
-    return res;

-}

-

-int

-erts_sys_getenv(char *key, char *value, size_t *size)

-{

-    size_t req_size = 0;

-    int res = 0;

-    DWORD new_size;

-    WCHAR *wkey = (WCHAR *) key;

-    WCHAR *wvalue = (WCHAR *) value;

-    DWORD wsize = *size / (sizeof(WCHAR) / sizeof(char));

-

-    SetLastError(0);

-    erts_rwmtx_rlock(&environ_rwmtx);
-    new_size = GetEnvironmentVariableW(wkey,

-				       wvalue,

-				      (DWORD) wsize);

-    res = !new_size && GetLastError() == ERROR_ENVVAR_NOT_FOUND ? -1 : 0;

-    erts_rwmtx_runlock(&environ_rwmtx);
-    if (res < 0)

-	return res;

-    res = new_size > wsize ? 1 : 0;

-    *size = new_size * (sizeof(WCHAR) / sizeof(char));

-    return res;

-}

-int

-erts_sys_getenv__(char *key, char *value, size_t *size)

-{

-    size_t req_size = 0;

-    int res = 0;

-    DWORD new_size;

-

-    SetLastError(0);

-    new_size = GetEnvironmentVariable((LPCTSTR) key,

-				      (LPTSTR) value,

-				      (DWORD) *size);

-    res = !new_size && GetLastError() == ERROR_ENVVAR_NOT_FOUND ? -1 : 0;

-    if (res < 0)

-	return res;

-    res = new_size > *size ? 1 : 0;

-    *size = new_size;

-    return res;

-}

-

-int

-erts_sys_getenv_raw(char *key, char *value, size_t *size)

-{

-    int res;

-    erts_rwmtx_rlock(&environ_rwmtx);
-    res = erts_sys_getenv__(key, value, size);

-    erts_rwmtx_runlock(&environ_rwmtx);
-    return res;

-}

-

-void init_getenv_state(GETENV_STATE *state)

-{

-    erts_rwmtx_rlock(&environ_rwmtx);
-    state->environment_strings = GetEnvironmentStringsW();

-    state->next_string = state->environment_strings;

-}

-

-char *getenv_string(GETENV_STATE *state)

-{

-    ERTS_LC_ASSERT(erts_lc_rwmtx_is_rlocked(&environ_rwmtx));
-    if (state->next_string[0] == L'\0') {

-	return NULL;

-    } else {

-	WCHAR *res = state->next_string;

-	state->next_string += wcslen(res) + 1;

-	return (char *) res;

-    }

-}

-

-void fini_getenv_state(GETENV_STATE *state)

-{

-    FreeEnvironmentStringsW(state->environment_strings);

-    state->environment_strings = state->next_string = NULL;

-    erts_rwmtx_runlock(&environ_rwmtx);
-}

-

-int erts_sys_unsetenv(char *key)

-{

-    int res = 0;

-    WCHAR *wkey = (WCHAR *) key;

-

-    SetLastError(0);

-    erts_rwmtx_rlock(&environ_rwmtx);
-    GetEnvironmentVariableW(wkey,

-                            NULL,

-                            0);

-    if (GetLastError() != ERROR_ENVVAR_NOT_FOUND) {

-        res = (SetEnvironmentVariableW(wkey,

-                                       NULL) ? 0 : 1);

-    }

-    erts_rwmtx_runlock(&environ_rwmtx);
-    return res;

-}

-

-char*

-win_build_environment(char* new_env)

-{

-    if (new_env == NULL) {

-	return NULL;

-    } else {

-	WCHAR *tmp, *merged, *tmp_new;

-

-	tmp_new = (WCHAR *) new_env;

-	

-	erts_rwmtx_rlock(&environ_rwmtx);
-	tmp = GetEnvironmentStringsW();

-	merged = merge_environment(tmp, tmp_new);

-

-	FreeEnvironmentStringsW(tmp);

-	erts_rwmtx_runlock(&environ_rwmtx);
-	return (char *) merged;

-    }

-}

-

-static WCHAR *

-merge_environment(WCHAR *old, WCHAR *add)

-{

-    WCHAR **a_arg = env_to_arg(add);

-    WCHAR **c_arg = env_to_arg(old);

-    WCHAR *ret;

-    int i, j;

-    

-    for(i = 0; c_arg[i] != NULL; ++i)

-	;

-

-    for(j = 0; a_arg[j] != NULL; ++j)

-	;

-

-    c_arg = erts_realloc(ERTS_ALC_T_TMP,

-			 c_arg, (i+j+1) * sizeof(WCHAR *));

-

-    for(j = 0; a_arg[j] != NULL; ++j){

-	WCHAR **tmp;

-	WCHAR *current = a_arg[j];

-	WCHAR *eq_p = wcschr(current,L'=');

-	int unset = (eq_p!=NULL && eq_p[1]==L'\0');

-

-	if ((tmp = find_arg(c_arg, current)) != NULL) {

-	    if (!unset) {

-		*tmp = current;

-	    } else {

-		*tmp = c_arg[--i];

-		c_arg[i] = NULL;

-	    }

-	} else if (!unset) {

-	    c_arg[i++] = current;

-	    c_arg[i] = NULL;

-	}

-    }

-    ret = arg_to_env(c_arg);

-    erts_free(ERTS_ALC_T_TMP, c_arg);

-    erts_free(ERTS_ALC_T_TMP, a_arg);

-    return ret;

-}

-

-static WCHAR**

-find_arg(WCHAR **arg, WCHAR *str)

-{

-    WCHAR *tmp;

-    int len;

-

-    if ((tmp = wcschr(str, L'=')) != NULL) {

-	tmp++;

-	len = tmp - str;

-	while (*arg != NULL){

-	    if (_wcsnicmp(*arg, str, len) == 0){

-		return arg;

-	    }

-	    ++arg;

-	}

-    }

-    return NULL;

-}

-

-static int

-compare(const void *a, const void *b)

-{

-    WCHAR *s1 = *((WCHAR **) a);

-    WCHAR *s2 = *((WCHAR **) b);

-    WCHAR *e1 = wcschr(s1,L'=');

-    WCHAR *e2 = wcschr(s2,L'=');

-    int ret;

-    int len;

-  

-    if(!e1)

-	e1 = s1 + wcslen(s1);

-    if(!e2)

-	e2 = s2 + wcslen(s2);

-  

-    if((e1 - s1) > (e2 - s2))

-	len = (e2 - s2);

-    else

-	len = (e1 - s1);

-  

-    ret = _wcsnicmp(s1,s2,len);

-    if (ret == 0)

-	return ((e1 - s1) - (e2 - s2));

-    else

-	return ret;

-}

-

-static WCHAR**

-env_to_arg(WCHAR *env)

-{

-    WCHAR **ret;

-    WCHAR *tmp;

-    int i;

-    int num_strings = 0;

-

-    for(tmp = env; *tmp != '\0'; tmp += wcslen(tmp)+1) {

-	++num_strings;

-    }

-    ret = erts_alloc(ERTS_ALC_T_TMP, sizeof(WCHAR *) * (num_strings + 1));

-    i = 0;

-    for(tmp = env; *tmp != '\0'; tmp += wcslen(tmp)+1){

-	ret[i++] = tmp;

-    }

-    ret[i] = NULL;

-    return ret;

-}

-

-static WCHAR *

-arg_to_env(WCHAR **arg)

-{

-    WCHAR *block;

-    WCHAR *ptr;

-    int i;

-    int totlen = 1;		/* extra '\0' */

-

-    for(i = 0; arg[i] != NULL; ++i) {

-	totlen += wcslen(arg[i])+1;

-    }

-

-    /* sort the environment vector */

-    qsort(arg, i, sizeof(WCHAR *), &compare);

-

-    if (totlen == 1){

-	block = erts_alloc(ERTS_ALC_T_ENVIRONMENT, 2 * sizeof(WCHAR));

-	block[0] = block[1] = '\0'; 

-    } else {

-	block = erts_alloc(ERTS_ALC_T_ENVIRONMENT, totlen * sizeof(WCHAR));

-	ptr = block;

-	for(i=0; arg[i] != NULL; ++i){

-	    wcscpy(ptr, arg[i]);

-	    ptr += wcslen(ptr)+1;

-	}

-	*ptr = '\0';

-    }

-    return block;

-}

+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 2002-2017. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include "sys.h"
+#include "erl_sys_driver.h"
+#include "erl_alloc.h"
+
+static erts_osenv_t sysenv_global_env;
+static erts_rwmtx_t sysenv_rwmtx;
+
+static void import_initial_env(void);
+
+void erts_sys_env_init() {
+    erts_rwmtx_init(&sysenv_rwmtx, "environ", NIL,
+        ERTS_LOCK_FLAGS_PROPERTY_STATIC | ERTS_LOCK_FLAGS_CATEGORY_GENERIC);
+
+    erts_osenv_init(&sysenv_global_env);
+    import_initial_env();
+}
+
+const erts_osenv_t *erts_sys_rlock_global_osenv() {
+    erts_rwmtx_rlock(&sysenv_rwmtx);
+    return &sysenv_global_env;
+}
+
+erts_osenv_t *erts_sys_rwlock_global_osenv() {
+    erts_rwmtx_rwlock(&sysenv_rwmtx);
+    return &sysenv_global_env;
+}
+
+void erts_sys_runlock_global_osenv() {
+    erts_rwmtx_runlock(&sysenv_rwmtx);
+}
+
+void erts_sys_rwunlock_global_osenv() {
+    erts_rwmtx_rwunlock(&sysenv_rwmtx);
+}
+
+int erts_sys_explicit_host_getenv(char *key, char *value, size_t *size) {
+    size_t new_size = GetEnvironmentVariableA(key, value, (DWORD)*size);
+
+    if(new_size == 0 && GetLastError() == ERROR_ENVVAR_NOT_FOUND) {
+        return 0;
+    } else if(new_size > *size) {
+        return -1;
+    }
+
+    *size = new_size;
+    return 1;
+}
+
+int erts_sys_explicit_8bit_putenv(char *key, char *value) {
+    WCHAR *wide_key, *wide_value;
+    int key_length, value_length;
+    int result;
+
+    /* Note that we do *NOT* honor the filename encoding flags (+fnu/+fnl)
+     * here; the previous implementation used SetEnvironmentVariableA and
+     * things may break if we step away from that. */
+
+    key_length = MultiByteToWideChar(CP_ACP, 0, key, -1, NULL, 0);
+    value_length = MultiByteToWideChar(CP_ACP, 0, value, -1, NULL, 0);
+
+    /* Report "not found" if either string isn't convertible. */
+    if(key_length == 0 || value_length == 0) {
+        return 0;
+    }
+
+    wide_key = erts_alloc(ERTS_ALC_T_TMP, key_length * sizeof(WCHAR));
+    wide_value = erts_alloc(ERTS_ALC_T_TMP, value_length * sizeof(WCHAR));
+
+    MultiByteToWideChar(CP_ACP, 0, key, -1, wide_key, key_length);
+    MultiByteToWideChar(CP_ACP, 0, value, -1, wide_value, value_length);
+
+    {
+        erts_osenv_data_t env_key, env_value;
+        erts_osenv_t *env;
+
+        env = erts_sys_rwlock_global_osenv();
+
+        /* -1 to exclude the NUL terminator. */
+        env_key.length = (key_length - 1) * sizeof(WCHAR);
+        env_key.data = wide_key;
+
+        env_value.length = (value_length - 1) * sizeof(WCHAR);
+        env_value.data = wide_value;
+
+        result = erts_osenv_put_native(env, &env_key, &env_value);
+        erts_sys_rwunlock_global_osenv();
+    }
+
+    erts_free(ERTS_ALC_T_TMP, wide_key);
+    erts_free(ERTS_ALC_T_TMP, wide_value);
+
+    return result;
+}
+
+int erts_sys_explicit_8bit_getenv(char *key, char *value, size_t *size) {
+    erts_osenv_data_t env_key, env_value;
+    int key_length, value_length, result;
+    WCHAR *wide_key, *wide_value;
+
+    key_length = MultiByteToWideChar(CP_ACP, 0, key, -1, NULL, 0);
+
+    /* Report "not found" if the string isn't convertible. */
+    if(key_length == 0) {
+        return 0;
+    }
+
+    wide_key = erts_alloc(ERTS_ALC_T_TMP, key_length * sizeof(WCHAR));
+    MultiByteToWideChar(CP_ACP, 0, key, -1, wide_key, key_length);
+
+    /* We assume that the worst possible size is twice the output buffer width,
+     * as we could theoretically be on a code page that requires surrogates. */
+    value_length = (*size) * 2;
+    wide_value = erts_alloc(ERTS_ALC_T_TMP, value_length * sizeof(WCHAR));
+
+    {
+        const erts_osenv_t *env = erts_sys_rlock_global_osenv();
+
+        /* -1 to exclude the NUL terminator. */
+        env_key.length = (key_length - 1) * sizeof(WCHAR);
+        env_key.data = wide_key;
+
+        env_value.length = value_length * sizeof(WCHAR);
+        env_value.data = wide_value;
+
+        result = erts_osenv_get_native(env, &env_key, &env_value);
+        erts_sys_runlock_global_osenv();
+    }
+
+    if(result == 1 && env_value.length > 0) {
+        /* This function doesn't NUL-terminate if the provided size is >= 0,
+         * so we pass (*size - 1) to reserve space for it and then do it
+         * manually. */
+        *size = WideCharToMultiByte(CP_ACP, 0, env_value.data,
+            env_value.length / sizeof(WCHAR), value, *size - 1, NULL, NULL);
+
+        if(*size == 0) {
+            if(GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
+                result = -1;
+            } else {
+                result = 0;
+            }
+        }
+    } else {
+        *size = 0;
+    }
+
+    if(*size > 0) {
+        value[*size] = '\0';
+    }
+
+    erts_free(ERTS_ALC_T_TMP, wide_key);
+    erts_free(ERTS_ALC_T_TMP, wide_value);
+
+    return result;
+}
+
+static void import_initial_env(void) {
+    WCHAR *environment_block, *current_variable;
+
+    environment_block = GetEnvironmentStringsW();
+    current_variable = environment_block;
+
+    while(wcslen(current_variable) > 0) {
+        WCHAR *separator_index = wcschr(current_variable, L'=');
+
+        /* We tolerate environment variables starting with '=' as the per-drive
+         * working directories are stored this way. */
+        if(separator_index == current_variable) {
+            separator_index = wcschr(separator_index + 1, L'=');
+        }
+
+        if(separator_index != NULL && separator_index != current_variable) {
+            erts_osenv_data_t env_key, env_value;
+
+            env_key.length = (separator_index - current_variable) * sizeof(WCHAR);
+            env_key.data = current_variable;
+
+            env_value.length = (wcslen(separator_index) - 1) * sizeof(WCHAR);
+            env_value.data = separator_index + 1;
+
+            erts_osenv_put_native(&sysenv_global_env, &env_key, &env_value);
+        }
+
+        current_variable += wcslen(current_variable) + 1;
+    }
+
+    FreeEnvironmentStringsW(environment_block);
+}