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.

3 files changed, 157 insertions, 1 deletions

diff --git a/erts/emulator/test/driver_SUITE.erl b/erts/emulator/test/driver_SUITE.erl
index 475e03087a..884f697384 100644
--- a/erts/emulator/test/driver_SUITE.erl
+++ b/erts/emulator/test/driver_SUITE.erl
@@ -80,6 +80,7 @@
          async_blast/1,
          thr_msg_blast/1,
          consume_timeslice/1,
+         env/1,
          z_test/1]).
 
 -export([bin_prefix/2]).
@@ -166,6 +167,7 @@ all() -> %% Keep a_test first and z_test last...
      async_blast,
      thr_msg_blast,
      consume_timeslice,
+     env,
      z_test].
 
 groups() -> 
@@ -2360,6 +2362,51 @@ count_proc_sched(Ps, PNs) ->
               PNs
     end.
 
+%%
+%% Tests whether erl_drv_putenv reflects in os:getenv and vice versa.
+%%
+env(Config) when is_list(Config) ->
+    ok = load_driver(proplists:get_value(data_dir, Config), env_drv),
+    Port = open_port({spawn_driver, env_drv}, []),
+    true = is_port(Port),
+
+    Keys = ["env_drv_a_key", "env_drv_b_key", "env_drv_c_key"],
+    Values = ["a_value", "b_value", "c_value"],
+
+    [env_put_test(Port, Key, Value) || Key <- Keys, Value <- Values],
+    [env_get_test(Port, Key, Value) || Key <- Keys, Value <- Values],
+    [env_oversize_test(Port, Key) || Key <- Keys],
+    [env_notfound_test(Port, Key) || Key <- Keys],
+
+    true = port_close(Port),
+    erl_ddll:unload_driver(env_drv),
+    ok.
+
+env_control(Port, Command, Key, Value) ->
+    KeyBin = list_to_binary(Key),
+    ValueBin = list_to_binary(Value),
+    Header = <<(byte_size(KeyBin)), (byte_size(ValueBin))>>,
+    Payload = <<KeyBin/binary, ValueBin/binary>>,
+    port_control(Port, Command, <<Header/binary, Payload/binary>>).
+
+env_put_test(Port, Key, Value) ->
+    os:unsetenv(Key),
+    [0] = env_control(Port, 0, Key, Value),
+    Value = os:getenv(Key).
+
+env_get_test(Port, Key, ExpectedValue) ->
+    true = os:putenv(Key, ExpectedValue),
+    [0] = env_control(Port, 1, Key, ExpectedValue).
+
+env_oversize_test(Port, Key) ->
+    os:putenv(Key, [$A || _ <- lists:seq(1, 1024)]),
+    [127] = env_control(Port, 1, Key, "").
+
+env_notfound_test(Port, Key) ->
+    true = os:unsetenv(Key),
+    [255] = env_control(Port, 1, Key, "").
+
+
 a_test(Config) when is_list(Config) ->
     rpc(Config, fun check_io_debug/0).
 
diff --git a/erts/emulator/test/driver_SUITE_data/Makefile.src b/erts/emulator/test/driver_SUITE_data/Makefile.src
index 1fedd72200..bcabaa689d 100644
--- a/erts/emulator/test/driver_SUITE_data/Makefile.src
+++ b/erts/emulator/test/driver_SUITE_data/Makefile.src
@@ -16,7 +16,8 @@ MISC_DRVS =		outputv_drv@dll@ \
 			thr_free_drv@dll@ \
 			async_blast_drv@dll@ \
 			thr_msg_blast_drv@dll@ \
-			consume_timeslice_drv@dll@
+			consume_timeslice_drv@dll@ \
+			env_drv@dll@
 
 SYS_INFO_DRVS = 	sys_info_base_drv@dll@ \
 			sys_info_prev_drv@dll@ \
diff --git a/erts/emulator/test/driver_SUITE_data/env_drv.c b/erts/emulator/test/driver_SUITE_data/env_drv.c
new file mode 100644
index 0000000000..0e910eeb84
--- /dev/null
+++ b/erts/emulator/test/driver_SUITE_data/env_drv.c
@@ -0,0 +1,108 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 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%
+ */
+
+/* Tests whether erl_drv_putenv/erl_drv_getenv work correctly and reflect
+ * changes to os:putenv/getenv. */
+
+#include <string.h>
+#include <stdio.h>
+
+#include "erl_driver.h"
+
+static ErlDrvSSizeT env_drv_ctl(ErlDrvData drv_data, unsigned int cmd,
+        char* buf, ErlDrvSizeT len, char** rbuf, ErlDrvSizeT rsize);
+
+static ErlDrvEntry env_drv_entry = { 
+    NULL /* init */,
+    NULL /* start */,
+    NULL /* stop */,
+    NULL /* output */,
+    NULL /* ready_input */,
+    NULL /* ready_output */,
+    "env_drv",
+    NULL /* finish */,
+    NULL /* handle */,
+    env_drv_ctl,
+    NULL /* timeout */,
+    NULL /* outputv*/,
+    NULL /* ready_async */,
+    NULL /* flush */,
+    NULL /* call*/,
+    NULL /* event */,
+    ERL_DRV_EXTENDED_MARKER,
+    ERL_DRV_EXTENDED_MAJOR_VERSION,
+    ERL_DRV_EXTENDED_MINOR_VERSION,
+    ERL_DRV_FLAG_USE_PORT_LOCKING,
+    NULL /* handle2 */,
+    NULL /* handle_monitor */
+};
+
+DRIVER_INIT(env_drv) {
+    return &env_drv_entry;
+}
+
+static int test_putenv(ErlDrvData drv_data, char *buf, ErlDrvSizeT len) {
+    char key[256], value[256];
+    int key_len, value_len;
+
+    key_len = buf[0];
+    value_len = buf[1];
+
+    sprintf(key, "%.*s", key_len, &buf[2]);
+    sprintf(value, "%.*s", value_len, &buf[2 + key_len]);
+
+    return erl_drv_putenv(key, value);
+}
+
+static int test_getenv(ErlDrvData drv_data, char *buf, ErlDrvSizeT len) {
+    char expected_value[256], stored_value[256], key[256];
+    int expected_value_len, key_len;
+    size_t stored_value_len;
+    int res;
+
+    key_len = buf[0];
+    sprintf(key, "%.*s", key_len, &buf[2]);
+
+    expected_value_len = buf[1];
+    sprintf(expected_value, "%.*s", expected_value_len, &buf[2 + key_len]);
+
+    stored_value_len = sizeof(stored_value);
+    res = erl_drv_getenv(key, stored_value, &stored_value_len);
+
+    if(res == 0) {
+        return strcmp(stored_value, expected_value) != 0;
+    } else if(res == 1) {
+        return 127;
+    }
+
+    return 255;
+}
+
+static ErlDrvSSizeT env_drv_ctl(ErlDrvData drv_data, unsigned int cmd,
+        char* buf, ErlDrvSizeT len, char** rbuf, ErlDrvSizeT rsize) {
+
+    if(cmd == 0) {
+        (**rbuf) = (char)test_putenv(drv_data, buf, len);
+    } else {
+        (**rbuf) = (char)test_getenv(drv_data, buf, len);
+    }
+
+    return 1;
+}