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, 12 insertions, 7 deletions

diff --git a/erts/emulator/beam/utils.c b/erts/emulator/beam/utils.c
index 993585be10..fe9f1c7606 100644
--- a/erts/emulator/beam/utils.c
+++ b/erts/emulator/beam/utils.c
@@ -4360,15 +4360,20 @@ erts_read_env(char *key)
     char *value = erts_alloc(ERTS_ALC_T_TMP, value_len);
     int res;
     while (1) {
-	res = erts_sys_getenv_raw(key, value, &value_len);
-	if (res <= 0)
-	    break;
-	value = erts_realloc(ERTS_ALC_T_TMP, value, value_len);
+        res = erts_sys_explicit_8bit_getenv(key, value, &value_len);
+
+        if (res >= 0) {
+            break;
+        }
+
+        value = erts_realloc(ERTS_ALC_T_TMP, value, value_len);
     }
-    if (res != 0) {
-	erts_free(ERTS_ALC_T_TMP, value);
-	return NULL;
+
+    if (res != 1) {
+        erts_free(ERTS_ALC_T_TMP, value);
+        return NULL;
     }
+
     return value;
 }