Fix localtime/1 mem leak

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Stop using deprecated `term_from_int32` on RP2 platform
 - Stop using deprecated `term_from_int32` on ESP32 platform
 - Fixed improper cast of ESP32 `event_data` for `WIFI_EVENT_AP_STA(DIS)CONNECTED` events
+- Fixed `erlang:localtime/1` memory leak, use-after-free, and TZ restore bugs on newlib/picolibc
 
 ## [0.7.0-alpha.1] - 2026-04-06
 

src/libAtomVM/nifs.c

@@ -1949,6 +1949,64 @@ term nif_erlang_universaltime_0(Context *ctx, int argc, term argv[])
     return build_datetime_from_tm(ctx, gmtime_r(&ts.tv_sec, &broken_down_time));
 }
 
+// Workaround for newlib/picolibc setenv memory leak: use putenv with a
+// fixed-size static buffer. The buffer is installed once via putenv and then
+// modified in place so repeated TZ changes never allocate.
+// See: https://github.com/espressif/esp-idf/issues/3046
+// Both newlib and picolibc leak the old "NAME=value" string on overwrite.
+#if defined(__NEWLIB__) || defined(__PICOLIBC__)
+#define AVM_TZ_SETENV_LEAKS 1
+#else
+#define AVM_TZ_SETENV_LEAKS 0
+#endif
+
+#if AVM_TZ_SETENV_LEAKS
+
+// Max TZ value length is 60 bytes; longest POSIX TZ strings (e.g.
+// "CET-1CEST,M3.5.0/2,M10.5.0/3") are well under this limit.
+#define TZ_BUFFER_SIZE 64
+#define TZ_MAX_VALUE_LEN (TZ_BUFFER_SIZE - 4) // 3 for "TZ=" + 1 for '\0'
+
+static char tz_buffer[TZ_BUFFER_SIZE] = "TZ=";
+static bool tz_buffer_installed = false;
+// Cached pointer into the environment; assumes AtomVM is the sole user of TZ
+// (no external threads reading or writing TZ or calling time functions
+// that depend on it during the temporary override).
+static char *tz_env_value = NULL;
+
+// Write a TZ value into the static buffer. Returns false if the value is
+// too long to fit (the buffer is left unchanged in that case).
+// Caller must hold env_spinlock.
+static bool set_static_tz_value(const char *tz)
+{
+    size_t tz_len = strlen(tz);
+    if (tz_len > TZ_MAX_VALUE_LEN) {
+        return false;
+    }
+    if (!tz_buffer_installed) {
+        // Install a full-width placeholder first. Some libc implementations
+        // copy the environment string instead of keeping our static buffer, and
+        // installing just "TZ=" would leave too little storage for later
+        // in-place updates.
+        memset(tz_buffer + 3, ' ', TZ_MAX_VALUE_LEN);
+        tz_buffer[3 + TZ_MAX_VALUE_LEN] = '\0';
+        if (putenv(tz_buffer) != 0) {
+            return false;
+        }
+        tz_buffer_installed = true;
+        tz_env_value = getenv("TZ");
+        if (tz_env_value == NULL) {
+            tz_env_value = tz_buffer + 3;
+        }
+    }
+    memcpy(tz_env_value, tz, tz_len);
+    memset(tz_env_value + tz_len, 0, TZ_MAX_VALUE_LEN - tz_len);
+    tz_env_value[TZ_MAX_VALUE_LEN] = '\0';
+    return true;
+}
+
+#endif // AVM_TZ_SETENV_LEAKS
+
 term nif_erlang_localtime(Context *ctx, int argc, term argv[])
 {
     char *tz;
@@ -1972,17 +2030,62 @@ term nif_erlang_localtime(Context *ctx, int argc, term argv[])
     smp_spinlock_lock(&ctx->global->env_spinlock);
 #endif
     if (tz) {
-        char *oldtz = getenv("TZ");
+        char *oldtz = NULL;
+        char *oldtz_env = getenv("TZ");
+        if (oldtz_env) {
+            oldtz = strdup(oldtz_env);
+            if (UNLIKELY(oldtz == NULL)) {
+#ifndef AVM_NO_SMP
+                smp_spinlock_unlock(&ctx->global->env_spinlock);
+#endif
+                free(tz);
+                RAISE_ERROR(OUT_OF_MEMORY_ATOM);
+            }
+        }
+
+#if AVM_TZ_SETENV_LEAKS
+        if (!set_static_tz_value(tz)) {
+#ifndef AVM_NO_SMP
+            smp_spinlock_unlock(&ctx->global->env_spinlock);
+#endif
+            free(oldtz);
+            free(tz);
+            RAISE_ERROR(BADARG_ATOM);
+        }
+#else
         setenv("TZ", tz, 1);
+#endif
         tzset();
         localtime = localtime_r(&ts.tv_sec, &storage);
+
         if (oldtz) {
+#if AVM_TZ_SETENV_LEAKS
+            if (!set_static_tz_value(oldtz)) {
+                setenv("TZ", oldtz, 1);
+                tz_env_value = getenv("TZ");
+            }
+#else
             setenv("TZ", oldtz, 1);
+#endif
+            free(oldtz);
         } else {
+#if AVM_TZ_SETENV_LEAKS
+            // Cannot truly unset TZ with the static buffer approach;
+            // putenv does not support removal.
+            // NOTE: This is a pragmatic approximation, not a true restore.
+            // When TZ was originally unset, setting it to "UTC0" permanently
+            // changes observable process state (getenv("TZ") will return
+            // "UTC0" instead of NULL). This is acceptable on newlib/picolibc
+            // embedded targets where unset TZ already defaults to UTC.
+            if (!set_static_tz_value("UTC0")) {
+                unsetenv("TZ");
+            }
+#else
             unsetenv("TZ");
+#endif
         }
+        tzset();
     } else {
-        // Call tzset to handle DST changes
         tzset();
         localtime = localtime_r(&ts.tv_sec, &storage);
     }
@@ -1991,6 +2094,11 @@ term nif_erlang_localtime(Context *ctx, int argc, term argv[])
 #endif
 
     free(tz);
+
+    if (UNLIKELY(localtime == NULL)) {
+        RAISE_ERROR(BADARG_ATOM);
+    }
+
     return build_datetime_from_tm(ctx, localtime);
 }