Clear PRNG states in FIPS mode.

FIPS requires that the CTR-DRBG state be zeroed on process exit, however
destructors for thread-local data aren't called when the process exits.

This change maintains a linked-list of thread-local state which is
walked on exit to zero each thread's PRNG state. Any concurrently
running threads block until the process finishes exiting.

Change-Id: Ie5dc18e1bb2941a569d8b309411cf20c9bdf52ef
Reviewed-on: https://boringssl-review.googlesource.com/16764
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

crypto/fipsmodule/rand/rand.c

@@ -18,12 +18,17 @@
 #include <limits.h>
 #include <string.h>
 
+#if defined(BORINGSSL_FIPS)
+#include <unistd.h>
+#endif
+
 #include <openssl/chacha.h>
 #include <openssl/cpu.h>
 #include <openssl/mem.h>
 
 #include "internal.h"
 #include "../../internal.h"
+#include "../delocate.h"
 
 
 /* It's assumed that the operating system always has an unfailing source of
@@ -55,22 +60,66 @@ struct rand_thread_state {
   /* calls is the number of generate calls made on |drbg| since it was last
    * (re)seeded. This is bound by |kReseedInterval|. */
   unsigned calls;
-  /* last_block contains the previous block from |CRYPTO_sysrand|. */
-  uint8_t last_block[CRNGT_BLOCK_SIZE];
   /* last_block_valid is non-zero iff |last_block| contains data from
    * |CRYPTO_sysrand|. */
   int last_block_valid;
+
+#if defined(BORINGSSL_FIPS)
+  /* last_block contains the previous block from |CRYPTO_sysrand|. */
+  uint8_t last_block[CRNGT_BLOCK_SIZE];
+  /* next and prev form a NULL-terminated, double-linked list of all states in
+   * a process. */
+  struct rand_thread_state *next, *prev;
+#endif
 };
 
+#if defined(BORINGSSL_FIPS)
+/* thread_states_list is the head of a linked-list of all |rand_thread_state|
+ * objects in the process, one per thread. This is needed because FIPS requires
+ * that they be zeroed on process exit, but thread-local destructors aren't
+ * called when the whole process is exiting. */
+DEFINE_BSS_GET(struct rand_thread_state *, thread_states_list);
+DEFINE_STATIC_MUTEX(thread_states_list_lock);
+
+static void rand_thread_state_clear_all(void) __attribute__((destructor));
+static void rand_thread_state_clear_all(void) {
+  CRYPTO_STATIC_MUTEX_lock_write(thread_states_list_lock_bss_get());
+  for (struct rand_thread_state *cur = *thread_states_list_bss_get();
+       cur != NULL; cur = cur->next) {
+    CTR_DRBG_clear(&cur->drbg);
+  }
+  /* |thread_states_list_lock is deliberately left locked so that any threads
+   * that are still running will hang if they try to call |RAND_bytes|. */
+}
+#endif
+
 /* rand_thread_state_free frees a |rand_thread_state|. This is called when a
  * thread exits. */
 static void rand_thread_state_free(void *state_in) {
+  struct rand_thread_state *state = state_in;
+
   if (state_in == NULL) {
     return;
   }
 
-  struct rand_thread_state *state = state_in;
+#if defined(BORINGSSL_FIPS)
+  CRYPTO_STATIC_MUTEX_lock_write(thread_states_list_lock_bss_get());
+
+  if (state->prev != NULL) {
+    state->prev->next = state->next;
+  } else {
+    *thread_states_list_bss_get() = state->next;
+  }
+
+  if (state->next != NULL) {
+    state->next->prev = state->prev;
+  }
+
+  CRYPTO_STATIC_MUTEX_unlock_write(thread_states_list_lock_bss_get());
+
   CTR_DRBG_clear(&state->drbg);
+#endif
+
   OPENSSL_free(state);
 }
 
@@ -202,7 +251,25 @@ void RAND_bytes_with_additional_data(uint8_t *out, size_t out_len,
       abort();
     }
     state->calls = 0;
+
+#if defined(BORINGSSL_FIPS)
+    if (state != &stack_state) {
+      CRYPTO_STATIC_MUTEX_lock_write(thread_states_list_lock_bss_get());
+      struct rand_thread_state **states_list = thread_states_list_bss_get();
+      state->next = *states_list;
+      if (state->next != NULL) {
+        state->next->prev = state;
       }
+      state->prev = NULL;
+      *states_list = state;
+      CRYPTO_STATIC_MUTEX_unlock_write(thread_states_list_lock_bss_get());
+    }
+#endif
+  }
+
+#if defined(BORINGSSL_FIPS)
+  CRYPTO_STATIC_MUTEX_lock_read(thread_states_list_lock_bss_get());
+#endif
 
   if (state->calls >= kReseedInterval) {
     uint8_t seed[CTR_DRBG_ENTROPY_LEN];
@@ -256,6 +323,10 @@ void RAND_bytes_with_additional_data(uint8_t *out, size_t out_len,
     CTR_DRBG_clear(&state->drbg);
   }
 
+#if defined(BORINGSSL_FIPS)
+  CRYPTO_STATIC_MUTEX_unlock_read(thread_states_list_lock_bss_get());
+#endif
+
   return;
 }
 

crypto/thread_test.c

@@ -15,6 +15,7 @@
 #include "internal.h"
 
 #include <openssl/crypto.h>
+#include <openssl/rand.h>
 
 #include <stdio.h>
 
@@ -232,9 +233,32 @@ static int test_thread_local(void) {
   return 1;
 }
 
+static void rand_state_test_thread(void) {
+  uint8_t buf[1];
+  RAND_bytes(buf, sizeof(buf));
+}
+
+static int test_rand_state(void) {
+  /* In FIPS mode, rand.c maintains a linked-list of thread-local data because
+   * we're required to clear it on process exit. This test exercises removing a
+   * value from that list. */
+  uint8_t buf[1];
+  RAND_bytes(buf, sizeof(buf));
+
+  thread_t thread;
+  if (!run_thread(&thread, rand_state_test_thread) ||
+      !wait_for_thread(thread)) {
+    fprintf(stderr, "thread failed.\n");
+    return 0;
+  }
+
+  return 1;
+}
+
 int main(int argc, char **argv) {
   if (!test_once() ||
-      !test_thread_local()) {
+      !test_thread_local() ||
+      !test_rand_state()) {
     return 1;
   }