Merge pull request #2300 from pi-hole/fix/randomness_crash

Prevent crash on failure to source secure randomness

src/config/password.c

@@ -93,8 +93,8 @@ static char * __attribute__((malloc)) double_sha256_password(const char *passwor
 
 bool get_secure_randomness(uint8_t *buffer, const size_t length)
 {
-	ssize_t result;
-
+	ssize_t result = -1;
+	const char *generator = "getrandom";
 	// First try to get randomness in non-blocking mode and print a warning when not enough entropy is available right now
 	do {
 		result = getrandom(buffer, length, GRND_NONBLOCK);
@@ -103,32 +103,51 @@ bool get_secure_randomness(uint8_t *buffer, const size_t length)
 	// If not enough entropy is available right now, try again in blocking mode
 	if (result < 0 && errno == EAGAIN)
 	{
-		log_warn("getrandom() failed in get_secure_randomness(): Not enough entropy available right now, retrying in blocking mode");
+		log_warn("Not enough entropy available right now for generating secure randomness, retrying in blocking mode");
 		// Sleep for 1 second to give the kernel some time to gather entropy
 		sleepms(1000);
 	}
 	else
 	{
 		// If the first try was successful, return the result
 		if (result >= 0)
-			return true;
+			goto random_success;
 	}
 	do {
 		result = getrandom(buffer, length, 0);
 	} while (result < 0 && errno == EINTR);
 
-	if (result < 0)
+	if(result < 0)
 	{
-		const int err = errno;
-		log_err("getrandom() failed in get_secure_randomness(): %s", strerror(errno));
-		errno = err;
-		return false;
+		log_debug(DEBUG_API, "Getting secure randomness failed (%s), trying /dev/urandom", strerror(errno));
+		generator = "/dev/urandom";
+		result = getrandom_fallback(buffer, length, 0);
+		if(result < 0 || result < (ssize_t)length)
+		{
+			log_debug(DEBUG_API, "Fallback failed, trying internal DRBG generator");
+			generator = "internal DRBG";
+			result = drbg_random(buffer, length);
+			if(result < 0)
+			{
+				// Warning will be printed by drbg_random()
+				return false;
+			}
+
+			log_debug(DEBUG_API, "Internal DRBG generator successfully used");
+		}
+		else
+			log_debug(DEBUG_API, "Fallback to /dev/urandom successful");
 	}
-	else if((size_t)result != length)
+
+	// Check if enough bytes were generated
+	if(result != (ssize_t)length)
 	{
-		log_err("getrandom() failed in get_secure_randomness(): Not enough bytes generated (%zu != %zu)", (size_t)result, length);
+		log_err("Randomness generator (%s) failed: not enough bytes generated (%zd != %zu)", generator, result, length);
 		return false;
 	}
+
+random_success:
+	log_debug(DEBUG_ANY, "Generated %zd bytes of secure randomness", result);
 	return true;
 }
 
@@ -185,7 +204,7 @@ static char * __attribute__((malloc)) balloon_password(const char *password,
 {
 	// Parameter check
 	if(password == NULL || salt == NULL)
-		return NULL;
+		return strdup("");
 
 	struct timespec start, end;
 	// Record starting time
@@ -370,7 +389,7 @@ char * __attribute__((malloc)) create_password(const char *password)
 	// genrandom() returns cryptographically secure random data
 	uint8_t salt[SALT_LEN] = { 0 };
 	if(!get_secure_randomness(salt, sizeof(salt)))
-		return NULL;
+		return strdup("");
 
 	// Generate balloon PHC-encoded password hash
 	return balloon_password(password, salt, true);

src/daemon.c

@@ -39,6 +39,8 @@
 #include <locale.h>
 // freeEnvVars()
 #include "config/env.h"
+// destroy_entropy()
+#include "webserver/x509.h"
 
 pthread_t threads[THREADS_MAX] = { 0 };
 bool resolver_ready = false;
@@ -425,6 +427,9 @@ void cleanup(const int ret)
 	// This should be the last action when c
 	destroy_shmem();
 
+	// De-initialize the random number generator and entropy collector
+	destroy_entropy();
+
 	// Free environment variables
 	freeEnvVars();
 

src/main.c

@@ -29,6 +29,8 @@
 #include "database/query-table.h"
 // verify_FTL()
 #include "files.h"
+// init_entropy()
+#include "webserver/x509.h"
 
 char *username;
 bool startup = true;
@@ -62,6 +64,9 @@ int main (int argc, char *argv[])
 	log_info("########## FTL started on %s! ##########", hostname());
 	log_FTL_version(false);
 
+	// Initialize entropy and random number generator
+	init_entropy();
+
 	// Catch signals not handled by dnsmasq
 	// We configure real-time signals later (after dnsmasq has forked)
 	handle_signals();