From 2e93d8dc2810533bae2a6b3f2a3b2258e5491b8b Mon Sep 17 00:00:00 2001
From: LoRd_MuldeR <mulder2@gmx.de>
Date: Sat, 17 Apr 2021 16:05:32 +0200
Subject: [PATCH] Fall back to /dev/urandom, if compiled with getrandom()
 support but that syscall is not available at runtime.

---
 libslunkcrypt/src/junk.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/libslunkcrypt/src/junk.c b/libslunkcrypt/src/junk.c
index 112fdd9..b111c75 100644
--- a/libslunkcrypt/src/junk.c
+++ b/libslunkcrypt/src/junk.c
@@ -48,7 +48,7 @@
 
 /* detect explicit_bzero() support */
 #undef EXPLICIT_BZERO
-#if defined(_WIN32)	&& defined(SecureZeroMemory)
+#if defined(_WIN32) && defined(SecureZeroMemory)
 #	define EXPLICIT_BZERO SecureZeroMemory
 #elif defined(__GLIBC__) && (__GLIBC__ >= 2) && (__GLIBC_MINOR__ >= 25)
 #	define EXPLICIT_BZERO explicit_bzero
@@ -97,7 +97,7 @@ static CALL_ONCE_TYPE s_random_is_initialized = CALL_ONCE_INIT;
 typedef BOOLEAN(WINAPI *rtlgenrandom_t)(void *buffer, ULONG buff_size);
 static HMODULE s_advapi32 = NULL;
 static rtlgenrandom_t s_rtlgenrandom = NULL;
-#elif !defined(SYS_GETRANDOM)
+#else
 static const char *const DEV_RANDOM[] = { "/dev/urandom", "/dev/arandom", "/dev/random", NULL };
 static int s_random_fd = -1;
 #endif
@@ -112,7 +112,7 @@ static void exit_random_source(void)
 		FreeLibrary(s_advapi32);
 		s_advapi32 = NULL;
 	}
-#elif !defined(SYS_GETRANDOM)
+#else
 	if (s_random_fd >= 0)
 	{
 		close(s_random_fd);
@@ -129,14 +129,22 @@ static void init_random_source(void)
 	{
 		s_rtlgenrandom = (rtlgenrandom_t) GetProcAddress(s_advapi32, "SystemFunction036");
 	}
-#elif !defined(SYS_GETRANDOM)
+#else
+#if defined(SYS_GETRANDOM)
+	uint8_t temp;
+	if (getrandom(&temp, 0U, 0U) >= 0)
+	{
+		goto init_completed;
+	}
+#endif
 	for (size_t i = 0U; DEV_RANDOM[i]; ++i)
 	{
 		if ((s_random_fd = open(DEV_RANDOM[i], O_RDONLY)) >= 0)
 		{
-			break; /*success*/
+			goto init_completed;
 		}
 	}
+init_completed: ;
 #endif
 #if !defined(ATTRIB_DESTRUCTOR)
 	atexit(exit_random_source);
@@ -153,15 +161,19 @@ size_t slunkcrypt_random_bytes(uint8_t* const buffer, const size_t length)
 		const ULONG buff_size = (ULONG)length;
 		return s_rtlgenrandom(buffer, buff_size) ? buff_size : 0U;
 	}
-#elif defined(SYS_GETRANDOM)
-	const ssize_t result = getrandom(buffer, length, 0U);
-	return (result < 0) ? 0U : ((size_t)result);
 #else
 	if (s_random_fd >= 0)
 	{
 		const ssize_t result = read(s_random_fd, buffer, length);
 		return (result < 0) ? 0U : ((size_t)result);
 	}
+#if defined(SYS_GETRANDOM)
+	else
+	{
+		const ssize_t result = getrandom(buffer, length, 0U);
+		return (result < 0) ? 0U : ((size_t)result);
+	}
+#endif
 #endif
 	return 0U;
 }