Merge support for getrandom() call

ChangeLog

@@ -31,6 +31,8 @@ Features
    * Support for 1/n-1 record splitting, a countermeasure against BEAST.
    * Certificate selection based on signature hash, prefering SHA-1 over SHA-2
      for pre-1.2 clients when multiple certificates are available.
+   * Add support for getrandom() syscall on recent Linux kernels with Glibc or
+     a compatible enough libc (eg uClibc).
 
 Bugfix
    * Stack buffer overflow if ctr_drbg_update() is called with too large

library/entropy_poll.c

@@ -73,6 +73,43 @@ int platform_entropy_poll( void *data, unsigned char *output, size_t len,
 }
 #else /* _WIN32 && !EFIX64 && !EFI32 */
 
+/*
+ * Test for Linux getrandom() support.
+ * Since there is no wrapper in the libc yet, use the generic syscall wrapper
+ * available in GNU libc and compatible libc's (eg uClibc).
+ */
+#if defined(__linux__) && defined(__GLIBC__)
+#include <linux/version.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#if defined(SYS_getrandom)
+#define HAVE_GETRANDOM
+static int getrandom_wrapper( void *buf, size_t buflen, unsigned int flags )
+{
+    return( syscall( SYS_getrandom, buf, buflen, flags ) );
+}
+#endif /* SYS_getrandom */
+#endif /* __linux__ */
+
+#if defined(HAVE_GETRANDOM)
+
+#include <errno.h>
+
+int platform_entropy_poll( void *data,
+                           unsigned char *output, size_t len, size_t *olen )
+{
+    int ret;
+    ((void) data);
+
+    if( ( ret = getrandom_wrapper( output, len, 0 ) ) < 0 )
+        return( POLARSSL_ERR_ENTROPY_SOURCE_FAILED );
+
+    *olen = ret;
+    return( 0 );
+}
+
+#else /* HAVE_GETRANDOM */
+
 #include <stdio.h>
 
 int platform_entropy_poll( void *data,
@@ -100,6 +137,7 @@ int platform_entropy_poll( void *data,
 
     return( 0 );
 }
+#endif /* HAVE_GETRANDOM */
 #endif /* _WIN32 && !EFIX64 && !EFI32 */
 #endif /* !POLARSSL_NO_PLATFORM_ENTROPY */