Update NSS to 3.38

- Added HACL*Poly1305 32-bit (INRIA/Microsoft)
- Updated to final TLS 1.3 draft version (28)
- Removed TLS 1.3 prerelease draft limit check
- Removed NPN code
- Enabled dev/urandom-only RNG on Linux with NSS_SEED_ONLY_DEV_URANDOM for non-standard environments
- Fixed several bugs with TLS 1.3 negotiation
- Updated internal certificate store
- Added support for the TLS Record Size Limit Extension.
- Fixed CVE-2018-0495
- Various security fixes in the ASN.1 code.

security/nss/lib/freebl/unix_urandom.c

@@ -4,10 +4,14 @@
 
 #include <fcntl.h>
 #include <unistd.h>
+#include <errno.h>
 #include "secerr.h"
 #include "secrng.h"
 #include "prprf.h"
 
+/* syscall getentropy() is limited to retrieving 256 bytes */
+#define GETENTROPY_MAX_BYTES 256
+
 void
 RNG_SystemInfoForRNG(void)
 {
@@ -28,6 +32,35 @@ RNG_SystemRNG(void *dest, size_t maxLen)
     size_t fileBytes = 0;
     unsigned char *buffer = dest;
 
+#if defined(__OpenBSD__) || (defined(LINUX) && defined(__GLIBC__) && ((__GLIBC__ > 2) || ((__GLIBC__ == 2) && (__GLIBC_MINOR__ >= 25))))
+    int result;
+
+    while (fileBytes < maxLen) {
+        size_t getBytes = maxLen - fileBytes;
+        if (getBytes > GETENTROPY_MAX_BYTES) {
+            getBytes = GETENTROPY_MAX_BYTES;
+        }
+        result = getentropy(buffer, getBytes);
+        if (result == 0) { /* success */
+            fileBytes += getBytes;
+            buffer += getBytes;
+        } else {
+            break;
+        }
+    }
+    if (fileBytes == maxLen) { /* success */
+        return maxLen;
+    }
+    /* If we failed with an error other than ENOSYS, it means the destination
+     * buffer is not writeable. We don't need to try writing to it again. */
+    if (errno != ENOSYS) {
+        PORT_SetError(SEC_ERROR_NEED_RANDOM);
+        return 0;
+    }
+    /* ENOSYS means the kernel doesn't support getentropy()/getrandom().
+     * Reset the number of bytes to get and fall back to /dev/urandom. */
+    fileBytes = 0;
+#endif
     fd = open("/dev/urandom", O_RDONLY);
     if (fd < 0) {
         PORT_SetError(SEC_ERROR_NEED_RANDOM);