Bug 1057343, Use Linux getrandom()/getentropy() kernel system call for obtaining entropy, r=fkiefer

2 files changed, 37 insertions, 0 deletions

diff --git a/coreconf/config.mk b/coreconf/config.mk
index 55d95c30e..b62f6cef4 100644
--- a/coreconf/config.mk
+++ b/coreconf/config.mk
@@ -181,6 +181,10 @@ ifndef NSS_FORCE_FIPS
 DEFINES += -DNSS_NO_INIT_SUPPORT
 endif
 
+ifdef NSS_SEED_ONLY_DEV_URANDOM
+DEFINES += -DSEED_ONLY_DEV_URANDOM
+endif
+
 # Avoid building object leak test code for optimized library
 ifndef BUILD_OPT
 ifdef PKIX_OBJECT_LEAK_TEST
diff --git a/lib/freebl/unix_urandom.c b/lib/freebl/unix_urandom.c
index 25e6ad91c..4c65d8fe5 100644
--- a/lib/freebl/unix_urandom.c
+++ b/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(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);