From c752eb55d9e9992bc38e7790128953427aa0a89f Mon Sep 17 00:00:00 2001
From: Frank Denis <github@pureftpd.org>
Date: Sun, 15 May 2016 17:18:50 +0200
Subject: [PATCH] On ancient Linux kernels, block on /dev/random before using
 /dev/urandom

---
 .../salsa20/randombytes_salsa20_random.c      | 33 +++++++++++++++++++
 .../sysrandom/randombytes_sysrandom.c         | 33 +++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c b/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
index 618ec81e..b71ce7e1 100644
--- a/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
+++ b/src/libsodium/randombytes/salsa20/randombytes_salsa20_random.c
@@ -7,6 +7,7 @@
 #endif
 #ifdef __linux__
 # include <sys/syscall.h>
+# include <poll.h>
 #endif
 
 #include <assert.h>
@@ -128,6 +129,33 @@ safe_read(const int fd, void * const buf_, size_t size)
 #endif
 
 #ifndef _WIN32
+# if defined(__linux__) && !defined(USE_BLOCKING_RANDOM)
+static int
+randombytes_block_on_dev_random(void)
+{
+    struct pollfd pfd;
+    int           fd;
+    int           pret;
+
+    fd = open("/dev/random", O_RDONLY);
+    if (fd == -1) {
+        return 0;
+    }
+    pfd.fd = fd;
+    pfd.events = POLLIN;
+    pfd.revents = 0;
+    do {
+        pret = poll(&pfd, 1, -1);
+    } while (pret < 0 && (errno == EINTR || errno == EAGAIN));
+    if (pret != 1) {
+        (void) close(fd);
+        errno = EIO;
+        return -1;
+    }
+    return close(fd);
+}
+# endif
+
 # ifndef HAVE_SAFE_ARC4RANDOM
 static int
 randombytes_salsa20_random_random_dev_open(void)
@@ -143,6 +171,11 @@ randombytes_salsa20_random_random_dev_open(void)
     const char **     device = devices;
     int               fd;
 
+# if defined(__linux__) && !defined(USE_BLOCKING_RANDOM)
+    if (randombytes_block_on_dev_random() != 0) {
+        return -1;
+    }
+# endif
     do {
         fd = open(*device, O_RDONLY);
         if (fd != -1) {
diff --git a/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c b/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c
index 62b1c760..f9277ae5 100644
--- a/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c
+++ b/src/libsodium/randombytes/sysrandom/randombytes_sysrandom.c
@@ -7,6 +7,7 @@
 #endif
 #ifdef __linux__
 # include <sys/syscall.h>
+# include <poll.h>
 #endif
 
 #include <assert.h>
@@ -107,6 +108,33 @@ safe_read(const int fd, void * const buf_, size_t size)
 #endif
 
 #ifndef _WIN32
+# if defined(__linux__) && !defined(USE_BLOCKING_RANDOM)
+static int
+randombytes_block_on_dev_random(void)
+{
+    struct pollfd pfd;
+    int           fd;
+    int           pret;
+
+    fd = open("/dev/random", O_RDONLY);
+    if (fd == -1) {
+        return 0;
+    }
+    pfd.fd = fd;
+    pfd.events = POLLIN;
+    pfd.revents = 0;
+    do {
+        pret = poll(&pfd, 1, -1);
+    } while (pret < 0 && (errno == EINTR || errno == EAGAIN));
+    if (pret != 1) {
+        (void) close(fd);
+        errno = EIO;
+        return -1;
+    }
+    return close(fd);
+}
+# endif
+
 static int
 randombytes_sysrandom_random_dev_open(void)
 {
@@ -121,6 +149,11 @@ randombytes_sysrandom_random_dev_open(void)
     const char **      device = devices;
     int                fd;
 
+# if defined(__linux__) && !defined(USE_BLOCKING_RANDOM)
+    if (randombytes_block_on_dev_random() != 0) {
+        return -1;
+    }
+# endif
     do {
         fd = open(*device, O_RDONLY);
         if (fd != -1) {