[libc++] Don't return uninitialized data from random_device::operator()

Make sure we appropriately retry calls to read if the return result is
less than what we asked for.

Additionally, check and handle IO errors: EINTR results in the read
operation getting restarted; other errors turn into exceptions.

llvm-svn: 210061

1 files changed, 16 insertions, 1 deletions

diff --git a/libcxx/src/random.cpp b/libcxx/src/random.cpp
index 21e21689a87..86017ef0d46 100644
--- a/libcxx/src/random.cpp
+++ b/libcxx/src/random.cpp
@@ -62,7 +62,22 @@ unsigned
 random_device::operator()()
 {
     unsigned r;
-    read(__f_, &r, sizeof(r));
+    size_t n = sizeof(r);
+    char* p = reinterpret_cast<char*>(&r);
+    while (n > 0)
+    {
+        ssize_t s = read(__f_, p, n);
+        if (s == 0)
+            __throw_system_error(ENODATA, "random_device got EOF");
+        if (s == -1)
+        {
+            if (errno != EINTR)
+                __throw_system_error(errno, "random_device got an unexpected error");
+            continue;
+        }
+        n -= static_cast<size_t>(s);
+        p += static_cast<size_t>(s);
+    }
     return r;
 }
 #endif // defined(_WIN32)