2 files changed, 25 insertions, 15 deletions

diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-04-16-11-56-12.bpo-32849.aeSg-D.rst b/Misc/NEWS.d/next/Core and Builtins/2019-04-16-11-56-12.bpo-32849.aeSg-D.rst
new file mode 100644
index 0000000000..6a9a85c4b1
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-04-16-11-56-12.bpo-32849.aeSg-D.rst
@@ -0,0 +1,2 @@
+Fix Python Initialization code on FreeBSD to detect properly when stdin file
+descriptor (fd 0) is invalid.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index d8e6f8fa89..55d1ba5734 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -1672,26 +1672,34 @@ initsite(void)
 static int
 is_valid_fd(int fd)
 {
-#ifdef __APPLE__
-    /* bpo-30225: On macOS Tiger, when stdout is redirected to a pipe
-       and the other side of the pipe is closed, dup(1) succeed, whereas
-       fstat(1, &st) fails with EBADF. Prefer fstat() over dup() to detect
-       such error. */
-    struct stat st;
-    return (fstat(fd, &st) == 0);
-#else
-    int fd2;
-    if (fd < 0)
+/* dup() is faster than fstat(): fstat() can require input/output operations,
+   whereas dup() doesn't. There is a low risk of EMFILE/ENFILE at Python
+   startup. Problem: dup() doesn't check if the file descriptor is valid on
+   some platforms.
+
+   bpo-30225: On macOS Tiger, when stdout is redirected to a pipe and the other
+   side of the pipe is closed, dup(1) succeed, whereas fstat(1, &st) fails with
+   EBADF. FreeBSD has similar issue (bpo-32849).
+
+   Only use dup() on platforms where dup() is enough to detect invalid FD in
+   corner cases: on Linux and Windows (bpo-32849). */
+#if defined(__linux__) || defined(MS_WINDOWS)
+    if (fd < 0) {
         return 0;
+    }
+    int fd2;
+
     _Py_BEGIN_SUPPRESS_IPH
-    /* Prefer dup() over fstat(). fstat() can require input/output whereas
-       dup() doesn't, there is a low risk of EMFILE/ENFILE at Python
-       startup. */
     fd2 = dup(fd);
-    if (fd2 >= 0)
+    if (fd2 >= 0) {
         close(fd2);
+    }
     _Py_END_SUPPRESS_IPH
-    return fd2 >= 0;
+
+    return (fd2 >= 0);
+#else
+    struct stat st;
+    return (fstat(fd, &st) == 0);
 #endif
 }