unixfd: Fix assertion failure constructing UnixFd for invalid fd

File descriptors are represented as the C int type, but only non-negative
values represent a valid fd, with all negative values representing the
absence of a fd (a NULL-like value).

Previously, make_fd() accepted negative fds, but then UnixFd_tp_new
would crash with an assertion failure. Instead, range-check the value
according to the semantically valid range. If it isn't, raise the same
error we previously raised for values that don't fit in an int.

Signed-off-by: Simon McVittie <smcv@collabora.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/dbus_bindings/unixfd.c b/dbus_bindings/unixfd.c
index 63a2402..e515cd3 100644
--- a/dbus_bindings/unixfd.c
+++ b/dbus_bindings/unixfd.c
@@ -62,9 +62,9 @@ typedef struct {
 } UnixFdObject;
 
 /* Return values:
- * -2 - the long value overflows an int
+ * -2 - the long value is not plausible as a file descriptor
  * -1 - Python failed producing a long (or in Python 2 an int)
- *  0 - success
+ *  0 - success (value might not *actually* be a fd, but it *could* be)
  *  1 - arg is not a long (or in Python 2 an int)
  *
  * Or to summarize:
@@ -89,7 +89,7 @@ make_fd(PyObject *arg, int *fd)
         return 1;
     }
     /* Check for int overflow. */
-    if (fd_arg < INT_MIN || fd_arg > INT_MAX) {
+    if (fd_arg < 0 || fd_arg > INT_MAX) {
         PyErr_Format(PyExc_ValueError, "int is outside fd range");
         return -2;
     }