gh-138401: Check arg count>=0 in os.sendfile

Lib/test/test_os.py

@@ -3957,6 +3957,11 @@ async def test_invalid_offset(self):
             await self.async_sendfile(self.sockno, self.fileno, -1, 4096)
         self.assertEqual(cm.exception.errno, errno.EINVAL)
 
+    async def test_invalid_count(self):
+        with self.assertRaises(ValueError, msg="count cannot be negative"):
+            await self.sendfile_wrapper(self.sockno, self.fileno, offset=0,
+                                        count=-1)
+
     async def test_keywords(self):
         # Keyword arguments should be supported
         await self.async_sendfile(out_fd=self.sockno, in_fd=self.fileno,

Misc/NEWS.d/next/Core_and_Builtins/2025-09-02-22-17-55.gh-issue-138401.uTRvue.rst

@@ -0,0 +1,2 @@
+Add missing validation of argument ``count`` in :func:`os.sendfile` to be
+non-negative.

Modules/posixmodule.c

@@ -11874,7 +11874,7 @@ os.sendfile
     out_fd: int
     in_fd: int
     offset: Py_off_t
-    count: Py_ssize_t
+    count: Py_ssize_t(allow_negative=False)
     headers: object(c_default="NULL") = ()
     trailers: object(c_default="NULL") = ()
     flags: int = 0
@@ -11886,28 +11886,38 @@ static PyObject *
 os_sendfile_impl(PyObject *module, int out_fd, int in_fd, Py_off_t offset,
                  Py_ssize_t count, PyObject *headers, PyObject *trailers,
                  int flags)
-/*[clinic end generated code: output=329ea009bdd55afc input=338adb8ff84ae8cd]*/
+/*[clinic end generated code: output=329ea009bdd55afc input=dcb026b94effa922]*/
 #else
 /*[clinic input]
 os.sendfile
 
     out_fd: int
     in_fd: int
     offset as offobj: object
-    count: Py_ssize_t
+    count: Py_ssize_t(allow_negative=False)
 
 Copy count bytes from file descriptor in_fd to file descriptor out_fd.
 [clinic start generated code]*/
 
 static PyObject *
 os_sendfile_impl(PyObject *module, int out_fd, int in_fd, PyObject *offobj,
                  Py_ssize_t count)
-/*[clinic end generated code: output=ae81216e40f167d8 input=76d64058c74477ba]*/
+/*[clinic end generated code: output=ae81216e40f167d8 input=424df0949059ea5b]*/
 #endif
 {
     Py_ssize_t ret;
     int async_err = 0;
 
+#ifdef __APPLE__
+    if(sbytes < 0) {
+        PyErr_SetString(PyExc_ValueError,
+                        "count cannot be negative");
+        return NULL;
+    }
+#else
+    assert(count >= 0);
+#endif
+
 #if defined(__FreeBSD__) || defined(__DragonFly__) || defined(__APPLE__)
 #ifndef __APPLE__
     off_t sbytes;