Fix

Author: corona10

Doc/library/mmap.rst

@@ -333,7 +333,7 @@ To map anonymous memory, -1 should be passed as the fileno along with the length
       Annotate the memory mapping with the given *name* for easier identification
       in ``/proc/<pid>/maps`` if the kernel supports the feature and :option:`-X dev <-X>` is passed
       to Python or if Python is built in :ref:`debug mode <debug-build>`
-      The length of *name* must not exceed 67 bytes.
+      The length of *name* must not exceed 67 bytes including '\0'
 
       .. availability:: Linux >= 5.17 (kernel built with ``CONFIG_ANON_VMA_NAME`` option)
 

Include/internal/pycore_mmap.h

@@ -25,6 +25,7 @@ _PyAnnotateMemoryMap(void *addr, size_t size, const char *name)
         return;
     }
 #endif
+    // The name length cannot exceed 80 (including the '\0').
     assert(strlen(name) < 80);
     int old_errno = errno;
     prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, (unsigned long)addr, size, name);

Lib/test/test_mmap.py

@@ -1174,14 +1174,14 @@ def test_set_name(self):
         result = m.set_name('test_mapping')
         self.assertIsNone(result)
 
-        # Test name length limit (80 chars including prefix "cpython:mmap:")
-        # Prefix is 13 chars, so max name is 67 chars
-        long_name = 'x' * 67
+        # Test name length limit (80 chars including prefix "cpython:mmap:" and '\0')
+        # Prefix is 13 chars, so max name is 66 chars
+        long_name = 'x' * 66
         result = m.set_name(long_name)
         self.assertIsNone(result)
 
         # Test name too long
-        too_long_name = 'x' * 68
+        too_long_name = 'x' * 67
         with self.assertRaises(ValueError):
             m.set_name(too_long_name)
 

Modules/mmapmodule.c

@@ -1133,12 +1133,12 @@ mmap_mmap_set_name_impl(mmap_object *self, const char *name)
 {
 #if defined(MAP_ANONYMOUS) && defined(__linux__)
     const char *prefix = "cpython:mmap:";
-    if (strlen(name) + strlen(prefix) > 80) {
+    if (strlen(name) + strlen(prefix) > 79) {
         PyErr_SetString(PyExc_ValueError, "name is too long");
         return NULL;
     }
     if (self->flags & MAP_ANONYMOUS) {
-        char buf[81];
+        char buf[80];
         sprintf(buf, "%s%s", prefix, name);
         _PyAnnotateMemoryMap(self->data, self->size, buf);
         Py_RETURN_NONE;