Assertion failure for socket with too large default timeout (larger than INT_MAX)

[devdanzin]

Crash report

What happened?

A debug build will abort when calling socket._fallback_socketpair() after a call to socket.setdefaulttimeout with too high a value:

python -c "import socket; socket.setdefaulttimeout(2**31) ; socket._fallback_socketpair()"
python: ./Modules/socketmodule.c:819: internal_select: Assertion `ms <= INT_MAX' failed.
Aborted (core dumped)

Found using fusil by @vstinner.

CPython versions tested on:

3.12, 3.13, 3.14, CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.13.0+ (heads/3.13:7be8743, Nov 15 2024, 15:20:16) [GCC 13.2.0]

Linked PRs

• gh-126876: Fix socket internal_select() for large timeout #126968
• [3.13] gh-126876: Fix socket internal_select() for large timeout (GH-126968) #127002
• [3.12] gh-126876: Fix socket internal_select() for large timeout (GH-126968) #127003
• gh-126876: Fix test_socket.testLargeTimeout() for missing _testcapi #127517

[sobolevn]

Here's my idea:

diff --git Modules/socketmodule.c Modules/socketmodule.c
index 2764bd6e2b2..4c0aac92a76 100644
--- Modules/socketmodule.c
+++ Modules/socketmodule.c
@@ -810,7 +810,7 @@ internal_select(PySocketSockObject *s, int writing, PyTime_t interval,
 
     /* s->sock_timeout is in seconds, timeout in ms */
     ms = _PyTime_AsMilliseconds(interval, _PyTime_ROUND_CEILING);
-    assert(ms <= INT_MAX);
+    assert(ms <= PyTime_MAX);
 
     /* On some OSes, typically BSD-based ones, the timeout parameter of the
        poll() syscall, when negative, must be exactly INFTIM, where defined,
                                               

After that:

» ./python.exe -c "import socket; socket.setdefaulttimeout(2**31) ; socket._fallback_socketpair()"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import socket; socket.setdefaulttimeout(2**31) ; socket._fallback_socketpair()
                                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/Users/sobolev/Desktop/cpython2/Lib/socket.py", line 633, in _fallback_socketpair
    ssock, _ = lsock.accept()
               ~~~~~~~~~~~~^^
  File "/Users/sobolev/Desktop/cpython2/Lib/socket.py", line 298, in accept
    fd, addr = self._accept()
               ~~~~~~~~~~~~^^
TimeoutError: timed out
                       

[sobolevn]

If others agree with me - I can open a PR :)

[vstinner]

-    assert(ms <= INT_MAX);
+    assert(ms <= PyTime_MAX);

This change is wrong: poll() last argument type is int. A better fix would be:

diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 2764bd6e2b2..0ba5b4af6bc 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -810,7 +810,9 @@ internal_select(PySocketSockObject *s, int writing, PyTime_t interval,
 
     /* s->sock_timeout is in seconds, timeout in ms */
     ms = _PyTime_AsMilliseconds(interval, _PyTime_ROUND_CEILING);
-    assert(ms <= INT_MAX);
+    if (ms > INT_MAX) {
+        ms = INT_MAX;
+    }
 
     /* On some OSes, typically BSD-based ones, the timeout parameter of the
        poll() syscall, when negative, must be exactly INFTIM, where defined,

[vstinner]

I propose PR gh-126968 to fix the issue.