[New-bugs-announce] [issue41033] readline.c: SEGFAULT on SIGWINCH when loaded twice

[daniel hahler]

New submission from daniel hahler <python-bugs at thequod.de>:

The following will crash due to the signal handler calling itself recursively:

```
import os, readline, signal, sys

del sys.modules["readline"]
import readline

os.kill(os.getpid(), signal.SIGWINCH)
```

This fixes it:
```
diff --git a/Modules/readline.c b/Modules/readline.c
index 081657fb23..174e0117a9 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -967,6 +967,7 @@ readline_sigwinch_handler(int signum)
 {
     sigwinch_received = 1;
     if (sigwinch_ohandler &&
+            sigwinch_ohandler != readline_sigwinch_handler &&
             sigwinch_ohandler != SIG_IGN && sigwinch_ohandler != SIG_DFL)
         sigwinch_ohandler(signum);

```

It gets installed/saved in https://github.com/python/cpython/blob/01ece63d42b830df106948db0aefa6c1ba24416a/Modules/readline.c#L1111-L1112.

Maybe it could also not save it in the first place if it is itself / has been installed already.

Or, it could be uninstalled when the module is unloaded, if there is such a thing?

I've seen the crash initially in a more complex setup, where it is not really clear why/how the readline module gets initialized twice really, but the above appears to simulate the situation.
(Hints on where to break in gdb to see where/when a module gets unloaded would be appreciated)

Added in https://github.com/python/cpython/commit/5dbbf1abba89ef1766759fbc9d5a5af02db49505 (3.5.2).

----------
components: Extension Modules
messages: 371861
nosy: blueyed
priority: normal
severity: normal
status: open
title: readline.c: SEGFAULT on SIGWINCH when loaded twice
type: crash
versions: Python 3.10, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41033>
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