From be3c3a0e468237430ad7d19a33c60d306199a7f2 Mon Sep 17 00:00:00 2001 From: "Gregory P. Smith" Date: Sat, 24 Oct 2020 12:07:35 -0700 Subject: [PATCH] bpo-35823: Allow setsid() after vfork() on Linux. (GH-22945) It should just be a syscall updating a couple of fields in the kernel side process info. Confirming, in glibc is appears to be a shim for the setsid syscall (based on not finding any code implementing anything special for it) and in uclibc (*much* easier to read) it is clearly just a setsid syscall shim. A breadcrumb _suggesting_ that it is not allowed on Darwin/macOS comes from a commit in emacs: https://lists.gnu.org/archive/html/bug-gnu-emacs/2017-04/msg00297.html but I don't have a way to verify if that is true or not. As we are not supporting vfork on macOS today I just left a note in a comment. --- Modules/_posixsubprocess.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c index b7cba30ee76..8baea314f4e 100644 --- a/Modules/_posixsubprocess.c +++ b/Modules/_posixsubprocess.c @@ -38,6 +38,8 @@ #if defined(__linux__) && defined(HAVE_VFORK) && defined(HAVE_SIGNAL_H) && \ defined(HAVE_PTHREAD_SIGMASK) && !defined(HAVE_BROKEN_PTHREAD_SIGMASK) +/* If this is ever expanded to non-Linux platforms, verify what calls are + * allowed after vfork(). Ex: setsid() may be disallowed on macOS? */ # include # define VFORK_USABLE 1 #endif @@ -712,7 +714,6 @@ do_fork_exec(char *const exec_array[], #ifdef VFORK_USABLE if (child_sigmask) { /* These are checked by our caller; verify them in debug builds. */ - assert(!call_setsid); assert(!call_setuid); assert(!call_setgid); assert(!call_setgroups); @@ -997,7 +998,7 @@ subprocess_fork_exec(PyObject* self, PyObject *args) /* Use vfork() only if it's safe. See the comment above child_exec(). */ sigset_t old_sigs; if (preexec_fn == Py_None && - !call_setuid && !call_setgid && !call_setgroups && !call_setsid) { + !call_setuid && !call_setgid && !call_setgroups) { /* Block all signals to ensure that no signal handlers are run in the * child process while it shares memory with us. Note that signals * used internally by C libraries won't be blocked by