ext/pcntl: fix pcntl_setns() error handling.

Save errno into a local int before calling close(fd), as close() may
clobber errno on failure. Use int rather than errno_t because errno_t
is defined in C11 Annex K (bounds-checking interfaces) which is
optional and not widely implemented — many platforms (Linux/glibc,
musl, macOS, FreeBSD) do not provide it.

close GH-21256

NEWS

@@ -41,6 +41,10 @@ PHP                                                                        NEWS
 - OpenSSL:
   . Fix a bunch of leaks and error propagation. (ndossche)
 
+- PCNTL:
+  . Fixed pcntl_setns() internal errors handling regarding errnos.
+    (David Carlier)
+
 - PDO_PGSQL:
   . Fixed bug GH-21055 (connection attribute status typo for GSS negotiation).
     (lsaos)

ext/pcntl/pcntl.c

@@ -1584,7 +1584,7 @@ PHP_FUNCTION(pcntl_setns)
 
 	pid = pid_is_null ? getpid() : pid;
 	fd = syscall(SYS_pidfd_open, pid, 0);
-	if (errno) {
+	if (fd == -1) {
 		PCNTL_G(last_error) = errno;
 		switch (errno) {
 			case EINVAL:
@@ -1610,11 +1610,12 @@ PHP_FUNCTION(pcntl_setns)
 		RETURN_FALSE;
 	}
 	ret = setns(fd, (int)nstype);
+	int setns_errno = errno;
 	close(fd);
 
 	if (ret == -1) {
-		PCNTL_G(last_error) = errno;
-		switch (errno) {
+		PCNTL_G(last_error) = setns_errno;
+		switch (setns_errno) {
 			case ESRCH:
 				zend_argument_value_error(1, "process no longer available (" ZEND_LONG_FMT ")", pid);
 				RETURN_THROWS();
@@ -1624,11 +1625,11 @@ PHP_FUNCTION(pcntl_setns)
 				RETURN_THROWS();
 
 			case EPERM:
-				php_error_docref(NULL, E_WARNING, "Error %d: No required capability for this process", errno);
+				php_error_docref(NULL, E_WARNING, "Error %d: No required capability for this process", setns_errno);
 				break;
 
 			default:
-			        php_error_docref(NULL, E_WARNING, "Error %d", errno);
+			        php_error_docref(NULL, E_WARNING, "Error %d", setns_errno);
 		}
 		RETURN_FALSE;
 	} else {