From 57cb38b3833c5215131b983f181b26d6ba9b8d35 Mon Sep 17 00:00:00 2001 From: "Daniel P. Berrange" Date: Fri, 28 Aug 2015 14:40:01 +0100 Subject: osdep: add qemu_fork() wrapper for safely handling signals When using regular fork() the child process of course inherits all the parents' signal handlers. If the child then proceeds to close() any open file descriptors, it may break some of those registered signal handlers. The child generally does not want to ever run any of the signal handlers that the parent may have installed in the short time before it exec's. The parent may also have blocked various signals which the child process will want enabled. This introduces a wrapper qemu_fork() that takes care to sanitize signal handling across fork. Before forking it blocks all signals in the parent thread. After fork returns, the parent unblocks the signals and carries on as usual. The child, however, resets all the signal handlers back to their defaults before it unblocks signals. The child process can now exec the binary in a "clean" signal environment. Signed-off-by: Daniel P. Berrange --- include/qemu/osdep.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'include/qemu/osdep.h') diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index ef21efb..b568424 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -69,6 +69,8 @@ #include "sysemu/os-posix.h" #endif +#include "qapi/error.h" + #if defined(CONFIG_SOLARIS) && CONFIG_SOLARIS_VERSION < 10 /* [u]int_fast*_t not in */ typedef unsigned char uint_fast8_t; @@ -286,4 +288,18 @@ void os_mem_prealloc(int fd, char *area, size_t sz); int qemu_read_password(char *buf, int buf_size); +/** + * qemu_fork: + * + * A version of fork that avoids signal handler race + * conditions that can lead to child process getting + * signals that are otherwise only expected by the + * parent. It also resets all signal handlers to the + * default settings. + * + * Returns 0 to child process, pid number to parent + * or -1 on failure. + */ +pid_t qemu_fork(Error **errp); + #endif -- cgit v1.1