diff options
| -rw-r--r-- | include/qemu/osdep.h | 16 | ||||
| -rw-r--r-- | util/oslib-posix.c | 71 | ||||
| -rw-r--r-- | util/oslib-win32.c | 9 |
3 files changed, 96 insertions, 0 deletions
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index ef21efb683..b56842420e 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 <sys/int_types.h> */ 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 diff --git a/util/oslib-posix.c b/util/oslib-posix.c index a0fcdc2ede..40249183e6 100644 --- a/util/oslib-posix.c +++ b/util/oslib-posix.c @@ -490,3 +490,74 @@ int qemu_read_password(char *buf, int buf_size) printf("\n"); return ret; } + + +pid_t qemu_fork(Error **errp) +{ + sigset_t oldmask, newmask; + struct sigaction sig_action; + int saved_errno; + pid_t pid; + + /* + * Need to block signals now, so that child process can safely + * kill off caller's signal handlers without a race. + */ + sigfillset(&newmask); + if (pthread_sigmask(SIG_SETMASK, &newmask, &oldmask) != 0) { + error_setg_errno(errp, errno, + "cannot block signals"); + return -1; + } + + pid = fork(); + saved_errno = errno; + + if (pid < 0) { + /* attempt to restore signal mask, but ignore failure, to + * avoid obscuring the fork failure */ + (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL); + error_setg_errno(errp, saved_errno, + "cannot fork child process"); + errno = saved_errno; + return -1; + } else if (pid) { + /* parent process */ + + /* Restore our original signal mask now that the child is + * safely running. Only documented failures are EFAULT (not + * possible, since we are using just-grabbed mask) or EINVAL + * (not possible, since we are using correct arguments). */ + (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL); + } else { + /* child process */ + size_t i; + + /* Clear out all signal handlers from parent so nothing + * unexpected can happen in our child once we unblock + * signals */ + sig_action.sa_handler = SIG_DFL; + sig_action.sa_flags = 0; + sigemptyset(&sig_action.sa_mask); + + for (i = 1; i < NSIG; i++) { + /* Only possible errors are EFAULT or EINVAL The former + * won't happen, the latter we expect, so no need to check + * return value */ + (void)sigaction(i, &sig_action, NULL); + } + + /* Unmask all signals in child, since we've no idea what the + * caller's done with their signal mask and don't want to + * propagate that to children */ + sigemptyset(&newmask); + if (pthread_sigmask(SIG_SETMASK, &newmask, NULL) != 0) { + Error *local_err = NULL; + error_setg_errno(&local_err, errno, + "cannot unblock signals"); + error_report_err(local_err); + _exit(1); + } + } + return pid; +} diff --git a/util/oslib-win32.c b/util/oslib-win32.c index 08f5a9cda2..09f9e98a40 100644 --- a/util/oslib-win32.c +++ b/util/oslib-win32.c @@ -496,3 +496,12 @@ int qemu_read_password(char *buf, int buf_size) buf[i] = '\0'; return 0; } + + +pid_t qemu_fork(Error **errp) +{ + errno = ENOSYS; + error_setg_errno(errp, errno, + "cannot fork child process"); + return -1; +} |