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xwayland: do not snprintf() after fork()

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Between fork() and exec() in the child process it is only safe to use
async-signal-safe functions. Surprisingly, snprintf() is not such
function. See e.g. https://stackoverflow.com/a/6771799 and how snprintf
is not listed in signal-safety(7) manual.

Therefore we must prepare the fd argument strings before fork(). That is
only possible if we also do not dup() fd in the child process. Hence we
remove the close-on-exec flag instead in the child process which has
copies of the parent's file descriptors. Fortunately fcntl() is safe.

struct fdstr is helping to reduce code clutter a bit.

Additionally, if fork() fails, we now clean up the fds we created.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This commit is contained in:
Pekka Paalanen 2022-07-07 14:18:54 +03:00 • committed by Pekka Paalanen
parent 99b2b958f9
commit 4c0bdbfde9
1 changed files with 72 additions and 36 deletions
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108
compositor/xwayland.c
View file

@ -89,16 +89,40 @@ out:
return 0;
}
/* Duplicate an FD and write it into a string, for use in environment */
#define FD_STR_LEN 12
static bool
dup_fd_to_string(char s[FD_STR_LEN], int fd)
struct fdstr {
char str1[12];
int fds[2];
};
static void
fdstr_update_str1(struct fdstr *s)
{
fd = dup(fd);
if (fd < 0)
return false;
snprintf(s, FD_STR_LEN, "%d", fd);
return true;
snprintf(s->str1, sizeof(s->str1), "%d", s->fds[1]);
}
static void
fdstr_set_fd1(struct fdstr *s, int fd)
{
s->fds[0] = -1;
s->fds[1] = fd;
fdstr_update_str1(s);
}
static bool
fdstr_clear_cloexec_fd1(struct fdstr *s)
{
return os_fd_clear_cloexec(s->fds[1]) >= 0;
}
static void
fdstr_close_all(struct fdstr *s)
{
unsigned i;
for (i = 0; i < ARRAY_LENGTH(s->fds); i++) {
close(s->fds[i]);
s->fds[i] = -1;
}
}
static pid_t
@ -106,10 +130,11 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
{
struct wet_xwayland *wxw = user_data;
pid_t pid;
char wayland_socket_str[FD_STR_LEN], abstract_fd_str[FD_STR_LEN];
char unix_fd_str[FD_STR_LEN], wm_fd_str[FD_STR_LEN];
char display_fd_str[FD_STR_LEN];
int sv[2], wm[2], display_fd[2];
struct fdstr wayland_socket;
struct fdstr x11_abstract_socket;
struct fdstr x11_unix_socket;
struct fdstr x11_wm_socket;
struct fdstr display_pipe;
char *xserver = NULL;
struct weston_config *config = wet_get_config(wxw->compositor);
struct weston_config_section *section;
@ -117,31 +142,38 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
char *exec_failure_msg;
bool ret;
if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, sv) < 0) {
if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, wayland_socket.fds) < 0) {
weston_log("wl connection socketpair failed\n");
return 1;
}
fdstr_update_str1(&wayland_socket);
if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, wm) < 0) {
if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, x11_wm_socket.fds) < 0) {
weston_log("X wm connection socketpair failed\n");
return 1;
}
fdstr_update_str1(&x11_wm_socket);
if (pipe(display_fd) < 0) {
if (pipe(display_pipe.fds) < 0) {
weston_log("pipe creation for displayfd failed\n");
return 1;
}
if (os_fd_set_cloexec(display_fd[0]) != 0) {
if (os_fd_set_cloexec(display_pipe.fds[0]) != 0) {
weston_log("failed setting compositor end of displayfd as cloexec\n");
return 1;
}
if (os_fd_set_cloexec(display_fd[1]) != 0) {
if (os_fd_set_cloexec(display_pipe.fds[1]) != 0) {
weston_log("failed setting Xwayland end of displayfd as cloexec\n");
return 1;
}
fdstr_update_str1(&display_pipe);
fdstr_set_fd1(&x11_abstract_socket, abstract_fd);
fdstr_set_fd1(&x11_unix_socket, unix_fd);
section = weston_config_get_section(config, "xwayland", NULL, NULL);
weston_config_section_get_string(section, "path",
&xserver, XSERVER_PATH);
@ -151,27 +183,26 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
pid = fork();
switch (pid) {
case 0:
/* SOCK_CLOEXEC closes both ends, so we need to unset
* the flag on the client fd. */
ret = dup_fd_to_string(wayland_socket_str, sv[1]);
ret &= dup_fd_to_string(abstract_fd_str, abstract_fd);
ret &= dup_fd_to_string(unix_fd_str, unix_fd);
ret &= dup_fd_to_string(wm_fd_str, wm[1]);
ret &= dup_fd_to_string(display_fd_str, display_fd[1]);
ret = fdstr_clear_cloexec_fd1(&wayland_socket);
ret &= fdstr_clear_cloexec_fd1(&x11_abstract_socket);
ret &= fdstr_clear_cloexec_fd1(&x11_unix_socket);
ret &= fdstr_clear_cloexec_fd1(&x11_wm_socket);
ret &= fdstr_clear_cloexec_fd1(&display_pipe);
if (!ret)
_exit(EXIT_FAILURE);
setenv("WAYLAND_SOCKET", wayland_socket_str, 1);
setenv("WAYLAND_SOCKET", wayland_socket.str1, 1);
if (execl(xserver,
xserver,
display,
"-rootless",
LISTEN_STR, abstract_fd_str,
LISTEN_STR, unix_fd_str,
"-displayfd", display_fd_str,
"-wm", wm_fd_str,
LISTEN_STR, x11_abstract_socket.str1,
LISTEN_STR, x11_unix_socket.str1,
"-displayfd", display_pipe.str1,
"-wm", x11_wm_socket.str1,
"-terminate",
NULL) < 0) {
if (exec_failure_msg) {
@ -182,21 +213,23 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
_exit(EXIT_FAILURE);
default:
close(sv[1]);
wxw->client = wl_client_create(wxw->compositor->wl_display, sv[0]);
close(wayland_socket.fds[1]);
wxw->client = wl_client_create(wxw->compositor->wl_display,
wayland_socket.fds[0]);
close(wm[1]);
wxw->wm_fd = wm[0];
close(x11_wm_socket.fds[1]);
wxw->wm_fd = x11_wm_socket.fds[0];
/* During initialization the X server will round trip
* and block on the wayland compositor, so avoid making
* blocking requests (like xcb_connect_to_fd) until
* it's done with that. */
close(display_fd[1]);
close(display_pipe.fds[1]);
loop = wl_display_get_event_loop(wxw->compositor->wl_display);
wxw->display_fd_source =
wl_event_loop_add_fd(loop, display_fd[0], WL_EVENT_READABLE,
handle_display_fd, wxw);
wl_event_loop_add_fd(loop, display_pipe.fds[0],
WL_EVENT_READABLE,
handle_display_fd, wxw);
wxw->process.pid = pid;
wet_watch_process(wxw->compositor, &wxw->process);
@ -204,6 +237,9 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
case -1:
weston_log("Failed to fork to spawn xserver process\n");
fdstr_close_all(&wayland_socket);
fdstr_close_all(&x11_wm_socket);
fdstr_close_all(&display_pipe);
break;
}