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xwayland: do not use setenv() after fork() 

Between fork() and exec() in the child process it is only safe to use
async-signal-safe functions. Painfully, setenv() is not listed as such.

Therefore we must craft our own custom environment, and we get no help
from libc with that.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This commit is contained in:
Pekka Paalanen 2022-07-07 15:41:48 +03:00 committed by Pekka Paalanen
parent d1b01ffb9a
commit 1bd92dac01
1 changed files with 92 additions and 3 deletions
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95
compositor/xwayland.c
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@ -126,6 +126,91 @@ fdstr_close_all(struct fdstr *s)
}
}
struct custom_env {
struct wl_array p;
bool finalized;
};
static void
custom_env_init_from_environ(struct custom_env *env)
{
char **it;
char **ep;
wl_array_init(&env->p);
env->finalized = false;
for (it = environ; *it; it++) {
ep = wl_array_add(&env->p, sizeof *ep);
assert(ep);
*ep = strdup(*it);
assert(*ep);
}
}
static void
custom_env_fini(struct custom_env *env)
{
char **ep;
wl_array_for_each(ep, &env->p)
free(*ep);
wl_array_release(&env->p);
}
static char **
custom_env_find_element(struct custom_env *env, const char *name)
{
char **ep;
size_t name_len = strlen(name);
wl_array_for_each(ep, &env->p) {
char *entry = *ep;
if (strncmp(entry, name, name_len) == 0 &&
entry[name_len] == '=') {
return ep;
}
}
return NULL;
}
static void
custom_env_set(struct custom_env *env, const char *name, const char *value)
{
char **ep;
assert(strchr(name, '=') == NULL);
assert(!env->finalized);
ep = custom_env_find_element(env, name);
if (ep)
free(*ep);
else
ep = wl_array_add(&env->p, sizeof *ep);
assert(ep);
str_printf(ep, "%s=%s", name, value);
assert(*ep);
}
static char *const *
custom_env_get_envp(struct custom_env *env)
{
char **ep;
/* add terminating NULL */
ep = wl_array_add(&env->p, sizeof *ep);
assert(ep);
*ep = NULL;
env->finalized = true;
return env->p.data;
}
static pid_t
spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd)
{
@ -141,6 +226,8 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
struct weston_config_section *section;
struct wl_event_loop *loop;
char *exec_failure_msg;
struct custom_env child_env;
char *const *envp;
bool ret;
if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, wayland_socket.fds) < 0) {
@ -169,6 +256,9 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
&xserver, XSERVER_PATH);
str_printf(&exec_failure_msg,
"Error: executing Xwayland as '%s' failed.\n", xserver);
custom_env_init_from_environ(&child_env);
custom_env_set(&child_env, "WAYLAND_SOCKET", wayland_socket.str1);
envp = custom_env_get_envp(&child_env);
const char *const argv[] = {
xserver,
@ -195,9 +285,7 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
if (!ret)
_exit(EXIT_FAILURE);
setenv("WAYLAND_SOCKET", wayland_socket.str1, 1);
if (execv(xserver, (char *const *)argv) < 0) {
if (execve(xserver, (char *const *)argv, envp) < 0) {
if (exec_failure_msg) {
write(STDERR_FILENO, exec_failure_msg,
strlen(exec_failure_msg));
@ -237,6 +325,7 @@ spawn_xserver(void *user_data, const char *display, int abstract_fd, int unix_fd
break;
}
custom_env_fini(&child_env);
free(exec_failure_msg);
free(xserver);