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Support resolv_conf.head and resolv_conf.tail.

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These will be used if they exist at initialization.
Operations are all done by acting on pre-opened fds.
This commit is contained in:
Nicholas J. Kain 2016-05-06 06:41:15 -04:00
parent 313da14518
commit a47a2feea1
1 changed files with 70 additions and 13 deletions
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83
src/ifchd.c
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@ -60,6 +60,8 @@ static struct epoll_event events[2];
static int resolv_conf_fd = -1;
/* int ntp_conf_fd = -1; */
static int resolv_conf_head_fd = -1;
static int resolv_conf_tail_fd = -1;
/* If true, allow HOSTNAME changes from dhcp server. */
int allow_hostname = 0;
@ -75,6 +77,38 @@ static void writeordie(int fd, const char buf[static 1], size_t len)
__func__, r);
}
static int write_append_fd(int to_fd, int from_fd, const char descr[static 1])
{
if (from_fd < 0) return 0;
if (to_fd < 0) return -1;
const off_t lse = lseek(from_fd, 0, SEEK_END);
if (lse < 0) {
log_warning("%s: (%s) lseek(SEEK_END) failed %s",
client_config.interface, __func__, descr);
return -2;
}
if (lseek(from_fd, 0, SEEK_SET) < 0) {
log_warning("%s: (%s) lseek(SEEK_SET) failed %s",
client_config.interface, __func__, descr);
return -2;
}
char buf[4096];
size_t from_fd_len = lse;
while (from_fd_len > 0) {
const size_t to_read = from_fd_len <= sizeof buf ? from_fd_len : sizeof buf;
ssize_t r = safe_read(from_fd, buf, to_read);
if (r < 0 || (size_t)r != to_read)
suicide("%s: (%s) read failed %s", client_config.interface, __func__, descr);
r = safe_write(to_fd, buf, to_read);
if (r < 0 || (size_t)r != to_read)
suicide("%s: (%s) write failed %s", client_config.interface, __func__, descr);
from_fd_len -= to_read;
}
return 0;
}
/* Writes a new resolv.conf based on the information we have received. */
static int write_resolve_conf(void)
{
@ -92,6 +126,8 @@ static int write_resolve_conf(void)
if (lseek(resolv_conf_fd, 0, SEEK_SET) < 0)
return -1;
write_append_fd(resolv_conf_fd, resolv_conf_head_fd, "prepending resolv_conf head");
char *p = cl.namesvrs;
while (p && (*p != '\0')) {
char *q = strchr(p, ',');
@ -147,6 +183,8 @@ static int write_resolve_conf(void)
}
writeordie(resolv_conf_fd, "\n", 1);
write_append_fd(resolv_conf_fd, resolv_conf_tail_fd, "appending resolv_conf tail");
off = lseek(resolv_conf_fd, 0, SEEK_CUR);
if (off < 0) {
log_line("write_resolve_conf: lseek returned error: %s",
@ -345,24 +383,43 @@ static void do_ifch_work(void)
}
}
// If we are requested to update resolv.conf, preopen the fd before
// we drop root privileges, making sure that if we create
// resolv.conf, it will be world-readable.
static void setup_resolv_conf(void)
{
if (strncmp(resolv_conf_d, "", sizeof resolv_conf_d)) {
umask(022);
resolv_conf_fd = open(resolv_conf_d, O_RDWR|O_CREAT|O_CLOEXEC, 644);
umask(077);
if (resolv_conf_fd < 0) {
suicide("FATAL - unable to open resolv.conf");
}
char buf[PATH_MAX];
ssize_t sl = snprintf(buf, sizeof buf, "%s.head", resolv_conf_d);
if (sl < 0 || (size_t)sl >= sizeof buf)
log_warning("snprintf failed appending resolv_conf_head; path too long?");
else
resolv_conf_head_fd = open(buf, O_RDONLY|O_CLOEXEC, 0);
sl = snprintf(buf, sizeof buf, "%s.tail", resolv_conf_d);
if (sl < 0 || (size_t)sl >= sizeof buf)
log_warning("snprintf failed appending resolv_conf_tail; path too long?");
else
resolv_conf_tail_fd = open(buf, O_RDONLY|O_CLOEXEC, 0);
memset(buf, '\0', sizeof buf);
}
memset(resolv_conf_d, '\0', sizeof resolv_conf_d);
}
void ifch_main(void)
{
prctl(PR_SET_NAME, "ndhc: ifch");
umask(077);
signalFd = setup_signals_subprocess();
// If we are requested to update resolv.conf, preopen the fd before
// we drop root privileges, making sure that if we create
// resolv.conf, it will be world-readable.
if (strncmp(resolv_conf_d, "", sizeof resolv_conf_d)) {
umask(022);
resolv_conf_fd = open(resolv_conf_d, O_RDWR | O_CREAT, 644);
umask(077);
if (resolv_conf_fd < 0) {
suicide("FATAL - unable to open resolv.conf");
}
}
memset(resolv_conf_d, '\0', sizeof resolv_conf_d);
setup_resolv_conf();
nk_set_chroot(chroot_dir);
memset(chroot_dir, '\0', sizeof chroot_dir);