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// SPDX-License-Identifier: AGPL-3.0-or-later
/* SEITAN - Syscall Expressive Interpreter, Transformer and Notifier
*
* seitan.c - Wait for processes, listen for syscalls, handle them
*
* Copyright (c) 2022 Red Hat GmbH
* Author: Stefano Brivio <sbrivio@redhat.com>
*/
#define _GNU_SOURCE
#include <errno.h>
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <limits.h>
#include <signal.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <linux/netlink.h>
#include <linux/connector.h>
#include <linux/cn_proc.h>
#include <linux/audit.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
static int nl_init(void)
{
int s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
struct sockaddr_nl sa = { .nl_family = AF_NETLINK,
.nl_groups = CN_IDX_PROC,
.nl_pid = getpid(),
};
struct req_t {
struct nlmsghdr nlh;
struct cn_msg cnm;
enum proc_cn_mcast_op mop;
} __attribute__ ((packed, aligned(NLMSG_ALIGNTO))) req = {
.nlh.nlmsg_type = NLMSG_DONE,
.nlh.nlmsg_pid = getpid(),
.cnm.id.idx = CN_IDX_PROC,
.cnm.id.val = CN_VAL_PROC,
.cnm.len = sizeof(enum proc_cn_mcast_op),
.mop = PROC_CN_MCAST_LISTEN,
};
bind(s, (struct sockaddr *)&sa, sizeof(sa));
req.nlh.nlmsg_len = sizeof(req);
send(s, &req, sizeof(req), 0);
return s;
}
static int event(int s)
{
char path[PATH_MAX + 1], exe[PATH_MAX + 1];
struct proc_event *ev;
struct nlmsghdr *nlh;
struct cn_msg *cnh;
char buf[BUFSIZ];
ssize_t n;
if ((n = recv(s, &buf, sizeof(buf), 0)) <= 0)
return -EIO;
nlh = (struct nlmsghdr *)buf;
for (; NLMSG_OK(nlh, n); nlh = NLMSG_NEXT(nlh, n)) {
if (nlh->nlmsg_type == NLMSG_NOOP)
continue;
if ((nlh->nlmsg_type == NLMSG_ERROR) ||
(nlh->nlmsg_type == NLMSG_OVERRUN))
break;
cnh = NLMSG_DATA(nlh);
ev = (struct proc_event *)cnh->data;
if (ev->what != PROC_EVENT_EXEC)
continue;
snprintf(path, PATH_MAX, "/proc/%i/exe",
ev->event_data.exec.process_pid);
readlink(path, exe, PATH_MAX);
if (!strcmp(exe, "/usr/local/bin/seitan-loader") ||
!strcmp(exe, "/usr/bin/seitan-loader"))
return ev->event_data.exec.process_pid;
if (nlh->nlmsg_type == NLMSG_DONE)
break;
}
return -EAGAIN;
}
enum transform {
NONE,
FD1_UNIX,
FDRET_SRC,
DEV_CHECK,
};
struct table {
enum transform type;
long number;
char arg[6][1024];
};
static struct table t[16];
int handle(struct seccomp_notif *req, int notifyfd)
{
char path[PATH_MAX + 1];
struct sockaddr_un s_un;
int fd_unix;
unsigned i;
int mem;
for (i = 0; i < sizeof(t) / sizeof(t[0]); i++) {
if (t[i].number == req->data.nr)
break;
}
if (i == sizeof(t) / sizeof(t[0])) /* Not found */
return 1;
if (t[i].type != FD1_UNIX) /* Not implemented yet */
return 1;
/* FD1_UNIX here */
snprintf(path, sizeof(path), "/proc/%i/mem", req->pid);
fd_unix = req->data.args[0];
mem = open(path, O_RDONLY);
lseek(mem, req->data.args[1], SEEK_SET);
read(mem, &s_un, sizeof(s_un));
close(mem);
if (!strcmp(s_un.sun_path, t[i].arg[0])) {
int own_fd = socket(AF_UNIX, SOCK_STREAM, 0);
struct seccomp_notif_addfd addfd = { .id = req->id,
.flags = SECCOMP_ADDFD_FLAG_SEND | SECCOMP_ADDFD_FLAG_SETFD,
.srcfd = own_fd, .newfd = fd_unix, };
connect(own_fd, &s_un, sizeof(s_un));
ioctl(notifyfd, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd);
return 0;
}
return 1;
}
int main(int argc, char **argv)
{
int s = nl_init(), ret, pidfd, notifier;
char resp_b[BUFSIZ], req_b[BUFSIZ];
struct seccomp_notif_resp *resp = (struct seccomp_notif_resp *)resp_b;
struct seccomp_notif *req = (struct seccomp_notif *)req_b;
int fd;
fd = open("t.out", O_CLOEXEC | O_RDONLY);
read(fd, t, sizeof(t));
close(fd);
if (argc < 2)
while ((ret = event(s)) == -EAGAIN);
else
ret = atoi(argv[1]);
if (ret < 0)
exit(EXIT_FAILURE);
if ((pidfd = syscall(SYS_pidfd_open, ret, 0)) < 0) {
perror("pidfd_open");
exit(EXIT_FAILURE);
}
sleep(1);
if ((notifier = syscall(SYS_pidfd_getfd, pidfd, 3, 0)) < 0) {
perror("pidfd_getfd");
exit(EXIT_FAILURE);
}
while (1) {
/* TODO: Open syscall transformation table blob, actually handle
* syscalls actions as parsed
*/
memset(req, 0, sizeof(*req));
ioctl(notifier, SECCOMP_IOCTL_NOTIF_RECV, req);
if (!handle(req, notifier))
continue;
resp->flags = SECCOMP_USER_NOTIF_FLAG_CONTINUE;
resp->id = req->id;
resp->error = 0;
resp->val = 0;
ioctl(notifier, SECCOMP_IOCTL_NOTIF_SEND, resp);
}
}
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