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| | // SPDX-License-Identifier: GPL-2.0-or-later
/* PASST - Plug A Simple Socket Transport
* for qemu/UNIX domain socket mode
*
* PASTA - Pack A Subtle Tap Abstraction
* for network namespace/tap device mode
*
* passt-repair.c - Privileged helper to set/clear TCP_REPAIR on sockets
*
* Copyright (c) 2025 Red Hat GmbH
* Author: Stefano Brivio <sbrivio@redhat.com>
*
* Connect to passt via UNIX domain socket, receive sockets via SCM_RIGHTS along
* with byte commands mapping to TCP_REPAIR values, and switch repair mode on or
* off. Reply by echoing the command. Exit on EOF.
*/
#include <sys/prctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/tcp.h>
#include <linux/audit.h>
#include <linux/capability.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include "seccomp_repair.h"
#define SCM_MAX_FD 253 /* From Linux kernel (include/net/scm.h), not in UAPI */
/**
* main() - Entry point and whole program with loop
* @argc: Argument count, must be 2
* @argv: Argument: path of UNIX domain socket to connect to
*
* Return: 0 on success (EOF), 1 on error, 2 on usage error
*
* #syscalls:repair connect setsockopt write close exit_group
* #syscalls:repair socket s390x:socketcall i686:socketcall
* #syscalls:repair recvfrom recvmsg arm:recv ppc64le:recv
* #syscalls:repair sendto sendmsg arm:send ppc64le:send
*/
int main(int argc, char **argv)
{
char buf[CMSG_SPACE(sizeof(int) * SCM_MAX_FD)]
__attribute__ ((aligned(__alignof__(struct cmsghdr))));
struct sockaddr_un a = { AF_UNIX, "" };
int fds[SCM_MAX_FD], s, ret, i, n = 0;
struct sock_fprog prog;
int8_t cmd = INT8_MAX;
struct cmsghdr *cmsg;
struct msghdr msg;
struct iovec iov;
int op;
prctl(PR_SET_DUMPABLE, 0);
prog.len = (unsigned short)sizeof(filter_repair) /
sizeof(filter_repair[0]);
prog.filter = filter_repair;
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
fprintf(stderr, "Failed to apply seccomp filter");
_exit(1);
}
iov = (struct iovec){ &cmd, sizeof(cmd) };
msg = (struct msghdr){ .msg_name = NULL, .msg_namelen = 0,
.msg_iov = &iov, .msg_iovlen = 1,
.msg_control = buf,
.msg_controllen = sizeof(buf),
.msg_flags = 0 };
cmsg = CMSG_FIRSTHDR(&msg);
if (argc != 2) {
fprintf(stderr, "Usage: %s PATH\n", argv[0]);
_exit(2);
}
ret = snprintf(a.sun_path, sizeof(a.sun_path), "%s", argv[1]);
if (ret <= 0 || ret >= (int)sizeof(a.sun_path)) {
fprintf(stderr, "Invalid socket path: %s\n", argv[1]);
_exit(2);
}
if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
fprintf(stderr, "Failed to create AF_UNIX socket: %i\n", errno);
_exit(1);
}
if (connect(s, (struct sockaddr *)&a, sizeof(a))) {
fprintf(stderr, "Failed to connect to %s: %s\n", argv[1],
strerror(errno));
_exit(1);
}
loop:
ret = recvmsg(s, &msg, 0);
if (ret < 0) {
if (errno == ECONNRESET) {
ret = 0;
} else {
fprintf(stderr, "Failed to read message: %i\n", errno);
_exit(1);
}
}
if (!ret) /* Done */
_exit(0);
if (!cmsg ||
cmsg->cmsg_len < CMSG_LEN(sizeof(int)) ||
cmsg->cmsg_len > CMSG_LEN(sizeof(int) * SCM_MAX_FD) ||
cmsg->cmsg_type != SCM_RIGHTS) {
fprintf(stderr, "No/bad ancillary data from peer\n");
_exit(1);
}
/* No inverse formula for CMSG_LEN(x), and building one with CMSG_LEN(0)
* works but there's no guarantee it does. Search the whole domain.
*/
for (i = 1; i < SCM_MAX_FD; i++) {
if (CMSG_LEN(sizeof(int) * i) == cmsg->cmsg_len) {
n = i;
break;
}
}
if (!n) {
fprintf(stderr, "Invalid ancillary data length %zu from peer\n",
cmsg->cmsg_len);
_exit(1);
}
memcpy(fds, CMSG_DATA(cmsg), sizeof(int) * n);
if (cmd != TCP_REPAIR_ON && cmd != TCP_REPAIR_OFF &&
cmd != TCP_REPAIR_OFF_NO_WP) {
fprintf(stderr, "Unsupported command 0x%04x\n", cmd);
_exit(1);
}
op = cmd;
for (i = 0; i < n; i++) {
if (setsockopt(fds[i], SOL_TCP, TCP_REPAIR, &op, sizeof(op))) {
fprintf(stderr,
"Setting TCP_REPAIR to %i on socket %i: %s", op,
fds[i], strerror(errno));
_exit(1);
}
/* Close _our_ copy */
close(fds[i]);
}
/* Confirm setting by echoing the command back */
if (send(s, &cmd, sizeof(cmd), 0) < 0) {
fprintf(stderr, "Reply to %i: %s\n", op, strerror(errno));
_exit(1);
}
goto loop;
return 0;
}
|