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0515adceaa
passt/passt.h
Stefano Brivio 0515adceaa passt, pasta: Namespace-based sandboxing, defer seccomp policy application 
To reach (at least) a conceptually equivalent security level as
implemented by --enable-sandbox in slirp4netns, we need to create a
new mount namespace and pivot_root() into a new (empty) mountpoint, so
that passt and pasta can't access any filesystem resource after
initialisation.

While at it, also detach IPC, PID (only for passt, to prevent
vulnerabilities based on the knowledge of a target PID), and UTS
namespaces.

With this approach, if we apply the seccomp filters right after the
configuration step, the number of allowed syscalls grows further. To
prevent this, defer the application of seccomp policies after the
initialisation phase, before the main loop, that's where we expect bad
things to happen, potentially. This way, we get back to 22 allowed
syscalls for passt and 34 for pasta, on x86_64.

While at it, move #syscalls notes to specific code paths wherever it
conceptually makes sense.

We have to open all the file handles we'll ever need before
sandboxing:

- the packet capture file can only be opened once, drop instance
  numbers from the default path and use the (pre-sandbox) PID instead

- /proc/net/tcp{,v6} and /proc/net/udp{,v6}, for automatic detection
  of bound ports in pasta mode, are now opened only once, before
  sandboxing, and their handles are stored in the execution context

- the UNIX domain socket for passt is also bound only once, before
  sandboxing: to reject clients after the first one, instead of
  closing the listening socket, keep it open, accept and immediately
  discard new connection if we already have a valid one

Clarify the (unchanged) behaviour for --netns-only in the man page.

To actually make passt and pasta processes run in a separate PID
namespace, we need to unshare(CLONE_NEWPID) before forking to
background (if configured to do so). Introduce a small daemon()
implementation, __daemon(), that additionally saves the PID file
before forking. While running in foreground, the process itself can't
move to a new PID namespace (a process can't change the notion of its
own PID): mention that in the man page.

For some reason, fork() in a detached PID namespace causes SIGTERM
and SIGQUIT to be ignored, even if the handler is still reported as
SIG_DFL: add a signal handler that just exits.

We can now drop most of the pasta_child_handler() implementation,
that took care of terminating all processes running in the same
namespace, if pasta started a shell: the shell itself is now the
init process in that namespace, and all children will terminate
once the init process exits.

Issuing 'echo $$' in a detached PID namespace won't return the
actual namespace PID as seen from the init namespace: adapt
demo and test setup scripts to reflect that.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
2022-02-21 13:41:13 +01:00

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/* SPDX-License-Identifier: AGPL-3.0-or-later
* Copyright (c) 2021 Red Hat GmbH
* Author: Stefano Brivio <sbrivio@redhat.com>
*/
#define UNIX_SOCK_MAX 100
#define UNIX_SOCK_PATH "/tmp/passt_%i.socket"
/**
* struct tap_msg - Generic message descriptor for arrays of messages
* @pkt_buf_offset: Offset from @pkt_buf
* @len: Message length, with L2 headers
*/
struct tap_msg {
uint32_t pkt_buf_offset;
uint16_t len;
};
/**
* struct tap_l4_msg - Layer-4 message descriptor for protocol handlers
* @pkt_buf_offset: Offset of message from @pkt_buf
* @l4_len: Length of Layer-4 payload, host order
*/
struct tap_l4_msg {
uint32_t pkt_buf_offset;
uint16_t l4_len;
};
union epoll_ref;
#include "icmp.h"
#include "tcp.h"
#include "udp.h"
/**
* union epoll_ref - Breakdown of reference for epoll socket bookkeeping
* @proto: IP protocol number
* @s: Socket number (implies 2^24 limit on number of descriptors)
* @tcp: TCP-specific reference part
* @udp: UDP-specific reference part
* @icmp: ICMP-specific reference part
* @data: Data handled by protocol handlers
* @u64: Opaque reference for epoll_ctl() and epoll_wait()
*/
union epoll_ref {
struct {
int32_t proto:8,
s:24;
union {
union tcp_epoll_ref tcp;
union udp_epoll_ref udp;
union icmp_epoll_ref icmp;
uint32_t data;
} p;
} r;
uint64_t u64;
};
#define TAP_BUF_BYTES \
ROUND_DOWN(((ETH_MAX_MTU + sizeof(uint32_t)) * 256), PAGE_SIZE)
#define TAP_BUF_FILL (TAP_BUF_BYTES - ETH_MAX_MTU - sizeof(uint32_t))
#define TAP_MSGS \
DIV_ROUND_UP(TAP_BUF_BYTES, ETH_ZLEN - 2 * ETH_ALEN + sizeof(uint32_t))
#define PKT_BUF_BYTES MAX(TAP_BUF_BYTES, 0)
extern char pkt_buf [PKT_BUF_BYTES];
extern char *ip_proto_str[];
#define IP_PROTO_STR(n) \
(((uint8_t)(n) <= IPPROTO_SCTP && ip_proto_str[(n)]) ? \
ip_proto_str[(n)] : "?")
#include <resolv.h> /* For MAXNS below */
/**
* struct fqdn - Representation of fully-qualified domain name
* @n: Domain name string
*/
struct fqdn {
char n[NS_MAXDNAME];
};
#include <net/if.h>
#include <linux/un.h>
enum passt_modes {
MODE_PASST,
MODE_PASTA,
};
/**
* struct ctx - Execution context
* @mode: Operation mode, qemu/UNIX domain socket or namespace/tap
* @debug: Enable debug mode
* @quiet: Don't print informational messages
* @foreground: Run in foreground, don't log to stderr by default
* @stderr: Force logging to stderr
* @sock_path: Path for UNIX domain socket
* @pcap: Path for packet capture file
* @pid_file: Path to PID file, empty string if not configured
* @pasta_netns_fd: File descriptor for network namespace in pasta mode
* @pasta_userns_fd: Descriptor for user namespace to join, -1 once joined
* @netns_only: In pasta mode, don't join or create a user namespace
* @proc_net_tcp: Stored handles for /proc/net/tcp{,6} in init and ns
* @proc_net_udp: Stored handles for /proc/net/udp{,6} in init and ns
* @epollfd: File descriptor for epoll instance
* @fd_tap_listen: File descriptor for listening AF_UNIX socket, if any
* @fd_tap: File descriptor for AF_UNIX socket or tuntap device
* @mac: Host MAC address
* @mac_guest: MAC address of guest or namespace, seen or configured
* @v4: Enable IPv4 transport
* @addr4: IPv4 address for external, routable interface
* @addr4_seen: Latest IPv4 address seen as source from tap
* @mask4: IPv4 netmask, network order
* @gw4: Default IPv4 gateway, network order
* @dns4: IPv4 DNS addresses, zero-terminated, network order
* @dns_search: DNS search list
* @v6: Enable IPv6 transport
* @addr6: IPv6 address for external, routable interface
* @addr6_ll: Link-local IPv6 address on external, routable interface
* @addr6_seen: Latest IPv6 global/site address seen as source from tap
* @addr6_ll_seen: Latest IPv6 link-local address seen as source from tap
* @gw6: Default IPv6 gateway
* @dns4: IPv4 DNS addresses, zero-terminated
* @ifi: Index of routable interface
* @pasta_ifn: Name of namespace interface for pasta
* @pasta_ifn: Index of namespace interface for pasta
* @pasta_conf_ns: Configure namespace interface after creating it
* @no_tcp: Disable TCP operation
* @tcp: Context for TCP protocol handler
* @no_tcp: Disable UDP operation
* @udp: Context for UDP protocol handler
* @no_icmp: Disable ICMP operation
* @icmp: Context for ICMP protocol handler
* @mtu: MTU passed via DHCP/NDP
* @no_dns: Do not assign any DNS server via DHCP/DHCPv6/NDP
* @no_dns_search: Do not assign any DNS domain search via DHCP/DHCPv6/NDP
* @no_dhcp: Disable DHCP server
* @no_dhcpv6: Disable DHCPv6 server
* @no_ndp: Disable NDP handler altogether
* @no_ra: Disable router advertisements
* @no_map_gw: Don't map connections, untracked UDP to gateway to host
* @low_wmem: Low probed net.core.wmem_max
* @low_rmem: Low probed net.core.rmem_max
*/
struct ctx {
enum passt_modes mode;
int debug;
int quiet;
int foreground;
int stderr;
char sock_path[UNIX_PATH_MAX];
char pcap[PATH_MAX];
char pid_file[PATH_MAX];
int pasta_netns_fd;
int pasta_userns_fd;
int netns_only;
int proc_net_tcp[IP_VERSIONS][2];
int proc_net_udp[IP_VERSIONS][2];
int epollfd;
int fd_tap_listen;
int fd_tap;
unsigned char mac[ETH_ALEN];
unsigned char mac_guest[ETH_ALEN];
int v4;
uint32_t addr4;
uint32_t addr4_seen;
uint32_t mask4;
uint32_t gw4;
uint32_t dns4[MAXNS + 1];
struct fqdn dns_search[MAXDNSRCH];
int v6;
struct in6_addr addr6;
struct in6_addr addr6_ll;
struct in6_addr addr6_seen;
struct in6_addr addr6_ll_seen;
struct in6_addr gw6;
struct in6_addr dns6[MAXNS + 1];
unsigned int ifi;
char pasta_ifn[IF_NAMESIZE];
unsigned int pasta_ifi;
int pasta_conf_ns;
int no_tcp;
struct tcp_ctx tcp;
int no_udp;
struct udp_ctx udp;
int no_icmp;
struct icmp_ctx icmp;
int mtu;
int no_dns;
int no_dns_search;
int no_dhcp;
int no_dhcpv6;
int no_ndp;
int no_ra;
int no_map_gw;
int low_wmem;
int low_rmem;
};
void proto_update_l2_buf(unsigned char *eth_d, unsigned char *eth_s,
uint32_t *ip_da);
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