Allow to intercept more kernel connections (#513)

* Allow to intercept some kernel connections

Some connections are initiated from kernel space, like WireGuard
VPNs (#454), NFS or SMB connections (#502) and ip tunnels (#500).

Note: This feature is complete for x86_64, WIP for aarch64, and not supported for armhf and i386
https://github.com/evilsocket/opensnitch/pull/513#issuecomment-924400824

More information regarding this change: #493

daemon/procmon/details.go

@@ -36,6 +36,15 @@ func (p *Process) setCwd(cwd string) {
 	p.CWD = cwd
 }
 
+func (p *Process) readComm() error {
+	data, err := ioutil.ReadFile(fmt.Sprintf("/proc/%d/comm", p.ID))
+	if err != nil {
+		return err
+	}
+	p.Comm = core.Trim(string(data))
+	return nil
+}
+
 func (p *Process) readCwd() error {
 	link, err := os.Readlink(fmt.Sprintf("/proc/%d/cwd", p.ID))
 	if err != nil {
@@ -74,6 +83,9 @@ func (p *Process) readPath() error {
 
 func (p *Process) readCmdline() {
 	if data, err := ioutil.ReadFile(fmt.Sprintf("/proc/%d/cmdline", p.ID)); err == nil {
+		if len(data) == 0 {
+			return
+		}
 		for i, b := range data {
 			if b == 0x00 {
 				data[i] = byte(' ')

daemon/procmon/parse.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"time"
 
+	"github.com/evilsocket/opensnitch/daemon/core"
 	"github.com/evilsocket/opensnitch/daemon/log"
 	"github.com/evilsocket/opensnitch/daemon/procmon/audit"
 )
@@ -86,9 +87,6 @@ func GetPIDFromINode(inode int, inodeKey string) int {
 // If it exists in /proc, a new Process{} object is returned with  the details
 // to identify a process (cmdline, name, environment variables, etc).
 func FindProcess(pid int, interceptUnknown bool) *Process {
-	if interceptUnknown && pid == -100 {
-		return NewProcess(-100, "Linux kernel")
-	}
 	if interceptUnknown && pid < 0 {
 		return NewProcess(0, "")
 	}
@@ -115,22 +113,32 @@ func FindProcess(pid int, interceptUnknown bool) *Process {
 			return proc
 		}
 	}
-
-	linkName := fmt.Sprint("/proc/", pid, "/exe")
-	if _, err := os.Lstat(linkName); err != nil {
+	// if the PID dir doesn't exist, the process may have exited or be a kernel connection
+	// XXX: can a kernel connection exist without an entry in ProcFS?
+	if core.Exists(fmt.Sprint("/proc/", pid)) == false {
+		log.Debug("PID can't be read /proc/", pid)
 		return nil
 	}
 
-	if link, err := os.Readlink(linkName); err == nil {
-		proc := NewProcess(pid, link)
+	linkName := fmt.Sprint("/proc/", pid, "/exe")
+	link, err := os.Readlink(linkName)
+	proc := NewProcess(pid, link)
+	proc.readCmdline()
+	proc.readCwd()
+	proc.readEnv()
+	proc.cleanPath()
 
-		proc.readCmdline()
-		proc.readCwd()
-		proc.readEnv()
-		proc.cleanPath()
-
-		addToActivePidsCache(uint64(pid), proc)
-		return proc
+	if len(proc.Args) == 0 {
+		proc.readComm()
+		proc.Args = make([]string, 0)
+		proc.Args = append(proc.Args, proc.Comm)
 	}
-	return nil
+
+	// If the link to the binary can't be read, the PID may be of a kernel task
+	if err != nil || proc.Path == "" {
+		proc.Path = "Kernel connection"
+	}
+
+	addToActivePidsCache(uint64(pid), proc)
+	return proc
 }

daemon/procmon/process.go

@@ -46,6 +46,7 @@ type procStatm struct {
 // Process holds the details of a process.
 type Process struct {
 	ID          int
+	Comm        string
 	Path        string
 	Args        []string
 	Env         map[string]string

ebpf_prog/opensnitch.c

@@ -3,12 +3,15 @@
 //uncomment if building on x86_32
 //#define OPENSNITCH_x86_32
 
+#include <linux/sched.h>
 #include <linux/ptrace.h>
 #include <linux/version.h>
 #include <uapi/linux/bpf.h>
+#include <uapi/linux/tcp.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h> 
 #include <net/sock.h>
+#include <net/udp_tunnel.h>
 #include <net/inet_sock.h>
 
 #define MAPSIZE 12000
@@ -97,6 +100,7 @@ struct udpv6_value_t{
 	u64 counter;
 }__attribute__((packed));
 
+
 // on x86_32 "struct sock" is arranged differently from x86_64 (at least on Debian kernels).
 // We hardcode offsets of IP addresses.
 struct sock_on_x86_32_t {
@@ -224,7 +228,6 @@ int kprobe__tcp_v4_connect(struct pt_regs *ctx)
 	return 0;
 };
 
-
 SEC("kretprobe/tcp_v4_connect")
 int kretprobe__tcp_v4_connect(struct pt_regs *ctx)
 {
@@ -253,6 +256,7 @@ int kretprobe__tcp_v4_connect(struct pt_regs *ctx)
 	tcp_value.uid = bpf_get_current_uid_gid() & 0xffffffff;
 	tcp_value.counter = *val;
 	bpf_map_update_elem(&tcpMap, &tcp_key, &tcp_value, BPF_ANY);
+
 	u64 newval = *val + 1;
 	bpf_map_update_elem(&tcpcounter, &zero_key, &newval, BPF_ANY);
 	bpf_map_delete_elem(&tcpsock, &pid_tgid);
@@ -274,6 +278,7 @@ int kprobe__tcp_v6_connect(struct pt_regs *ctx)
 	bpf_map_update_elem(&tcpv6sock, &pid_tgid, &skp, BPF_ANY);
 	return 0;
 };
+
 SEC("kretprobe/tcp_v6_connect")
 int kretprobe__tcp_v6_connect(struct pt_regs *ctx)
 {
@@ -309,6 +314,7 @@ int kretprobe__tcp_v6_connect(struct pt_regs *ctx)
 	tcpv6_value.uid = bpf_get_current_uid_gid() & 0xffffffff;
 	tcpv6_value.counter = *val;
 	bpf_map_update_elem(&tcpv6Map, &tcpv6_key, &tcpv6_value, BPF_ANY);
+
 	u64 newval = *val + 1;
 	bpf_map_update_elem(&tcpv6counter, &zero_key, &newval, BPF_ANY);
 	bpf_map_delete_elem(&tcpv6sock, &pid_tgid);
@@ -359,6 +365,7 @@ int kprobe__udp_sendmsg(struct pt_regs *ctx)
 		udp_value.uid = bpf_get_current_uid_gid() & 0xffffffff;
 		udp_value.counter = *counterVal;
 		bpf_map_update_elem(&udpMap, &udp_key, &udp_value, BPF_ANY);
+
 		u64 newval = *counterVal + 1;
 		bpf_map_update_elem(&udpcounter, &zero_key, &newval, BPF_ANY);
 	}
@@ -427,6 +434,61 @@ int kprobe__udpv6_sendmsg(struct pt_regs *ctx)
 	
 };
 
+SEC("kprobe/iptunnel_xmit")
+int kprobe__iptunnel_xmit(struct pt_regs *ctx)
+{
+	#ifdef OPENSNITCH_x86_32
+	// TODO
+	return 0;
+	#else
+		struct sk_buff *skb = (struct sk_buff *)PT_REGS_PARM3(ctx);
+		u32 src = (u32)PT_REGS_PARM4(ctx);
+		u32 dst = (u32)PT_REGS_PARM5(ctx);
+	#endif
+
+	u16 sport = 0;
+	unsigned char *head;
+	u16 pkt_hdr;
+	__builtin_memset(&head, 0, sizeof(head));
+	__builtin_memset(&pkt_hdr, 0, sizeof(pkt_hdr));
+	bpf_probe_read(&head, sizeof(head), &skb->head);
+	bpf_probe_read(&pkt_hdr, sizeof(pkt_hdr), &skb->transport_header);
+	struct udphdr *udph;
+	__builtin_memset(&udph, 0, sizeof(udph));
+
+	udph = (struct udphdr *)(head + pkt_hdr);
+	bpf_probe_read(&sport, sizeof(sport), &udph->source);
+	sport = (sport >> 8) | ((sport << 8) & 0xff00);
+
+	struct udp_key_t udp_key;
+	struct udp_value_t udp_value;
+	u32 zero_key = 0;
+	__builtin_memset(&udp_key, 0, sizeof(udp_key));
+	__builtin_memset(&udp_value, 0, sizeof(udp_value));
+
+	bpf_probe_read(&udp_key.sport, sizeof(udp_key.sport), &sport);
+	bpf_probe_read(&udp_key.dport, sizeof(udp_key.dport), &udph->dest);
+	bpf_probe_read(&udp_key.saddr, sizeof(udp_key.saddr), &src);
+	bpf_probe_read(&udp_key.daddr, sizeof(udp_key.daddr), &dst);
+
+	u64 *counterVal = bpf_map_lookup_elem(&udpcounter, &zero_key);
+	if (counterVal == NULL){return 0;}
+
+	struct udp_value_t *lookedupValue = bpf_map_lookup_elem(&udpMap, &udp_key);
+	u64 pid = bpf_get_current_pid_tgid() >> 32;
+	if ( lookedupValue == NULL || lookedupValue->pid != pid) {
+		udp_value.pid = pid;
+		udp_value.uid = bpf_get_current_uid_gid() & 0xffffffff;
+		udp_value.counter = *counterVal;
+		bpf_map_update_elem(&udpMap, &udp_key, &udp_value, BPF_ANY);
+		u64 newval = *counterVal + 1;
+		bpf_map_update_elem(&udpcounter, &zero_key, &newval, BPF_ANY);
+	}
+
+	return 0;
+
+};
+
 // debug only: increment key's value by 1 in map "bytes"
 void increment(u32 key){
 	u32 *lookedupValue = bpf_map_lookup_elem(&bytes, &key);