Parse local address from socket info if remote addr is known (#1833)

Summary: Add condition before `InferConnInfo` to parse the local address
from socket information if missing when the remote address is known.
Note that this most likely occurs for syscalls (i.e. `connect`) for
which we are currently unable to trace the local IP using socket
information [from
bpf](https://github.com/pixie-io/pixie/blob/561ec31a619e9265cfae319a0aa7ec36e19e29d2/src/stirling/source_connectors/socket_tracer/bcc_bpf/socket_trace.c#L632).

Type of change: /kind feature

Test Plan: Existing E2E tests. Skaffolded to a cluster with kafka and
redis demos deployed and inspected pem logs (added logs to print
successfully inferred local IPs when remote IP is present). Ran
standalone pem on a node with kafka/redis demos running and inspected
logs.

Note that I've opted for an E2E test because writing a test case that
reliably reproduces the conditions for inference has been tricky. We'd
need to ensure that

1. remote address is known while local IP is not
2. short-lived processes/sockets don’t terminate or close before we
check `/proc/[pid]/fd/[n]`
3. connections are not bound to the loopback network interface

---------

Signed-off-by: Benjamin Kilimnik <[email protected]>

src/stirling/source_connectors/socket_tracer/conn_tracker.cc

@@ -797,9 +797,12 @@ void ConnTracker::IterationPreTick(
 
   // If remote_addr is missing, it means the connect/accept syscall was not traced.
   // Attempt to infer the connection information, to populate remote_addr and local_addr.
-  if (open_info_.remote_addr.family == SockAddrFamily::kUnspecified && socket_info_mgr != nullptr) {
-    InferConnInfo(proc_parser, socket_info_mgr);
+  const bool raddr_found = open_info_.remote_addr.family != SockAddrFamily::kUnspecified;
+  const bool laddr_found = open_info_.local_addr.family != SockAddrFamily::kUnspecified;
+  const bool info_mgr_ok = socket_info_mgr != nullptr;
 
+  if ((!raddr_found || !laddr_found) && info_mgr_ok) {
+    InferConnInfo(proc_parser, socket_info_mgr);
     // TODO(oazizi): If connection resolves to SockAddr type "Other",
     //               we should mark the state in BPF to Other too, so BPF stops tracing.
     //               We should also mark the ConnTracker for death.
@@ -901,24 +904,17 @@ double ConnTracker::StitchFailureRate() const {
 
 namespace {
 
-Status ParseSocketInfoAddr(const system::SocketInfo& socket_info, SockAddr* remote_addr,
-                           SockAddr* local_addr) {
+Status ParseSocketInfoLocalAddr(const system::SocketInfo& socket_info, SockAddr* local_addr) {
   switch (socket_info.family) {
     case AF_INET:
-      PopulateInetAddr(std::get<struct in_addr>(socket_info.remote_addr), socket_info.remote_port,
-                       remote_addr);
       PopulateInetAddr(std::get<struct in_addr>(socket_info.local_addr), socket_info.local_port,
                        local_addr);
       break;
     case AF_INET6:
-      PopulateInet6Addr(std::get<struct in6_addr>(socket_info.remote_addr), socket_info.remote_port,
-                        remote_addr);
       PopulateInet6Addr(std::get<struct in6_addr>(socket_info.local_addr), socket_info.local_port,
                         local_addr);
       break;
     case AF_UNIX:
-      PopulateUnixAddr(std::get<struct un_path_t>(socket_info.remote_addr).path,
-                       socket_info.remote_port, remote_addr);
       PopulateUnixAddr(std::get<struct un_path_t>(socket_info.local_addr).path,
                        socket_info.local_port, local_addr);
       break;
@@ -929,6 +925,27 @@ Status ParseSocketInfoAddr(const system::SocketInfo& socket_info, SockAddr* remo
   return Status::OK();
 }
 
+Status ParseSocketInfoRemoteAddr(const system::SocketInfo& socket_info, SockAddr* remote_addr) {
+  switch (socket_info.family) {
+    case AF_INET:
+      PopulateInetAddr(std::get<struct in_addr>(socket_info.remote_addr), socket_info.remote_port,
+                       remote_addr);
+      break;
+    case AF_INET6:
+      PopulateInet6Addr(std::get<struct in6_addr>(socket_info.remote_addr), socket_info.remote_port,
+                        remote_addr);
+      break;
+    case AF_UNIX:
+      PopulateUnixAddr(std::get<struct un_path_t>(socket_info.remote_addr).path,
+                       socket_info.remote_port, remote_addr);
+      break;
+    default:
+      return error::Internal("Unknown socket_info family: $0", socket_info.family);
+  }
+
+  return Status::OK();
+}
+
 endpoint_role_t TranslateRole(system::ClientServerRole role) {
   switch (role) {
     case system::ClientServerRole::kClient:
@@ -949,6 +966,9 @@ void ConnTracker::InferConnInfo(system::ProcParser* proc_parser,
   DCHECK(proc_parser != nullptr);
   DCHECK(socket_info_mgr != nullptr);
 
+  const bool raddr_found = open_info_.remote_addr.family != SockAddrFamily::kUnspecified;
+  const bool laddr_found = open_info_.local_addr.family != SockAddrFamily::kUnspecified;
+
   if (conn_resolution_failed_) {
     // We've previously tried and failed to perform connection inference,
     // so don't waste any time...a connection only gets one chance.
@@ -962,7 +982,9 @@ void ConnTracker::InferConnInfo(system::ProcParser* proc_parser,
     bool success = conn_resolver_->Setup();
     if (!success) {
       conn_resolver_.reset();
-      conn_resolution_failed_ = true;
+      if (!raddr_found) {
+        conn_resolution_failed_ = true;
+      }
       CONN_TRACE(2) << "Can't infer remote endpoint. Setup failed.";
     } else {
       CONN_TRACE(2) << "FDResolver has been created.";
@@ -1024,13 +1046,22 @@ void ConnTracker::InferConnInfo(system::ProcParser* proc_parser,
 
   // Success! Now copy the inferred socket information into the ConnTracker.
 
-  Status s = ParseSocketInfoAddr(socket_info, &open_info_.remote_addr, &open_info_.local_addr);
-  if (!s.ok()) {
-    conn_resolver_.reset();
-    conn_resolution_failed_ = true;
-    LOG(ERROR) << absl::Substitute("Remote and local address (type=$0) parsing failed. Message: $1",
-                                   socket_info.family, s.msg());
-    return;
+  if (!laddr_found) {
+    Status s = ParseSocketInfoLocalAddr(socket_info, &open_info_.local_addr);
+    if (!s.ok()) {
+      CONN_TRACE(2) << absl::Substitute("Local address (type=$0) parsing failed. Message: $1",
+                                        socket_info.family, s.msg());
+    }
+  }
+  if (!raddr_found) {
+    Status s = ParseSocketInfoRemoteAddr(socket_info, &open_info_.remote_addr);
+    if (!s.ok()) {
+      conn_resolver_.reset();
+      conn_resolution_failed_ = true;
+      CONN_TRACE(2) << absl::Substitute("Remote address (type=$0) parsing failed. Message: $1",
+                                        socket_info.family, s.msg());
+      return;
+    }
   }
 
   endpoint_role_t inferred_role = TranslateRole(socket_info.role);