adb: Check sender's socket id when receiving packets.

handle_packet() in adb.c didn't check that when an A_WRTE packet is
received, the sender's local-id matches the socket's peer id.

This meant that a compromised adbd server could sent packets to
the host adb server, spoofing the identity of another connected
device if it could "guess" the right host socket id.

This patch gets rid of the issue by enforcing even more checks
to ensure that all packets comply with the description in
protocol.txt.

+ Fix a bug where closing a local socket associated with a
  remote one would always send an A_CLSE(0, remote-id, "")
  message, though protocol.txt says that should only happen
  for failed opens.

  The issue was that local_socket_close() called
  remote_socket_close() after clearing the remote socket's
  'peer' field.

  The fix introduces a new asocket optional callback,
  named 'shutdown' that is called before that, and is
  used to send the A_CLSE() message with the right ID
  in remote_socket_shutdown().

  Also add some code in handle_packet() to detect
  invalid close commands.

Change-Id: I9098bc8c6e81f8809334b060e5dca4fc92e6fbc9

1 files changed, 48 insertions, 9 deletions

diff --git a/adb/sockets.c b/adb/sockets.c
index f17608b..7f54ad9 100644
--- a/adb/sockets.c
+++ b/adb/sockets.c
@@ -59,17 +59,22 @@ static asocket local_socket_closing_list = {
     .prev = &local_socket_closing_list,
 };
 
-asocket *find_local_socket(unsigned id)
+// Parse the global list of sockets to find one with id |local_id|.
+// If |peer_id| is not 0, also check that it is connected to a peer
+// with id |peer_id|. Returns an asocket handle on success, NULL on failure.
+asocket *find_local_socket(unsigned local_id, unsigned peer_id)
 {
     asocket *s;
     asocket *result = NULL;
 
     adb_mutex_lock(&socket_list_lock);
     for (s = local_socket_list.next; s != &local_socket_list; s = s->next) {
-        if (s->id == id) {
+        if (s->id != local_id)
+            continue;
+        if (peer_id == 0 || (s->peer && s->peer->id == peer_id)) {
             result = s;
-            break;
         }
+        break;
     }
     adb_mutex_unlock(&socket_list_lock);
 
@@ -91,6 +96,11 @@ void install_local_socket(asocket *s)
     adb_mutex_lock(&socket_list_lock);
 
     s->id = local_socket_next_id++;
+
+    // Socket ids should never be 0.
+    if (local_socket_next_id == 0)
+      local_socket_next_id = 1;
+
     insert_local_socket(s, &local_socket_list);
 
     adb_mutex_unlock(&socket_list_lock);
@@ -230,6 +240,12 @@ static void local_socket_close_locked(asocket *s)
     if(s->peer) {
         D("LS(%d): closing peer. peer->id=%d peer->fd=%d\n",
           s->id, s->peer->id, s->peer->fd);
+        /* Note: it's important to call shutdown before disconnecting from
+         * the peer, this ensures that remote sockets can still get the id
+         * of the local socket they're connected to, to send a CLOSE()
+         * protocol event. */
+        if (s->peer->shutdown)
+          s->peer->shutdown(s->peer);
         s->peer->peer = 0;
         // tweak to avoid deadlock
         if (s->peer->close == local_socket_close) {
@@ -397,6 +413,7 @@ asocket *create_local_socket(int fd)
     s->fd = fd;
     s->enqueue = local_socket_enqueue;
     s->ready = local_socket_ready;
+    s->shutdown = NULL;
     s->close = local_socket_close;
     install_local_socket(s);
 
@@ -485,21 +502,29 @@ static void remote_socket_ready(asocket *s)
     send_packet(p, s->transport);
 }
 
-static void remote_socket_close(asocket *s)
+static void remote_socket_shutdown(asocket *s)
 {
-    D("entered remote_socket_close RS(%d) CLOSE fd=%d peer->fd=%d\n",
+    D("entered remote_socket_shutdown RS(%d) CLOSE fd=%d peer->fd=%d\n",
       s->id, s->fd, s->peer?s->peer->fd:-1);
     apacket *p = get_apacket();
     p->msg.command = A_CLSE;
     if(s->peer) {
         p->msg.arg0 = s->peer->id;
+    }
+    p->msg.arg1 = s->id;
+    send_packet(p, s->transport);
+}
+
+static void remote_socket_close(asocket *s)
+{
+    if (s->peer) {
         s->peer->peer = 0;
         D("RS(%d) peer->close()ing peer->id=%d peer->fd=%d\n",
           s->id, s->peer->id, s->peer->fd);
         s->peer->close(s->peer);
     }
-    p->msg.arg1 = s->id;
-    send_packet(p, s->transport);
+    D("entered remote_socket_close RS(%d) CLOSE fd=%d peer->fd=%d\n",
+      s->id, s->fd, s->peer?s->peer->fd:-1);
     D("RS(%d): closed\n", s->id);
     remove_transport_disconnect( s->transport, &((aremotesocket*)s)->disconnect );
     free(s);
@@ -519,15 +544,24 @@ static void remote_socket_disconnect(void*  _s, atransport*  t)
     free(s);
 }
 
+/* Create an asocket to exchange packets with a remote service through transport
+  |t|. Where |id| is the socket id of the corresponding service on the other
+   side of the transport (it is allocated by the remote side and _cannot_ be 0).
+   Returns a new non-NULL asocket handle. */
 asocket *create_remote_socket(unsigned id, atransport *t)
 {
-    asocket *s = calloc(1, sizeof(aremotesocket));
-    adisconnect*  dis = &((aremotesocket*)s)->disconnect;
+    asocket* s;
+    adisconnect* dis;
+
+    if (id == 0) fatal("invalid remote socket id (0)");
+    s = calloc(1, sizeof(aremotesocket));
+    dis = &((aremotesocket*)s)->disconnect;
 
     if (s == NULL) fatal("cannot allocate socket");
     s->id = id;
     s->enqueue = remote_socket_enqueue;
     s->ready = remote_socket_ready;
+    s->shutdown = remote_socket_shutdown;
     s->close = remote_socket_close;
     s->transport = t;
 
@@ -562,6 +596,7 @@ void connect_to_remote(asocket *s, const char *destination)
 static void local_socket_ready_notify(asocket *s)
 {
     s->ready = local_socket_ready;
+    s->shutdown = NULL;
     s->close = local_socket_close;
     adb_write(s->fd, "OKAY", 4);
     s->ready(s);
@@ -573,6 +608,7 @@ static void local_socket_ready_notify(asocket *s)
 static void local_socket_close_notify(asocket *s)
 {
     s->ready = local_socket_ready;
+    s->shutdown = NULL;
     s->close = local_socket_close;
     sendfailmsg(s->fd, "closed");
     s->close(s);
@@ -767,6 +803,7 @@ static int smart_socket_enqueue(asocket *s, apacket *p)
         adb_write(s->peer->fd, "OKAY", 4);
 
         s->peer->ready = local_socket_ready;
+        s->peer->shutdown = NULL;
         s->peer->close = local_socket_close;
         s->peer->peer = s2;
         s2->peer = s->peer;
@@ -806,6 +843,7 @@ static int smart_socket_enqueue(asocket *s, apacket *p)
         ** tear down
         */
     s->peer->ready = local_socket_ready_notify;
+    s->peer->shutdown = NULL;
     s->peer->close = local_socket_close_notify;
     s->peer->peer = 0;
         /* give him our transport and upref it */
@@ -851,6 +889,7 @@ static asocket *create_smart_socket(void)
     if (s == NULL) fatal("cannot allocate socket");
     s->enqueue = smart_socket_enqueue;
     s->ready = smart_socket_ready;
+    s->shutdown = NULL;
     s->close = smart_socket_close;
 
     D("SS(%d)\n", s->id);