Attempt to make data saver mode work for real.

The data saver refactoring change was incorrect in >= two ways:

1. It relied on the bw_costly_shared chain, which is currently
   unused. NetworkManagementService just has a "TODO: support
   quota shared across interfaces" comment about it. What
   actually happens when setting quota is that each costly
   interface chain (e.g., bw_costly_rmnet_data0) directly hooks
   in the bw_penalty box chain.

2. Implementing app whitelisting using "RETURN" inside
   bw_happy_box was pointless because if data saver was enabled,
   there was a REJECT at the end of the bw_costly_shared chain
   that it was returning to.

Instead, go back to the previous approach which hooked
bw_happy_box at the end of bw_penalty_box. Also, add an
additional bw_data_saver rule at the end of bw_happy_box.
bw_data_saver only contains one rule: RETURN if data saver is
enabled or REJECT if data saver is disabled.

That way:

1. If the app is blacklisted, bw_penalty_box REJECTs. If not:
2. If the app is whitelisted (system apps are always whitelisted)
   bw_happy_box RETURNs to bw_costly_rmnet_data0, skipping
   bw_data_saver.
3. If an app is neither blacklisted nor whitelisted, bw_happy_box
   jumps to bw_data_saver. If data saver is enabled, it REJECTs
   the packet, and if not, it RETURNs to bw_costly_rmnet_data0.
4. When we RETURN to bw_costly_rmnet_data0, either because the
   app is whitelisted, or because data saver is off,
   bw_costly_rmnet_data0 applies mobile data usage limits,
   and then RETURNs to bw_OUTPUT, which calls xt_qtaguid, etc.

Bug: 26685616
Bug: 27506285
Change-Id: If15397afde6862d95827a1fdd30f60efd7fab66a

1 files changed, 8 insertions, 6 deletions

diff --git a/server/BandwidthControllerTest.cpp b/server/BandwidthControllerTest.cpp
index 4a59883a..82518302 100644
--- a/server/BandwidthControllerTest.cpp
+++ b/server/BandwidthControllerTest.cpp
@@ -26,7 +26,7 @@
 
 std::vector<std::string> gCmds = {};
 
-extern "C" int fake_android_fork_exec(int argc, char* argv[], int *status, bool, bool) {
+int fake_android_fork_exec(int argc, char* argv[], int *status, bool, bool) {
     std::string cmd = argv[0];
     for (int i = 1; i < argc; i++) {
         cmd += " ";
@@ -72,6 +72,7 @@ TEST_F(BandwidthControllerTest, TestEnableBandwidthControl) {
         "-F bw_FORWARD",
         "-F bw_happy_box",
         "-F bw_penalty_box",
+        "-F bw_data_saver",
         "-F bw_costly_shared",
         "-t raw -F bw_raw_PREROUTING",
         "-t mangle -F bw_mangle_POSTROUTING",
@@ -80,9 +81,10 @@ TEST_F(BandwidthControllerTest, TestEnableBandwidthControl) {
         "-t raw -A bw_raw_PREROUTING -m owner --socket-exists",
         "-t mangle -A bw_mangle_POSTROUTING -m owner --socket-exists",
         "-A bw_costly_shared --jump bw_penalty_box",
-        "-A bw_costly_shared --jump bw_happy_box",
-        "-A bw_costly_shared --jump RETURN",
-        "-A bw_happy_box -m owner --uid-owner 0-9999 --jump RETURN",
+        "-A bw_penalty_box --jump bw_happy_box",
+        "-A bw_happy_box --jump bw_data_saver",
+        "-A bw_data_saver -j RETURN",
+        "-I bw_happy_box -m owner --uid-owner 0-9999 --jump RETURN",
     };
     expectIptablesCommands(expected);
 }
@@ -90,13 +92,13 @@ TEST_F(BandwidthControllerTest, TestEnableBandwidthControl) {
 TEST_F(BandwidthControllerTest, TestEnableDataSaver) {
     mBw.enableDataSaver(true);
     std::vector<std::string> expected = {
-        "-R bw_costly_shared 3 --jump REJECT",
+        "-R bw_data_saver 1 --jump REJECT",
     };
     expectIptablesCommands(expected);
 
     mBw.enableDataSaver(false);
     expected = {
-        "-R bw_costly_shared 3 --jump RETURN",
+        "-R bw_data_saver 1 --jump RETURN",
     };
     expectIptablesCommands(expected);
 }