Merge branch 'lukas/kernel/os_cmd_fix_exit_message_leak/OTP-13813' into maint-19

* lukas/kernel/os_cmd_fix_exit_message_leak/OTP-13813:
  erts: Make sure to flush potential exit message

2 files changed, 30 insertions, 8 deletions

diff --git a/lib/kernel/src/os.erl b/lib/kernel/src/os.erl
index 81b70a7fee..05bbf1069e 100644
--- a/lib/kernel/src/os.erl
+++ b/lib/kernel/src/os.erl
@@ -279,15 +279,11 @@ get_data(Port, MonRef, Eot, Sofar) ->
                 Last ->
                     Port ! {self(), close},
                     flush_until_closed(Port),
+                    flush_exit(Port),
                     iolist_to_binary([Sofar, Last])
             end;
         {'DOWN', MonRef, _, _ , _} ->
-	    receive
-		{'EXIT',  Port,  _} ->
-		    ok
-	    after 1 ->				% force context switch
-		    ok
-	    end,
+	    flush_exit(Port),
 	    iolist_to_binary(Sofar)
     end.
 
@@ -307,3 +303,11 @@ flush_until_closed(Port) ->
         {Port, closed} ->
             true
     end.
+
+flush_exit(Port) ->
+    receive
+        {'EXIT',  Port,  _} ->
+            ok
+    after 1 ->				% force context switch
+            ok
+    end.
diff --git a/lib/kernel/test/os_SUITE.erl b/lib/kernel/test/os_SUITE.erl
index 8f3e511941..19ab3713a1 100644
--- a/lib/kernel/test/os_SUITE.erl
+++ b/lib/kernel/test/os_SUITE.erl
@@ -25,7 +25,7 @@
 -export([space_in_cwd/1, quoting/1, cmd_unicode/1, space_in_name/1, bad_command/1,
 	 find_executable/1, unix_comment_in_command/1, deep_list_command/1,
          large_output_command/1, background_command/0, background_command/1,
-         perf_counter_api/1]).
+         message_leak/1, perf_counter_api/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -36,7 +36,8 @@ suite() ->
 all() ->
     [space_in_cwd, quoting, cmd_unicode, space_in_name, bad_command,
      find_executable, unix_comment_in_command, deep_list_command,
-     large_output_command, background_command, perf_counter_api].
+     large_output_command, background_command, message_leak,
+     perf_counter_api].
 
 groups() ->
     [].
@@ -284,6 +285,23 @@ background_command(_Config) ->
     %% longer then the 5 second timeout
     os:cmd("sleep 10&").
 
+%% Test that message does not leak to the calling process
+message_leak(_Config) ->
+    process_flag(trap_exit, true),
+
+    os:cmd("echo hello"),
+    [] = receive_all(),
+
+    case os:type() of
+        {unix, _} ->
+            os:cmd("while true; do echo hello; done&"),
+            [] = receive_all();
+        _ ->
+            ok % Cannot background on non-unix
+    end,
+
+    process_flag(trap_exit, false).
+
 %% Test that the os:perf_counter api works as expected
 perf_counter_api(_Config) ->