From 8d84272d80e07ae8255f14acb025c2aeee323557 Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Sat, 30 Mar 2019 07:28:38 +0000
Subject: [PATCH] uxserver: option to generate numeric "exit-signal".

This mimics a bug in some old SSH servers for which PuTTY contains
compensation code (parsing an incoming "exit-signal" two ways and
seeing which one worked). I completely rewrote that code in commit
7535f645a, as part of the BinarySource rework. Now I can finally test
it sensibly.
---
 sesschan.c      | 34 ++++++++++++++++++++++++----------
 sshserver.h     |  3 +++
 unix/uxpty.c    | 18 ++++++++++++------
 unix/uxserver.c |  2 ++
 4 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/sesschan.c b/sesschan.c
index 5a7ffcfc..39e7f7fd 100644
--- a/sesschan.c
+++ b/sesschan.c
@@ -608,25 +608,39 @@ static bool sesschan_seat_eof(Seat *seat)
 static void sesschan_notify_remote_exit(Seat *seat)
 {
     sesschan *sess = container_of(seat, sesschan, seat);
-    ptrlen signame;
-    char *sigmsg;
 
     if (!sess->backend)
         return;
 
-    signame = pty_backend_exit_signame(sess->backend, &sigmsg);
-    if (signame.len) {
-        if (!sigmsg)
-            sigmsg = dupstr("");
+    bool got_signal = false;
+    if (!sess->ssc->exit_signal_numeric) {
+        char *sigmsg;
+        ptrlen signame = pty_backend_exit_signame(sess->backend, &sigmsg);
 
-        sshfwd_send_exit_signal(
-            sess->c, signame, false, ptrlen_from_asciz(sigmsg));
+        if (signame.len) {
+            if (!sigmsg)
+                sigmsg = dupstr("");
 
-        sfree(sigmsg);
+            sshfwd_send_exit_signal(
+                sess->c, signame, false, ptrlen_from_asciz(sigmsg));
+
+            sfree(sigmsg);
+
+            got_signal = true;
+        }
     } else {
-        sshfwd_send_exit_status(sess->c, backend_exitcode(sess->backend));
+        int signum = pty_backend_exit_signum(sess->backend);
+
+        if (signum >= 0) {
+            sshfwd_send_exit_signal_numeric(sess->c, signum, false,
+                                            PTRLEN_LITERAL(""));
+            got_signal = true;
+        }
     }
 
+    if (!got_signal)
+        sshfwd_send_exit_status(sess->c, backend_exitcode(sess->backend));
+
     sess->seen_exit = true;
     queue_toplevel_callback(sesschan_check_close_callback, sess);
 }
diff --git a/sshserver.h b/sshserver.h
index 4df5c230..2ed06b9d 100644
--- a/sshserver.h
+++ b/sshserver.h
@@ -2,6 +2,8 @@ typedef struct AuthPolicy AuthPolicy;
 
 struct SshServerConfig {
     ptrlen banner;        /* banner.ptr == NULL indicates no banner */
+
+    bool exit_signal_numeric;          /* mimic an old server bug */
 };
 
 Plug *ssh_server_plug(
@@ -94,6 +96,7 @@ Channel *sesschan_new(SshChannel *c, LogContext *logctx,
 Backend *pty_backend_create(
     Seat *seat, LogContext *logctx, Conf *conf, char **argv, const char *cmd,
     struct ssh_ttymodes ttymodes, bool pipes_instead_of_pty);
+int pty_backend_exit_signum(Backend *be);
 ptrlen pty_backend_exit_signame(Backend *be, char **aux_msg);
 
 /*
diff --git a/unix/uxpty.c b/unix/uxpty.c
index 93721358..0c7e820c 100644
--- a/unix/uxpty.c
+++ b/unix/uxpty.c
@@ -1526,17 +1526,23 @@ static int pty_exitcode(Backend *be)
         return WEXITSTATUS(pty->exit_code);
 }
 
-ptrlen pty_backend_exit_signame(Backend *be, char **aux_msg)
+int pty_backend_exit_signum(Backend *be)
 {
     Pty *pty = container_of(be, Pty, backend);
-    int sig;
-
-    *aux_msg = NULL;
 
     if (!pty->finished || !WIFSIGNALED(pty->exit_code))
-	return PTRLEN_LITERAL("");
+	return -1;
 
-    sig = WTERMSIG(pty->exit_code);
+    return WTERMSIG(pty->exit_code);
+}
+
+ptrlen pty_backend_exit_signame(Backend *be, char **aux_msg)
+{
+    *aux_msg = NULL;
+
+    int sig = pty_backend_exit_signum(be);
+    if (sig < 0)
+	return PTRLEN_LITERAL("");
 
 #define TRANSLATE_SIGNAL(s) do                          \
     {                                                   \
diff --git a/unix/uxserver.c b/unix/uxserver.c
index f9da9bed..b14f93db 100644
--- a/unix/uxserver.c
+++ b/unix/uxserver.c
@@ -542,6 +542,8 @@ int main(int argc, char **argv)
             ssc.banner = ptrlen_from_strbuf(sb);
         } else if (longoptarg(arg, "--bannertext", &val, &argc, &argv)) {
             ssc.banner = ptrlen_from_asciz(val);
+        } else if (longoptnoarg(arg, "--exitsignum")) {
+            ssc.exit_signal_numeric = true;
         } else if (longoptarg(arg, "--sshlog", &val, &argc, &argv) ||
                    longoptarg(arg, "-sshlog", &val, &argc, &argv)) {
             Filename *logfile = filename_from_str(val);