telnet: fix false positive "Error writing to foreign host"

function                                             old     new   delta
write_to_net                                         620     625      +5

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 34 insertions, 28 deletions

diff --git a/networking/telnet.c b/networking/telnet.c
index 66fc0bdf1..a0eadc91b 100644
--- a/networking/telnet.c
+++ b/networking/telnet.c
@@ -164,8 +164,8 @@ struct globals {
 #define INITIAL_SENT    (1 << 2)
 #define DO_TERMIOS      (1 << 3)
 
-        byte            word_aligned_bytes[2];
-#define changed         word_aligned_bytes[0]
+        byte                word_aligned_bytes[2];
+#define changes_seen        word_aligned_bytes[0]
 #define CHANGED_ECHO        (1 << 0)
 #define CHANGED_NAWS        (1 << 1)
 // These happen only once:
@@ -173,14 +173,17 @@ struct globals {
 #define CHANGED_TTYPE       (1 << 3)
 #define CHANGED_NEW_ENVIRON (1 << 4)
 // The second byte is changed async, by signal handler:
-#define got_SIGWINCH    word_aligned_bytes[1]
-#define G_changed_word  (*(uint16_t*)G.word_aligned_bytes)
+#define got_SIGWINCH        word_aligned_bytes[1]
+#define G_changes_or_WINCH  (*(uint16_t*)G.word_aligned_bytes)
+// The "shared word" trick is unsafe on only-word-store arches such as DEC Alpha or SHARC,
+// but Alpha retired in 2004 and SHARC does not run linux (it's a DSP).
 
         byte            optstate_ECHO;
-#define OPT_ECHO_ON      1
-// We operate tty in rawmode only when echo ON (IOW: we saw server say that)
+// On program start:
+#define OPT_ECHO_UNKNOWN 0xff
 #define OPT_ECHO_OFF     0
-#define OPT_ECHO_UNKNOWN 0xff /* on program start */
+// We operate tty in rawmode only when echo ON (IOW: we saw server say that)
+#define OPT_ECHO_ON      1
 
         byte            echo_sga_response_size;
 
@@ -405,7 +408,7 @@ static void handle_changes_in_options(stdin_to_net_t *conn)
 {
         int count;
 
-        log1("changed:%x flags:%x", G.changed, G.flags);
+        log1("changed:%x flags:%x", G.changes_seen, G.flags);
 
         count = remaining_free_bytes(conn->size);
         // As soon as we see any DO/DONT/WILL/WONT known to us,
@@ -417,26 +420,26 @@ static void handle_changes_in_options(stdin_to_net_t *conn)
         // only if that option was requested.
         // We repeatedly send only NAWS (when our window changes).
         // Repeated DO requests are ignored.
-        if (G.changed
+        if (G.changes_seen
          && (count >= G.echo_sga_response_size)
         ) {
-                if (G.changed & CHANGED_ECHO) {
+                if (G.changes_seen & CHANGED_ECHO) {
                         // Server said WILL/WONT ECHO - confirm every time
                         log1("C:%s ECHO", G.optstate_ECHO ? "DO" : "DONT");
                         put_iac3_IAC_x_y(G.optstate_ECHO ? DO : DONT, TELOPT_ECHO);
                 }
-                if (G.changed & CHANGED_SGA) {
+                if (G.changes_seen & CHANGED_SGA) {
                         // Server said WILL SGA - confirm once
                         log1("C:DO SGA");
                         put_iac3_IAC_x_y(DO, TELOPT_SGA);
                         G.flags |= FLAGS_SGA_SEEN; // remember we did it
-                        G.changed -= CHANGED_SGA;
+                        G.changes_seen -= CHANGED_SGA;
                 }
-                G.changed &= ~(CHANGED_ECHO|CHANGED_SGA);
+                G.changes_seen &= ~(CHANGED_ECHO|CHANGED_SGA);
 
                 if (!(G.flags & INITIAL_SENT)) {
                         // From now on, we'll only do DO/DONT ECHO and maybe DO SGA
-                        // in the "if (G.changed)" block.
+                        // in the "if (G.changes_seen)" block.
                         G.flags |= INITIAL_SENT;
                         G.echo_sga_response_size = (G.flags & FLAGS_SGA_SEEN) ? 3 : 6;
 
@@ -466,9 +469,9 @@ static void handle_changes_in_options(stdin_to_net_t *conn)
         // Therefore we always send WILL X before SB X...
 #if ENABLE_FEATURE_TELNET_WIDTH
         if (remaining_free_bytes(conn->size) > MAX_NAWS_SIZE) {
-                if (G.changed & CHANGED_NAWS) {
+                if (G.changes_seen & CHANGED_NAWS) {
                         G.flags |= FLAGS_NAWS_ON; // remember we did it
-                        G.changed -= CHANGED_NAWS;
+                        G.changes_seen -= CHANGED_NAWS;
                         goto generate_naws;
                 }
                 // Handle window resize: send updated NAWS
@@ -484,23 +487,23 @@ static void handle_changes_in_options(stdin_to_net_t *conn)
         }
 #endif
 #if ENABLE_FEATURE_TELNET_TTYPE
-        if ((G.changed & CHANGED_TTYPE)
+        if ((G.changes_seen & CHANGED_TTYPE)
          && remaining_free_bytes(conn->size) > 6 + 2 * strlen(G.ttype)
         ) {
                 log1("C:SB %s '%s'", "TTYPE", G.ttype);
                 put_iac_subopt(TELOPT_TTYPE, G.ttype);
                 G.ttype = NULL; // remember we did it
-                G.changed -= CHANGED_TTYPE;
+                G.changes_seen -= CHANGED_TTYPE;
         }
 #endif
 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
-        if ((G.changed & CHANGED_NEW_ENVIRON)
+        if ((G.changes_seen & CHANGED_NEW_ENVIRON)
          && remaining_free_bytes(conn->size) > 12 + 2 * strlen(G.autologin)
         ) {
                 log1("C:SB %s '%s'", "NEW_ENVIRON", G.autologin);
                 put_iac_subopt_autologin(G.autologin);
                 G.autologin = NULL; // remember we did it
-                G.changed -= CHANGED_NEW_ENVIRON;
+                G.changes_seen -= CHANGED_NEW_ENVIRON;
         }
 #endif
 }
@@ -556,7 +559,7 @@ static void show_menu(void)
                         announce_rawmode(); /* no "_and_switch_": we are already in rawmode */
  echo_changed:
                         if (G.flags & INITIAL_SENT)
-                                G.changed |= CHANGED_ECHO; /* inform the server at next send */
+                                G.changes_seen |= CHANGED_ECHO; /* inform the server at next send */
                         return;
                 }
                 break;
@@ -663,7 +666,7 @@ static int have_data_to_write_to_net(void *this)
                 ioloop_remove_conn(conn->io, (connection_t*)conn);
                 return -1;
         }
-        return conn->size > 0 || G_changed_word != 0;
+        return conn->size > 0 || G_changes_or_WINCH != 0;
 }
 
 static int write_to_net(void *this)
@@ -672,10 +675,13 @@ static int write_to_net(void *this)
         int count;
 
         /* Do we have option or NAWS changes to handle? */
-        if (G_changed_word)
+        if (G_changes_or_WINCH)
                 handle_changes_in_options(conn); /* yes */
 
         count = MIN(BUFSIZE - conn->wridx, conn->size);
+        // can be zero due to handle_changes_in_options()
+        if (count == 0)
+                return 0;
         count = safe_write(conn->write_fd, BUF_TTY2NET + conn->wridx, count);
         if (count <= 0) {
                 if (count < 0 && errno == EAGAIN)
@@ -814,7 +820,7 @@ static int read_from_net(void *this)
                                         break;
                                 case TELOPT_SGA: /* Remote option: "suppress go ahead" */
                                         if (will && !(G.flags & FLAGS_SGA_SEEN))
-                                                G.changed |= CHANGED_SGA;
+                                                G.changes_seen |= CHANGED_SGA;
                                         break;
                                 }
                         } else if (conn->negotiation_verb == DO) {
@@ -823,19 +829,19 @@ static int read_from_net(void *this)
                                 case TELOPT_TTYPE: /* Local option: we send terminal type */
                                         log1("TTYPE:'%s' %ssetting CHANGED_TTYPE", G.ttype, G.ttype ? "" : "not ");
                                         if (G.ttype)
-                                                G.changed |= CHANGED_TTYPE;
+                                                G.changes_seen |= CHANGED_TTYPE;
                                         break;
 #endif
 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
                                 case TELOPT_NEW_ENVIRON: /* Local option: we send username */
                                         if (G.autologin)
-                                                G.changed |= CHANGED_NEW_ENVIRON;
+                                                G.changes_seen |= CHANGED_NEW_ENVIRON;
                                         break;
 #endif
 #if ENABLE_FEATURE_TELNET_WIDTH
                                 case TELOPT_NAWS: /* Local option: we send window size */
                                         if (!(G.flags & FLAGS_NAWS_ON))
-                                                G.changed |= CHANGED_NAWS;
+                                                G.changes_seen |= CHANGED_NAWS;
                                         break;
 #endif
                                 }
@@ -873,7 +879,7 @@ static int read_from_net(void *this)
 
         if (oldstate_ECHO != G.optstate_ECHO) {
                 /* Tell net writer to generate a confirmation */
-                G.changed |= CHANGED_ECHO;
+                G.changes_seen |= CHANGED_ECHO;
                 /* Print the banner and set termios */
                 if (G.optstate_ECHO == OPT_ECHO_ON)
                         announce_and_switch_to_rawmode();