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c920ecd73

Denys Vlasenko
Denys Vlasenko
2026-02-24
SUCCESS Duration: 145s

Subject

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

Binary

No binary (build failed)

Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0 
gcc -Wp,-MD,applets/.usage.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer      -Iinclude -Iinclude -o applets/usage applets/usage.c

Build Log

(log yok)

Commit Diff GitHub →

networking/telnet.c +34 -28
networking/telnet.c+34 -28
@@ -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();