From: Karel Zak <kzak@redhat.com>
Date: Tue, 28 Jul 2026 12:16:31 +0000 (+0200)
Subject: pty-session: defer raw mode until after signals are blocked
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=288b503e6f2f02fcfda10ff718e85b2367460cf0;p=thirdparty%2Futil-linux.git

pty-session: defer raw mode until after signals are blocked

ul_pty_setup() switches the user's terminal to raw mode before
ul_pty_signals_setup() blocks signals. A terminating signal delivered
in this window kills the process without reaching ul_pty_cleanup(),
leaving the terminal in raw mode.

Move the raw-mode tcsetattr() out of ul_pty_setup() into a new
ul_pty_terminal_setup() function, to be called after
ul_pty_signals_setup(). This ensures signals are already directed
to signalfd when raw mode is activated, closing the race window.

The setup sequence is now:
  ul_pty_setup()          -- open pty, save terminal attrs
  <app-specific work>     -- e.g. utempter (needs SIGCHLD unblocked)
  ul_pty_signals_setup()  -- block signals, create signalfd
  ul_pty_terminal_setup() -- set raw mode (signals already blocked)
  fork()

Addresses: https://github.com/util-linux/util-linux/issues/4499
Signed-off-by: Karel Zak <kzak@redhat.com>
---

diff --git a/include/pty-session.h b/include/pty-session.h
index af54197b3..a91db2af6 100644
--- a/include/pty-session.h
+++ b/include/pty-session.h
@@ -108,6 +108,7 @@ struct ul_pty_callbacks *ul_pty_get_callbacks(struct ul_pty *pty);
 int ul_pty_is_running(struct ul_pty *pty);
 int ul_pty_setup(struct ul_pty *pty);
 int ul_pty_signals_setup(struct ul_pty *pty);
+int ul_pty_terminal_setup(struct ul_pty *pty);
 void ul_pty_cleanup(struct ul_pty *pty);
 int ul_pty_chownmod_slave(struct ul_pty *pty, uid_t uid, gid_t gid, mode_t mode);
 void ul_pty_init_slave(struct ul_pty *pty);
diff --git a/lib/pty-session.c b/lib/pty-session.c
index 12d7326a2..d72ea6c42 100644
--- a/lib/pty-session.c
+++ b/lib/pty-session.c
@@ -186,9 +186,6 @@ int ul_pty_setup(struct ul_pty *pty)
 		if (rc)
 			goto done;
 
-		/* set the current terminal to raw mode; pty_cleanup() reverses this change on exit */
-		cfmakeraw(&attrs);
-		tcsetattr(STDIN_FILENO, TCSANOW, &attrs);
 	} else {
 		DBG_OBJ(SETUP, pty, ul_debug("create for non-terminal"));
 
@@ -217,6 +214,23 @@ done:
 	return rc;
 }
 
+/* call me after ul_pty_signals_setup() and before fork() */
+int ul_pty_terminal_setup(struct ul_pty *pty)
+{
+	struct termios attrs;
+
+	if (!pty->isterm)
+		return 0;
+
+	attrs = pty->stdin_attrs;
+	cfmakeraw(&attrs);
+	if (tcsetattr(STDIN_FILENO, TCSANOW, &attrs))
+		return -errno;
+
+	DBG_OBJ(SETUP, pty, ul_debug("terminal raw mode setup done"));
+	return 0;
+}
+
 /* call me before fork() */
 int ul_pty_signals_setup(struct ul_pty *pty)
 {
@@ -806,6 +820,8 @@ int main(int argc, char *argv[])
 		err(EXIT_FAILURE, "failed to create pseudo-terminal");
 	if (ul_pty_signals_setup(pty))
 		err(EXIT_FAILURE, "failed to initialize signals handler");
+	if (ul_pty_terminal_setup(pty))
+		err(EXIT_FAILURE, "failed to setup terminal");
 
 	fflush(stdout);			/* ??? */
 
diff --git a/login-utils/su-common.c b/login-utils/su-common.c
index c4b30f39a..2e349e82e 100644
--- a/login-utils/su-common.c
+++ b/login-utils/su-common.c
@@ -564,6 +564,10 @@ static void create_watching_parent(struct su_context *su)
 			supam_cleanup(su, PAM_ABORT);
 			err(EXIT_FAILURE, _("failed to initialize signals handler"));
 		}
+		if (ul_pty_terminal_setup(su->pty)) {
+			supam_cleanup(su, PAM_ABORT);
+			err(EXIT_FAILURE, _("failed to setup terminal"));
+		}
 	}
 #endif
 	fflush(stdout);			/* ??? */
diff --git a/term-utils/script.c b/term-utils/script.c
index 3991ea646..d84b61111 100644
--- a/term-utils/script.c
+++ b/term-utils/script.c
@@ -1027,6 +1027,8 @@ int main(int argc, char **argv)
 
 	if (ul_pty_signals_setup(ctl.pty))
 		err(EXIT_FAILURE, _("failed to initialize signals handler"));
+	if (ul_pty_terminal_setup(ctl.pty))
+		err(EXIT_FAILURE, _("failed to setup terminal"));
 	fflush(stdout);
 
 	/*
diff --git a/term-utils/scriptlive.c b/term-utils/scriptlive.c
index bf7c31244..95bcbb5c7 100644
--- a/term-utils/scriptlive.c
+++ b/term-utils/scriptlive.c
@@ -305,6 +305,8 @@ main(int argc, char *argv[])
 		err(EXIT_FAILURE, _("failed to create pseudo-terminal"));
 	if (ul_pty_signals_setup(ss.pty))
 		err(EXIT_FAILURE, _("failed to initialize signals handler"));
+	if (ul_pty_terminal_setup(ss.pty))
+		err(EXIT_FAILURE, _("failed to setup terminal"));
 
 	fflush(stdout);			/* ??? */