CONFIG_LEGACY_TIOCSTI

README.md

@@ -92,6 +92,44 @@ Can I send some text to the STDIN of an active process running in a screen sessi
 * https://serverfault.com/questions/178457/can-i-send-some-text-to-the-stdin-of-an-active-process-running-in-a-screen-sessi
 
 
+# Linux Kernel Note
+I see this configuration option and note in a 6.5 kernel:
+
+```
+CONFIG_LEGACY_TIOCSTI:
+Historically the kernel has allowed TIOCSTI, which will push
+characters into a controlling TTY. This continues to be used
+as a malicious privilege escalation mechanism, and provides no
+meaningful real-world utility any more. Its use is considered
+a dangerous legacy operation, and can be disabled on most
+systems.
+
+Say Y here only if you have confirmed that your system's
+userspace depends on this functionality to continue operating
+normally.
+
+Processes which run with CAP_SYS_ADMIN, such as BRLTTY, can
+use TIOCSTI even when this is set to N.
+
+This functionality can be changed at runtime with the
+dev.tty.legacy_tiocsti sysctl. This configuration option sets
+the default value of the sysctl.
+
+Symbol: LEGACY_TIOCSTI [=y]
+Type  : bool
+Defined at drivers/tty/Kconfig:152
+Prompt: Allow legacy TIOCSTI usage
+Depends on: TTY [=y]
+  Location:
+    -> Device Drivers
+      -> Character devices
+        -> Enable TTY (TTY [=y])
+          -> Allow legacy TIOCSTI usage (LEGACY_TIOCSTI [=y])
+```
+
+:)
+
+
 # License
 MIT.