From: Hanno Böck <hanno@xxxxxxxxx> TIOCLINUX can be used for privilege escalation on virtual terminals when code is executed via tools like su/sudo and sandboxing tools. By abusing the selection features, a lower-privileged application can write content to the console, select and copy/paste that content and thereby executing code on the privileged account. See also the poc here: https://www.openwall.com/lists/oss-security/2023/03/14/3 Selection is usually used by tools like gpm that provide mouse features on the virtual console. gpm already runs as root (due to earlier changes that restrict access to a user on the current TTY), therefore it will still work with this change. With this change, the following TIOCLINUX subcommands require CAP_SYS_ADMIN: * TIOCL_SETSEL - setting the selected region on the terminal * TIOCL_PASTESEL - pasting the contents of the selected region into the input buffer * TIOCL_SELLOADLUT - changing word-by-word selection behaviour The security problem mitigated is similar to the security risks caused by TIOCSTI, which, since kernel 6.2, can be disabled with CONFIG_LEGACY_TIOCSTI=n. Signed-off-by: Hanno Böck <hanno@xxxxxxxxx> Tested-by: Günther Noack <gnoack@xxxxxxxxxx> --- drivers/tty/vt/vt.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 1e8e57b45688..1eb30ed1118d 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -3156,9 +3156,13 @@ int tioclinux(struct tty_struct *tty, unsigned long arg) switch (type) { case TIOCL_SETSEL: + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; return set_selection_user((struct tiocl_selection __user *)(p+1), tty); case TIOCL_PASTESEL: + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; return paste_selection(tty); case TIOCL_UNBLANKSCREEN: console_lock(); @@ -3166,6 +3170,8 @@ int tioclinux(struct tty_struct *tty, unsigned long arg) console_unlock(); break; case TIOCL_SELLOADLUT: + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; console_lock(); ret = sel_loadlut(p); console_unlock(); -- 2.42.0.rc2.253.gd59a3bf2b4-goog
