[PATCH V33 19/30] Lock down TIOCSSERIAL
From: Matthew Garrett <hidden>
Date: 2019-06-21 01:20:48
Also in:
linux-serial, lkml
Subsystem:
lockdown security module, security subsystem, the rest, tty layer and serial drivers · Maintainers:
Nicolas Bouchinet, Xiu Jianfeng, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds, Greg Kroah-Hartman, Jiri Slaby
From: David Howells <dhowells@redhat.com> Lock down TIOCSSERIAL as that can be used to change the ioport and irq settings on a serial port. This only appears to be an issue for the serial drivers that use the core serial code. All other drivers seem to either ignore attempts to change port/irq or give an error. Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Matthew Garrett <redacted> cc: Jiri Slaby <redacted> Cc: linux-serial@vger.kernel.org --- drivers/tty/serial/serial_core.c | 7 +++++++ include/linux/security.h | 1 + security/lockdown/lockdown.c | 1 + 3 files changed, 9 insertions(+)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 351843f847c0..2dbef7dc23f6 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c@@ -22,6 +22,7 @@ #include <linux/serial_core.h> #include <linux/delay.h> #include <linux/mutex.h> +#include <linux/security.h> #include <linux/irq.h> #include <linux/uaccess.h>
@@ -852,6 +853,12 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port, new_flags = (__force upf_t)new_info->flags; old_custom_divisor = uport->custom_divisor; + if ((change_port || change_irq) && + security_is_locked_down(LOCKDOWN_TIOCSSERIAL)) { + retval = -EPERM; + goto exit; + } + if (!capable(CAP_SYS_ADMIN)) { retval = -EPERM; if (change_irq || change_port ||
diff --git a/include/linux/security.h b/include/linux/security.h
index 87c433f1e7db..cb5d74f9b9ff 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h@@ -91,6 +91,7 @@ enum lockdown_reason { LOCKDOWN_MSR, LOCKDOWN_ACPI_TABLES, LOCKDOWN_PCMCIA_CIS, + LOCKDOWN_TIOCSSERIAL, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_CONFIDENTIALITY_MAX, };
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index ced4ddbb36b4..c6456f300220 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c@@ -27,6 +27,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_MSR] = "raw MSR access", [LOCKDOWN_ACPI_TABLES] = "modified ACPI tables", [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage", + [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO", [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", };
--
2.22.0.410.gd8fdbe21b5-goog