[PATCH 1/2] vt_ioctl: fix array_index_nospec in vt_setactivate

[PATCH 1/2] vt_ioctl: fix array_index_nospec in vt_setactivate

[Jakob Koschel]

array_index_nospec ensures that an out-of-bounds value is set to zero
on the transient path. Decreasing the value by one afterwards causes
a transient integer underflow. vsa.console should be decreased first
and then sanitized with array_index_nospec.

Kasper Acknowledgements: Jakob Koschel, Brian Johannesmeyer, Kaveh
Razavi, Herbert Bos, Cristiano Giuffrida from the VUSec group at VU
Amsterdam.

Co-developed-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
---
 drivers/tty/vt/vt_ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
index 3639bb6dc372..e0714a9c9fd7 100644
--- a/drivers/tty/vt/vt_ioctl.c
+++ b/drivers/tty/vt/vt_ioctl.c
@@ -599,8 +599,8 @@ static int vt_setactivate(struct vt_setactivate __user *sa)
 	if (vsa.console == 0 || vsa.console > MAX_NR_CONSOLES)
 		return -ENXIO;

-	vsa.console = array_index_nospec(vsa.console, MAX_NR_CONSOLES + 1);
 	vsa.console--;
+	vsa.console = array_index_nospec(vsa.console, MAX_NR_CONSOLES);
 	console_lock();
 	ret = vc_allocate(vsa.console);
 	if (ret) {
--
2.25.1

[PATCH 2/2] vt_ioctl: add array_index_nospec to VT_ACTIVATE

[Jakob Koschel]

in vt_setactivate an almost identical code path has been patched
with array_index_nospec. In the VT_ACTIVATE path the user input
is from a system call argument instead of a usercopy.
For consistency both code paths should have the same mitigations
applied.

Kasper Acknowledgements: Jakob Koschel, Brian Johannesmeyer, Kaveh
Razavi, Herbert Bos, Cristiano Giuffrida from the VUSec group at VU
Amsterdam.

Co-developed-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
---
 drivers/tty/vt/vt_ioctl.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
index e0714a9c9fd7..58013698635f 100644
--- a/drivers/tty/vt/vt_ioctl.c
+++ b/drivers/tty/vt/vt_ioctl.c
@@ -845,6 +845,7 @@ int vt_ioctl(struct tty_struct *tty,
 			return -ENXIO;

 		arg--;
+		arg = array_index_nospec(arg, MAX_NR_CONSOLES);
 		console_lock();
 		ret = vc_allocate(arg);
 		console_unlock();
--
2.25.1