[PATCH AUTOSEL 5.15 10/50] tty: fix out-of-bounds access in tty_driver_lookup_tty()

Sasha Levin
2023-03-03T21:51:58Z

From: Sven Schnelle <svens@linux.ibm.com>

[ Upstream commit db4df8e9d79e7d37732c1a1b560958e8dadfefa1 ]

When specifying an invalid console= device like console=tty3270,
tty_driver_lookup_tty() returns the tty struct without checking
whether index is a valid number.

To reproduce:

qemu-system-x86_64 -enable-kvm -nographic -serial mon:stdio \
-kernel ../linux-build-x86/arch/x86/boot/bzImage \
-append "console=ttyS0 console=tty3270"

This crashes with:

[ 0.770599] BUG: kernel NULL pointer dereference, address: 00000000000000ef
[ 0.771265] #PF: supervisor read access in kernel mode
[ 0.771773] #PF: error_code(0x0000) - not-present page
[ 0.772609] Oops: 0000 [#1] PREEMPT SMP PTI
[ 0.774878] RIP: 0010:tty_open+0x268/0x6f0
[ 0.784013] chrdev_open+0xbd/0x230
[ 0.784444] ? cdev_device_add+0x80/0x80
[ 0.784920] do_dentry_open+0x1e0/0x410
[ 0.785389] path_openat+0xca9/0x1050
[ 0.785813] do_filp_open+0xaa/0x150
[ 0.786240] file_open_name+0x133/0x1b0
[ 0.786746] filp_open+0x27/0x50
[ 0.787244] console_on_rootfs+0x14/0x4d
[ 0.787800] kernel_init_freeable+0x1e4/0x20d
[ 0.788383] ? rest_init+0xc0/0xc0
[ 0.788881] kernel_init+0x11/0x120
[ 0.789356] ret_from_fork+0x22/0x30

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221209112737.3222509-2-svens@linux.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/tty_io.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 6616d4a0d41de..64dd6439d1797 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1244,14 +1244,16 @@ static struct tty_struct *tty_driver_lookup_tty(struct tty_driver *driver,
{
struct tty_struct *tty;

- if (driver->ops->lookup)
+ if (driver->ops->lookup) {
if (!file)
tty = ERR_PTR(-EIO);
else
tty = driver->ops->lookup(driver, file, idx);
- else
+ } else {
+ if (idx >= driver->num)
+ return ERR_PTR(-EINVAL);
tty = driver->ttys[idx];
-
+ }
if (!IS_ERR(tty))
tty_kref_get(tty);
return tty;
--
2.39.2