Re: [PATCH] tty: vt: add a bounds checking in vt_do_kdgkb_ioctl()

From: Jiri Slaby
Date: Thu Sep 08 2022 - 04:10:45 EST

On 08. 09. 22, 9:54, Hangyu Hua wrote:
As array_index_nospec's comments indicate,a bounds checking need to add
before calling array_index_nospec.

Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
drivers/tty/vt/keyboard.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index be8313cdbac3..b9845455df79 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -2067,6 +2067,9 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
if (get_user(kb_func, &user_kdgkb->kb_func))
return -EFAULT;
+ if (kb_func >= MAX_NR_FUNC)

kb_func is unsigned char and MAX_NR_FUNC is 256. So this should be eliminated by the compiler anyway.

But the check might be a good idea if we ever decide to support more keys. But will/can we? I am not so sure, so adding it right now is kind of superfluous. In any way we'd need to introduce a completely different iterface/ioctls.

+ return -EFAULT;

EINVAL would be more appropriate, IMO.

kb_func = array_index_nospec(kb_func, MAX_NR_FUNC);
switch (cmd) {

suse labs