On Fri, Dec 15, 2023 at 04:28:53PM +0800, Zijun Hu wrote:
> Function tty_ldisc_get() has a simple logical error and may cause tty-ldisc
> module to be loaded by a user without CAP_SYS_MODULE, this security issue
> is fixed by correcting the logical error.
What specific security issue are you referring to here?
> Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
> ---
> drivers/tty/tty_ldisc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
> index 3f68e213df1f..b490c0adf00f 100644
> --- a/drivers/tty/tty_ldisc.c
> +++ b/drivers/tty/tty_ldisc.c
> @@ -150,7 +150,7 @@ static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
> */
> ldops = get_ldops(disc);
> if (IS_ERR(ldops)) {
> - if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
> + if (!capable(CAP_SYS_MODULE) || !tty_ldisc_autoload)
I'm missing something, why change this?
Remember if tty_ldisc_autoload is enabled, then any user can auto-load a
tty ldisc, permissions are not needed.
as it's confusing to read, let me break this down to see if the original
code is correct or not:
If you do NOT have CAP_SYS_MODULE AND you do NOT have
tty_ldisc_autoload enabled, then the kernel will NOT call
request_module
If you do have CAP_SYS_MODULE enabled then the kernel will call
request_module()
If you do have tty_ldisc_autoload enabled, then you can autoload
a module.
Is this not the correct functionality?
You are changing this to:
If you do NOT have CAP_SYS_MODULE enabled, then no matter what,
do NOT call request_module()
If you do NOT have tty_ldisc_autoload enabled, then no matter
what, do NOT call request_module()
Are you sure that's what you want to change this to?
What am I missing here?
confused,
greg "boolean logic is hard" k-h
