Re: [PATCH 16/36] tty/vt: consolemap: check put_user() in con_get_unimap()

[Jiri Slaby]

On 08. 06. 22, 10:02, David Laight wrote:
> From: Jiri Slaby
> > Sent: 07 June 2022 11:49
> >
> > Only the return value of copy_to_user() is checked in con_get_unimap().
> > Do the same for put_user() of the count too.
> >
> > Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
> > ---
> >   drivers/tty/vt/consolemap.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
> > index 831450f2bfd1..92b5dddb00d9 100644
> > --- a/drivers/tty/vt/consolemap.c
> > +++ b/drivers/tty/vt/consolemap.c
> > @@ -813,7 +813,8 @@ int con_get_unimap(struct vc_data *vc, ushort ct, ushort __user *uct,
> >   	console_unlock();
> >   	if (copy_to_user(list, unilist, min(ect, ct) * sizeof(*unilist)))
> >   		ret = -EFAULT;
> > -	put_user(ect, uct);
> > +	if (put_user(ect, uct))
> > +		ret = -EFAULT;
> >   	kvfree(unilist);
> >   	return ret ? ret : (ect <= ct) ? 0 : -ENOMEM;
> >   }
>
> How is the user expected to check the result of this code?
>
> AFAICT -ENOMEM is returned if either kmalloc() fails or
> the user buffer is too short?
> Looks pretty hard to detect which.

Agreed. The code is far from perfect. We might try to return ENOSPC and 
watch what breaks. (And decouple the double "?:" operator as it makes 
things only worse.)

> I've not looked at the effect of all the patches, but setting
> 'ret = -ENOMEM' and breaking the loop when the array is too
> small would simplify things.

Note that the patches try NOT to change the behavior in any way. If they 
do, it's likely a bug. They are first front cleanup. Definitely more to 
come. Either from me, or others -- patches welcome ;).

thanks,
--
js
suse labs