Re: [PATCH RESEND 2/4] uaccess: Selectively open read or write user access

[Christophe Leroy <christophe.leroy@xxxxxx>]

Le 02/04/2020 à 09:51, Kees Cook a écrit :
> On Thu, Apr 02, 2020 at 07:34:17AM +0000, Christophe Leroy wrote:
> > [...]
> > diff --git a/kernel/compat.c b/kernel/compat.c
> > index 843dd17e6078..705ca7e418c6 100644
> > --- a/kernel/compat.c
> > +++ b/kernel/compat.c
> > @@ -199,7 +199,7 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
> >   	bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
> >   	nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
> >   
> > -	if (!user_access_begin(umask, bitmap_size / 8))
> > +	if (!user_write_access_begin(umask, bitmap_size / 8))
>
> This looks mismatched: should be user_read_access_begin()?

Oops, looks like a copy/paste/modify where I modified the original 
instead of the copy.


> >   		return -EFAULT;
> >   
> >   	while (nr_compat_longs > 1) {
> > @@ -211,11 +211,11 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
> >   	}
> >   	if (nr_compat_longs)
> >   		unsafe_get_user(*mask, umask++, Efault);
> > -	user_access_end();
> > +	user_read_access_end();
> >   	return 0;
> >   
> >   Efault:
> > -	user_access_end();
> > +	user_read_access_end();
> >   	return -EFAULT;
> >   }
>
> (These correctly end read access.)
>
> >   
> > @@ -228,7 +228,7 @@ long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
> >   	bitmap_size = ALIGN(bitmap_size, BITS_PER_COMPAT_LONG);
> >   	nr_compat_longs = BITS_TO_COMPAT_LONGS(bitmap_size);
> >   
> > -	if (!user_access_begin(umask, bitmap_size / 8))
> > +	if (!user_read_access_begin(umask, bitmap_size / 8))
>
> And ..._write_... here?
>
> >   		return -EFAULT;
> >   
> >   	while (nr_compat_longs > 1) {
> > @@ -239,10 +239,10 @@ long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
> >   	}
> >   	if (nr_compat_longs)
> >   		unsafe_put_user((compat_ulong_t)*mask, umask++, Efault);
> > -	user_access_end();
> > +	user_write_access_end();
> >   	return 0;
> >   Efault:
> > -	user_access_end();
> > +	user_write_access_end();
> >   	return -EFAULT;
> >   }
>
> (These correctly end write access.)
>
>
> All the others look correct. With the above fixed:
>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks
Christophe