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

From: Kees Cook <[email-masked]>
Date: Thu, 2 Apr 2020 00:51:26 -0700

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()?

>  		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 <[email-masked]>

-- 
Kees Cook