linux-kernel - Re: [PATCH] drivers/tty/vt: copy userspace arrays safely

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Date:   Thu, 2 Nov 2023 20:14:24 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Philipp Stanner <pstanner@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Tony Luck <tony.luck@...el.com>,
        Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org, Dave Airlie <airlied@...hat.com>
Subject: Re: [PATCH] drivers/tty/vt: copy userspace arrays safely

On Thu, Nov 02, 2023 at 08:21:35PM +0100, Philipp Stanner wrote:
> The functions (v)memdup_user() are utilized to copy userspace arrays.
> This is done without overflow checks.
> 
> Use the new wrappers memdup_array_user() and vmemdup_array_user() to
> copy the arrays more safely.

> @@ -644,7 +644,7 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
>  	if (!ct)
>  		return 0;

> -	unilist = vmemdup_user(list, array_size(sizeof(*unilist), ct));
> +	unilist = vmemdup_array_user(list, ct, sizeof(*unilist));
>  	if (IS_ERR(unilist))
>  		return PTR_ERR(unilist);

a 16bit value times sizeof(something).
  
> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
> index 1fe6107b539b..802ceb0a5e4c 100644
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -1773,8 +1773,8 @@ int vt_do_diacrit(unsigned int cmd, void __user *udp, int perm)

... and here we have
                if (ct >= MAX_DIACR)
			return -EINVAL;

directly upstream, so it's even better - a value below 256 times sizeof(something)

>  		if (ct) {
>  
> -			dia = memdup_user(a->kbdiacr,
> -					sizeof(struct kbdiacr) * ct);
> +			dia = memdup_array_user(a->kbdiacr,
> +						ct, sizeof(struct kbdiacr));
>  			if (IS_ERR(dia))
>  				return PTR_ERR(dia);
>  
> @@ -1811,8 +1811,8 @@ int vt_do_diacrit(unsigned int cmd, void __user *udp, int perm)
>  			return -EINVAL;

Ditto.

>  		if (ct) {
> -			buf = memdup_user(a->kbdiacruc,
> -					  ct * sizeof(struct kbdiacruc));
> +			buf = memdup_array_user(a->kbdiacruc,
> +						ct, sizeof(struct kbdiacruc));