linux-kernel - Re: [PATCH] consolemap: Fix a memory leaking bug in drivers/tty/vt/consolemap.c

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Date:   Tue, 21 May 2019 13:44:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Gen Zhang <blackgod016574@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] consolemap: Fix a memory leaking bug in
 drivers/tty/vt/consolemap.c

On Tue, May 21, 2019 at 05:29:35PM +0800, Gen Zhang wrote:
> In function con_insert_unipair(), when allocation for p2 and p1[n]
> fails, ENOMEM is returned, but previously allocated p1 is not freed, 
> remains as leaking memory. Thus we should free p1 as well when this
> allocation fails.
> 
> Signed-off-by: Gen Zhang <blackgod016574@...il.com>
> 
> ---
> diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
> index b28aa0d..47fbd73 100644
> --- a/drivers/tty/vt/consolemap.c
> +++ b/drivers/tty/vt/consolemap.c
> @@ -489,7 +489,10 @@ con_insert_unipair(struct uni_pagedir *p, u_short unicode, u_short fontpos)
>  	p2 = p1[n = (unicode >> 6) & 0x1f];
>  	if (!p2) {
>  		p2 = p1[n] = kmalloc_array(64, sizeof(u16), GFP_KERNEL);
> -		if (!p2) return -ENOMEM;
> +		if (!p2) {
> +			kfree(p1);
> +			return -ENOMEM;
> +		}

This doesn't look safe to me: p->uni_pgdir[n] will still have a handle
to the freed memory, won't it?

(And please direct these patches to Greg, as he's the current
maintainer; I'm happy to stay CCed, of course.)

-Kees

>  		memset(p2, 0xff, 64*sizeof(u16)); /* No glyphs for the characters (yet) */
>  	}
>  

-- 
Kees Cook