linux-kernel - Re: [PATCH v2] consolemap: Fix a memory leaking bug in drivers/tty/vt/consolemap.c

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Message-ID: <b99d0da6-a1d6-1c04-66ff-b2937d21d346@nvidia.com>
Date:   Fri, 24 May 2019 10:37:59 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Kees Cook <keescook@...omium.org>,
        Gen Zhang <blackgod016574@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     <jslaby@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] consolemap: Fix a memory leaking bug in
 drivers/tty/vt/consolemap.c

Kees,

On 23/05/2019 17:54, Kees Cook wrote:
> On Thu, May 23, 2019 at 08:34:52AM +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>
> 
> As far as I can see this is correct, as it's just restoring the prior
> state before the p1 allocation.

Are you sure this is correct? It looks like p1 is only allocated if
p->uni_pgdir[n = unicode >> 11] == NULL.

I only mention this because I have seen a few patches from Gen today
regarding memory leaks and devm_kzalloc() that are not correct.

> Reviewed-by: Kees Cook <keescook@...omium.org>
> 
>> ---
>> diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
>> index b28aa0d..79fcc96 100644
>> --- a/drivers/tty/vt/consolemap.c
>> +++ b/drivers/tty/vt/consolemap.c
>> @@ -489,7 +489,11 @@ 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);
>> +			p->uni_pgdir[n] = NULL;
>> +			return -ENOMEM;
>> +		}
>>  		memset(p2, 0xff, 64*sizeof(u16)); /* No glyphs for the characters (yet) */
>>  	}
>>  
>> ---

Cheers
Jon

-- 
nvpublic