linux-kernel - Re: [PATCH v2 1/2] crypto: asymmetric_keys - prevent overflow in asymmetric_key_generate

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Message-Id: <4AF8BE0F-D400-4020-A8F6-EF61A797A24E@linux.dev>
Date: Mon, 13 Oct 2025 10:23:01 +0200
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Lukas Wunner <lukas@...ner.de>
Cc: David Howells <dhowells@...hat.com>,
 Ignat Korchagin <ignat@...udflare.com>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 "David S. Miller" <davem@...emloft.net>,
 Vivek Goyal <vgoyal@...hat.com>,
 stable@...r.kernel.org,
 keyrings@...r.kernel.org,
 linux-crypto@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] crypto: asymmetric_keys - prevent overflow in
 asymmetric_key_generate_id

On 13. Oct 2025, at 08:24, Lukas Wunner wrote:
> On Sun, Oct 12, 2025 at 10:38:40PM +0200, Thorsten Blum wrote:
>> +++ b/crypto/asymmetric_keys/asymmetric_type.c
>> @@ -141,12 +142,14 @@ struct asymmetric_key_id *asymmetric_key_generate_id(const void *val_1,
>> 						     size_t len_2)
>> {
>> 	struct asymmetric_key_id *kid;
>> +	size_t len;
>> 
>> -	kid = kmalloc(sizeof(struct asymmetric_key_id) + len_1 + len_2,
>> -		      GFP_KERNEL);
>> +	if (check_add_overflow(len_1, len_2, &len))
>> +		return ERR_PTR(-EOVERFLOW);
>> +	kid = kmalloc(struct_size(kid, data, len), GFP_KERNEL);
> 
> This will add (at least) 2 bytes to len (namely the size of struct
> asymmetric_key_id)) and may cause an overflow (even if len_1 + len_2
> did not overflow).

Could you explain which part adds "(at least) 2 bytes to len"?

Thanks,
Thorsten