linux-kernel - Re: [PATCH v2] KEYS: prevent NULL pointer dereference in find_asymmetric

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Message-Id: <D42N9ASJJSUD.EG094MFWZA4Q@kernel.org>
Date: Tue, 10 Sep 2024 16:38:37 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Roman Smirnov" <r.smirnov@....ru>, "David Howells"
 <dhowells@...hat.com>, "Herbert Xu" <herbert@...dor.apana.org.au>, "David
 S. Miller" <davem@...emloft.net>, "Andrew Zaborowski"
 <andrew.zaborowski@...el.com>
Cc: <keyrings@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>, "Sergey
 Shtylyov" <s.shtylyov@....ru>
Subject: Re: [PATCH v2] KEYS: prevent NULL pointer dereference in
 find_asymmetric_key()

On Tue Sep 10, 2024 at 2:18 PM EEST, Roman Smirnov wrote:
> In find_asymmetric_key(), if all NULLs are passed in id_{0,1,2} parameters
> the kernel will first emit WARN and then have an oops because id_2 gets
> dereferenced anyway.
>
> Found by Linux Verification Center (linuxtesting.org) with Svace static
> analysis tool.

Weird, I recall that I've either sent a patch to address the same site
OR have commented a patch with similar reasoning. Well, it does not
matter, I think it this makes sense to me.

You could further add to the motivation that given the panic_on_warn
kernel command-line parameter, it is for the best limit the scope and
use of the WARN-macro.

>
> Fixes: 7d30198ee24f ("keys: X.509 public key issuer lookup without AKID")

I would still call this an improvement. It overuses warn but I don't
think this a bug. 

> Suggested-by: Sergey Shtylyov <s.shtylyov@....ru>
> Signed-off-by: Roman Smirnov <r.smirnov@....ru>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>
> ---
>  crypto/asymmetric_keys/asymmetric_type.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
> index a5da8ccd353e..43af5fa510c0 100644
> --- a/crypto/asymmetric_keys/asymmetric_type.c
> +++ b/crypto/asymmetric_keys/asymmetric_type.c
> @@ -60,17 +60,18 @@ struct key *find_asymmetric_key(struct key *keyring,
>  	char *req, *p;
>  	int len;
>  
> -	WARN_ON(!id_0 && !id_1 && !id_2);
> -
>  	if (id_0) {
>  		lookup = id_0->data;
>  		len = id_0->len;
>  	} else if (id_1) {
>  		lookup = id_1->data;
>  		len = id_1->len;
> -	} else {
> +	} else if (id_2) {
>  		lookup = id_2->data;
>  		len = id_2->len;
> +	} else {
> +		WARN_ON(1);

This is totally fine. It is an improvement to the current situation.

> +		return ERR_PTR(-EINVAL);
>  	}
>  
>  	/* Construct an identifier "id:<keyid>". */

Can be applied as an improvement and with the added bits about
panic_on_warn to the commit message.

BR, Jarkko