linux-kernel - Re: [PATCH v1] IMA: pre-allocate buffer to hold keyrings string

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Date:   Thu, 16 Jan 2020 20:17:06 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        linux-integrity@...r.kernel.org
Cc:     sashal@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] IMA: pre-allocate buffer to hold keyrings string

Hi Lakshmi,

Trimming the Cc list. This patch is limited to IMA. 

On Thu, 2020-01-16 at 15:46 -0800, Lakshmi Ramasubramanian wrote:

>  
> @@ -949,6 +949,7 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  	bool uid_token;
>  	struct ima_template_desc *template_desc;
>  	int result = 0;
> +	size_t keyrings_len;
>  
>  	ab = integrity_audit_log_start(audit_context(), GFP_KERNEL,
>  				       AUDIT_INTEGRITY_POLICY_RULE);
> @@ -1114,14 +1115,47 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  		case Opt_keyrings:
>  			ima_log_string(ab, "keyrings", args[0].from);
>  
> +			keyrings_len = strlen(args[0].from) + 1;
> +
>  			if ((entry->keyrings) ||
>  			    (entry->action != MEASURE) ||
> -			    (entry->func != KEY_CHECK)) {
> +			    (entry->func != KEY_CHECK) ||
> +			    (keyrings_len < 2)) {
>  				result = -EINVAL;
>  				break;
>  			}
> +
> +			if (ima_keyrings) {
> +				if (keyrings_len > ima_keyrings_len) {
> +					char *tmpbuf;
> +
> +					tmpbuf = krealloc(ima_keyrings,
> +							  keyrings_len,
> +							  GFP_KERNEL);
> +					if (!tmpbuf) {
> +						result = -ENOMEM;
> +						break;
> +					}
> +
> +					ima_keyrings = tmpbuf;
> +					ima_keyrings_len = keyrings_len;
> +				}
> +			} else {
> +				ima_keyrings = kzalloc(keyrings_len,
> +						       GFP_KERNEL);
> +				if (!ima_keyrings) {
> +					result = -ENOMEM;
> +					break;
> +				}
> +
> +				ima_keyrings_len = keyrings_len;
> +			}

The first time this code is executed ima_keyrings_len is 0.  So "if
(ima_keyrings_len < keyring_len)" will be true.  There's no reason to
differentiate between the first time or subsequent times this code is
executed.  In both cases, krealloc() can be used. 

Mimi


> +
>  			entry->keyrings = kstrdup(args[0].from, GFP_KERNEL);
>  			if (!entry->keyrings) {
> +				kfree(ima_keyrings);
> +				ima_keyrings = NULL;
> +				ima_keyrings_len = 0;
>  				result = -ENOMEM;
>  				break;
>  			}