linux-kernel - Re: [PATCH 06/20] ima: Manual replacement of the deprecated strlcpy() with return values

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Message-ID: <1a679c59345b02f10e425c8c5c55efd901dc714d.camel@linux.ibm.com>
Date:   Tue, 02 Mar 2021 08:29:58 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Romain Perier <romain.perier@...il.com>,
        Kees Cook <keescook@...omium.org>,
        kernel-hardening@...ts.openwall.com,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/20] ima: Manual replacement of the deprecated
 strlcpy() with return values

On Mon, 2021-02-22 at 16:12 +0100, Romain Perier wrote:
> The strlcpy() reads the entire source buffer first, it is dangerous if
> the source buffer lenght is unbounded or possibility non NULL-terminated.

As other's have pointed out, "lenght" -> length.

> It can lead to linear read overflows, crashes, etc...
> 
> As recommended in the deprecated interfaces [1], it should be replaced
> by strscpy.
> 
> This commit replaces all calls to strlcpy that handle the return values
> by the corresponding strscpy calls with new handling of the return
> values (as it is quite different between the two functions).
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> 
> Signed-off-by: Romain Perier <romain.perier@...il.com>
> ---
>  security/integrity/ima/ima_policy.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 9b45d064a87d..1a905b8b064f 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -790,8 +790,14 @@ static int __init ima_init_arch_policy(void)
>  	for (rules = arch_rules, i = 0; *rules != NULL; rules++) {
>  		char rule[255];
>  		int result;
> +		ssize_t len;
>  
> -		result = strlcpy(rule, *rules, sizeof(rule));
> +		len = strscpy(rule, *rules, sizeof(rule));
> +		if (len == -E2BIG) {
> +			pr_warn("Internal copy of architecture policy rule '%s' "
> +				"failed. Skipping.\n", *rules);

"arch_rules" is an array of hard coded strings.   The generic reason
for replacing strlcpy with strscpy doesn't seem applicable; however,
the additonal warning is appropriate.

(User-visible strings are not bound to the 80 column length.  Breaking
up the line like this is fine, but unnecessary.)

Acked-by: Mimi Zohar <zohar@...ux.ibm.com>

thanks,

Mimi

> +			continue;
> +		}
>  
>  		INIT_LIST_HEAD(&arch_policy_entry[i].list);
>  		result = ima_parse_rule(rule, &arch_policy_entry[i]);
>