linux-kernel - Re: [PATCH] apparmor: Replace sprintf/strcpy with scnprintf/strscpy in aa_policy

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Message-ID: <aOvEQVqYUnMXrMxI@mail.hallyn.com>
Date: Sun, 12 Oct 2025 10:07:45 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: John Johansen <john.johansen@...onical.com>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	linux-hardening@...r.kernel.org, apparmor@...ts.ubuntu.com,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] apparmor: Replace sprintf/strcpy with scnprintf/strscpy
 in aa_policy_init

On Sat, Oct 11, 2025 at 06:46:46PM +0200, Thorsten Blum wrote:
> strcpy() is deprecated and sprintf() does not perform bounds checking
> either. Although an overflow is unlikely, it's better to proactively
> avoid it by using the safer strscpy() and scnprintf(), respectively.
> 
> Additionally, unify memory allocation for 'hname' to simplify and
> improve aa_policy_init().
> 
> Link: https://github.com/KSPP/linux/issues/88
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>

Reviewed-by: Serge Hallyn <serge@...lyn.com>

> ---
>  security/apparmor/lib.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/security/apparmor/lib.c b/security/apparmor/lib.c
> index 82dbb97ad406..acf7f5189bec 100644
> --- a/security/apparmor/lib.c
> +++ b/security/apparmor/lib.c
> @@ -478,19 +478,17 @@ bool aa_policy_init(struct aa_policy *policy, const char *prefix,
>  		    const char *name, gfp_t gfp)
>  {
>  	char *hname;
> +	size_t hname_sz;
>  
> +	hname_sz = (prefix ? strlen(prefix) + 2 : 0) + strlen(name) + 1;
>  	/* freed by policy_free */
> -	if (prefix) {
> -		hname = aa_str_alloc(strlen(prefix) + strlen(name) + 3, gfp);
> -		if (hname)
> -			sprintf(hname, "%s//%s", prefix, name);
> -	} else {
> -		hname = aa_str_alloc(strlen(name) + 1, gfp);
> -		if (hname)
> -			strcpy(hname, name);
> -	}
> +	hname = aa_str_alloc(hname_sz, gfp);
>  	if (!hname)
>  		return false;
> +	if (prefix)
> +		scnprintf(hname, hname_sz, "%s//%s", prefix, name);
> +	else
> +		strscpy(hname, name, hname_sz);
>  	policy->hname = hname;
>  	/* base.name is a substring of fqname */
>  	policy->name = basename(policy->hname);
> -- 
> 2.51.0