linux-kernel - Re: [PATCH 2/2] Yama: add PTRACE exception tracking

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 29 Jun 2010 22:56:09 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Yama: add PTRACE exception tracking

Quoting Kees Cook (kees.cook@...onical.com):
> Some application suites have external crash handlers that depend on
> being able to use PTRACE to generate crash reports (KDE, Chromium, etc).
> Since the inferior process generally knows the PID of the debugger,
> it can use PR_SET_PTRACER to allow a specific PID and its descendants
> to perform the PTRACE instead of only a direct ancestor.
> 
> Signed-off-by: Kees Cook <kees.cook@...onical.com>
> ---

Hi Kees - very nice, overall.  One little note though:

> @@ -32,27 +204,20 @@ static int yama_ptrace_access_check(struct task_struct *child,
>  {
>  	int rc;
>  
> +	/* If standard caps disallows it, so does Yama.  We should
> +	 * should only tighten restrictions further.
> +	 */
>  	rc = cap_ptrace_access_check(child, mode);

This means that if capable(CAP_SYS_PTRACE) we'll always shortcut
here, so

> -	if (rc != 0)
> +	if (rc)
>  		return rc;
>  
>  	/* require ptrace target be a child of ptracer on attach */
> -	if (mode == PTRACE_MODE_ATTACH && ptrace_scope &&
> -	    !capable(CAP_SYS_PTRACE)) {
> -		struct task_struct *walker = child;
> -
> -		rcu_read_lock();
> -		read_lock(&tasklist_lock);
> -		while (walker->pid > 0) {
> -			if (walker == current)
> -				break;
> -			walker = walker->real_parent;
> -		}
> -		if (walker->pid == 0)
> -			rc = -EPERM;
> -		read_unlock(&tasklist_lock);
> -		rcu_read_unlock();
> -	}
> +	if (mode == PTRACE_MODE_ATTACH &&
> +	    ptrace_scope &&
> +	    !capable(CAP_SYS_PTRACE) &&

You don't need the CAP_SYS_PTRACE check here AFAICS.

> +	    !task_is_descendant(current, child) &&
> +	    !ptracer_exception_found(current, child))
> +		rc = -EPERM;
>  
>  	if (rc) {
>  		char name[sizeof(current->comm)];
> @@ -170,6 +335,8 @@ static struct security_operations yama_ops = {
>  	.ptrace_access_check =	yama_ptrace_access_check,
>  	.inode_follow_link =	yama_inode_follow_link,
>  	.path_link =		yama_path_link,
> +	.task_prctl =		yama_task_prctl,
> +	.task_free =		yama_task_free,
>  };
>  
>  #ifdef CONFIG_SYSCTL
> @@ -221,6 +388,8 @@ static __init int yama_init(void)
>  
>  	printk(KERN_INFO "Yama: becoming mindful.\n");
>  
> +	spin_lock_init(&ptracer_relations_lock);
> +
>  	if (register_security(&yama_ops))
>  		panic("Yama: kernel registration failed.\n");
>  
> -- 
> 1.7.1
> 
> 
> -- 
> Kees Cook
> Ubuntu Security Team
> --
> To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/