linux-kernel - Re: [PATCH v7 02/10] vsprintf: Consistent %pK handling for kptr

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]

Message-ID: <20190417094430.6a490eee@gandalf.local.home>
Date:   Wed, 17 Apr 2019 09:44:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v7 02/10] vsprintf: Consistent %pK handling for
 kptr_restrict == 0

On Wed, 17 Apr 2019 13:53:42 +0200
Petr Mladek <pmladek@...e.com> wrote:

> restricted_pointer() pretends that it prints the address when kptr_restrict
> is set to zero. But it is never called in this situation. Instead,
> pointer() falls back to ptr_to_id() and hashes the pointer.
> 
> This patch removes the potential confusion. klp_restrict is checked only
> in restricted_pointer().
> 
> It actually fixes a small race when the address might get printed unhashed:
> 
> CPU0                            CPU1
> 
> pointer()
>   if (!kptr_restrict)
>      /* for example set to 2 */
>   restricted_pointer()
> 				/* echo 0 >/proc/sys/kernel/kptr_restrict */
> 				proc_dointvec_minmax_sysadmin()
> 				  klpr_restrict = 0;
>     switch(kptr_restrict)
>       case 0:
> 	break:
> 
>     number()
> 
> Fixes: commit ef0010a30935de4e0211 ("vsprintf: don't use 'restricted_pointer()' when not restricting")
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Tobin Harding <me@...in.cc>
> Cc: Kees Cook <keescook@...omium.org>
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> ---
>  lib/vsprintf.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index eb7b4a06e1f0..2af48948a973 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -725,8 +725,8 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
>  {
>  	switch (kptr_restrict) {
>  	case 0:
> -		/* Always print %pK values */
> -		break;
> +		/* Handle as %p, hash and do _not_ leak addresses. */
> +		return ptr_to_id(buf, end, ptr, spec);
>  	case 1: {
>  		const struct cred *cred;
>  
> @@ -2041,8 +2041,6 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  			return buf;
>  		}
>  	case 'K':
> -		if (!kptr_restrict)
> -			break;
>  		return restricted_pointer(buf, end, ptr, spec);
>  	case 'N':
>  		return netdev_bits(buf, end, ptr, spec, fmt);