linux-kernel - Re: [PATCH v3] vsprintf: Prevent crash when dereferencing invalid pointers

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:   Thu, 15 Mar 2018 16:58:42 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v3] vsprintf: Prevent crash when dereferencing invalid
 pointers

On (03/14/18 15:09), Petr Mladek wrote:
[..]
> +static const char *check_pointer_access(const void *ptr)
> +{
> +	unsigned char byte;
> +
> +	if (!ptr)
> +		return "(null)";
> +
> +	if (probe_kernel_read(&byte, ptr, 1))
                                        ^^^^^
Why one byte? 			     sizeof(ptr)?

[..]
>  char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  	      struct printf_spec spec)
>  {
> +	static const char data_access_fmt[] = "RrhbMmIiEUVNadCDgGO";
>  	const int default_width = 2 * sizeof(void *);
> +	const char *err_msg = NULL;
> +
> +	/* Prevent silent crash when this is called under logbuf_lock. */
> +	if (*fmt && strchr(data_access_fmt, *fmt) != NULL)
> +		err_msg = check_pointer_access(ptr);

Agree with Rasmus, I think switch() is easier.

	-ss