From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Petr Mladek <pmladek@suse.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
"Tobin C . Harding" <me@tobin.cc>, Joe Perches <joe@perches.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 09/11] vsprintf: Prevent crash when dereferencing invalid pointers
Date: Wed, 25 Apr 2018 18:10:54 +0300 [thread overview]
Message-ID: <1524669054.21176.566.camel@linux.intel.com> (raw)
In-Reply-To: <20180425111251.13246-10-pmladek@suse.com>
On Wed, 2018-04-25 at 13:12 +0200, Petr Mladek wrote:
> We already prevent crash when dereferencing some obviously broken
> pointers. But the handling is not consistent. Sometimes we print
> "(null)"
> only for pure NULL pointer, sometimes for pointers in the first
> page and sometimes also for pointers in the last page (error codes).
>
> Note that printk() call this code under logbuf_lock. Any recursive
> printks are redirected to the printk_safe implementation and the
> messages
> are stored into per-CPU buffers. These buffers might be eventually
> flushed
> in printk_safe_flush_on_panic() but it is not guaranteed.
>
> This patch adds a check using probe_kernel_read(). It is not a full-
> proof
> test. But it should help to see the error message in 99% situations
> where
> the kernel would silently crash otherwise.
>
> Also it makes the error handling unified for "%s" and the many %p*
> specifiers that need to read the data from a given address. We print:
>
> + (null) when accessing data on pure pure NULL address
> + (efault) when accessing data on an invalid address
>
> It does not affect the %p* specifiers that just print the given
> address
> in some form, namely %pF, %pf, %pS, %ps, %pB, %pK, %px, and plain %p.
>
> Note that we print (efault) from security reasons. In fact, the real
> address can be seen only by %px or eventually %pK.
> +static const char *check_pointer_access(const void *ptr)
> +{
> + char byte;
> +
> + if (!ptr)
> + return "(null)";
> +
> + if (probe_kernel_address(ptr, byte))
> + return "(efault)";
> +
> + return NULL;
> +}
> +
> +static bool valid_pointer_access(char **buf, char *end, const void
> *ptr,
> + struct printf_spec spec)
> +{
> + const char *err_msg;
> +
> + err_msg = check_pointer_access(ptr);
> + if (err_msg) {
> + *buf = valid_string(*buf, end, err_msg, spec);
> + return false;
> + }
> +
> + return true;
> +}
I would preserve similar style of buf pointer handling, i.e.
static char *valid_pointer_access(char **buf, char *end,
const void *ptr, struct printf_spec spec)
{
const char *err_msg;
err_msg = check_pointer_access(ptr);
if (err_msg)
return = valid_string(*buf, end, err_msg, spec);
return NULL;
}
--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy
next prev parent reply other threads:[~2018-04-25 15:11 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-25 11:12 [PATCH v5 00/11] vsprintf: Prevent silent crashes and consolidate error handling Petr Mladek
2018-04-25 11:12 ` [PATCH v5 01/11] vsprintf: Shuffle misc pointer to string functions Petr Mladek
2018-04-25 14:57 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 02/11] vsprintf: Add missing const ptr qualifier to prt_to_id() Petr Mladek
2018-04-25 14:57 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 03/11] vsprintf: Consistent %pK handling for kptr_restrict == 0 Petr Mladek
2018-04-25 14:58 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 04/11] vsprintf: Do not check address of well-known strings Petr Mladek
2018-04-25 11:44 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 05/11] vsprintf: Consolidate handling of unknown pointer specifiers Petr Mladek
2018-04-25 13:08 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 06/11] vsprintf: Factor out %p[iI] handler as ip_addr_string() Petr Mladek
2018-04-25 13:11 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 07/11] vsprintf: Factor out %pV handler as va_format() Petr Mladek
2018-04-25 14:56 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 08/11] vsprintf: Factor out %pO handler as kobject_string() Petr Mladek
2018-04-25 15:01 ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 09/11] vsprintf: Prevent crash when dereferencing invalid pointers Petr Mladek
2018-04-25 15:10 ` Andy Shevchenko [this message]
2018-04-25 15:32 ` Andy Shevchenko
2018-04-27 12:47 ` Petr Mladek
2018-05-03 11:55 ` Andy Shevchenko
2018-04-26 21:46 ` kbuild test robot
2018-04-25 11:12 ` [PATCH v5 10/11] vsprintf: WARN() on invalid pointer access Petr Mladek
2018-04-25 12:43 ` Rasmus Villemoes
2018-04-26 1:28 ` Sergey Senozhatsky
2018-04-27 12:37 ` Petr Mladek
2018-04-25 11:12 ` [PATCH v5 11/11] vsprintf: Avoid confusion between invalid address and value Petr Mladek
2018-04-27 14:10 ` [PATCH v5 00/11] vsprintf: Prevent silent crashes and consolidate error handling Petr Mladek
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