From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
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 v6 8/9] vsprintf: Prevent crash when dereferencing invalid pointers
Date: Tue, 19 Feb 2019 12:30:03 +0900 [thread overview]
Message-ID: <20190219033003.GA2284@jagdpanzerIV> (raw)
In-Reply-To: <20190208152310.29531-9-pmladek@suse.com>
On (02/08/19 16:23), Petr Mladek wrote:
[..]
> + /*
> + * This is not a fool-proof test. 99% of the time that this will fault is
> + * due to a bad pointer, not one that crosses into bad memory. Just test
> + * the address to make sure it doesn't fault due to a poorly added printk
> + * during debugging.
> + */
> +static const char *check_pointer_msg(const void *ptr)
> +{
> + char byte;
> +
> + if (!ptr)
> + return "(null)";
> +
> + if (probe_kernel_address(ptr, byte))
> + return "(efault)";
> +
> + return NULL;
> +}
Hmm... So the assumption here is that the target buffer always has
at least strlen("(efault)") bytes and, thus, we always can write the
error message to it.
> +static int check_pointer(char **buf, char *end, const void *ptr,
> + struct printf_spec spec)
> +{
> + const char *err_msg;
> +
> + err_msg = check_pointer_msg(ptr);
> + if (err_msg) {
> + *buf = string_nocheck(*buf, end, err_msg, spec);
> + return -EFAULT;
> + }
> +
> + return 0;
> +}
Suppose in my driver I sprintf() pointers to 4-bytes strings and, thus,
have only 5 spare bytes in target buffer. But one of the pointers is
faulty and now sprintf() writes "(efault)" to target buffer which can
hold only 5 bytes.
-ss
next prev parent reply other threads:[~2019-02-19 3:30 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-08 15:23 [PATCH v6 0/9] vsprintf: Prevent silent crashes and consolidate error handling Petr Mladek
2019-02-08 15:23 ` [PATCH v6 1/9] vsprintf: Shuffle restricted_pointer() Petr Mladek
2019-02-08 15:23 ` [PATCH v6 2/9] vsprintf: Consistent %pK handling for kptr_restrict == 0 Petr Mladek
2019-02-08 15:23 ` [PATCH v6 3/9] vsprintf: Do not check address of well-known strings Petr Mladek
2019-02-08 17:27 ` Andy Shevchenko
2019-02-08 15:23 ` [PATCH v6 4/9] vsprintf: Factor out %p[iI] handler as ip_addr_string() Petr Mladek
2019-02-08 15:23 ` [PATCH v6 5/9] vsprintf: Factor out %pV handler as va_format() Petr Mladek
2019-02-08 17:11 ` Joe Perches
2019-02-12 13:00 ` Petr Mladek
2019-02-12 14:32 ` Steven Rostedt
2019-02-12 17:58 ` Joe Perches
2019-02-12 19:47 ` Steven Rostedt
2019-02-12 20:22 ` Rasmus Villemoes
2019-02-08 15:23 ` [PATCH v6 6/9] vsprintf: Factor out %pO handler as kobject_string() Petr Mladek
2019-02-08 15:23 ` [PATCH v6 7/9] vsprintf: Consolidate handling of unknown pointer specifiers Petr Mladek
2019-02-08 17:25 ` Andy Shevchenko
2019-02-12 13:35 ` Petr Mladek
2019-02-08 15:23 ` [PATCH v6 8/9] vsprintf: Prevent crash when dereferencing invalid pointers Petr Mladek
2019-02-19 3:30 ` Sergey Senozhatsky [this message]
2019-02-19 11:02 ` Andy Shevchenko
2019-02-19 12:51 ` Sergey Senozhatsky
2019-02-19 13:49 ` Andy Shevchenko
2019-02-19 14:15 ` Sergey Senozhatsky
2019-02-20 10:24 ` Petr Mladek
2019-02-08 15:23 ` [PATCH v6 9/9] vsprintf: Avoid confusion between invalid address and value Petr Mladek
2019-02-08 17:27 ` Andy Shevchenko
2019-02-12 15:45 ` Petr Mladek
2019-02-13 13:54 ` Andy Shevchenko
2019-02-14 8:42 ` Petr Mladek
2019-02-14 12:45 ` Andy Shevchenko
2019-02-19 3:03 ` Sergey Senozhatsky
2019-02-19 11:06 ` Andy Shevchenko
2019-02-20 9:24 ` Petr Mladek
2019-02-21 1:47 ` Sergey Senozhatsky
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