lkml.org 
[lkml]   [2015]   [Oct]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 08/13] lib/test_printf.c: check for out-of-bound writes
From
On Wed, Oct 21, 2015 at 5:30 AM, Rasmus Villemoes
<linux@rasmusvillemoes.dk> wrote:
> Add a few padding bytes on either side of the test buffer, and check
> that these (and the part of the buffer not used) are untouched by
> vsnprintf.
>
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>

Cool, I like this. :)

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> lib/test_printf.c | 24 +++++++++++++++++++-----
> 1 file changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/lib/test_printf.c b/lib/test_printf.c
> index 9232a2add28c..1ce1a1dd8faf 100644
> --- a/lib/test_printf.c
> +++ b/lib/test_printf.c
> @@ -16,6 +16,7 @@
> #include <linux/in.h>
>
> #define BUF_SIZE 256
> +#define PAD_SIZE 16
> #define FILL_CHAR '$'
>
> #define PTR1 ((void*)0x01234567)
> @@ -39,6 +40,7 @@
> static unsigned total_tests __initdata;
> static unsigned failed_tests __initdata;
> static char *test_buffer __initdata;
> +static char *alloced_buffer __initdata;
>
> static int __printf(4, 0) __init
> do_test(int bufsize, const char *expect, int elen,
> @@ -49,7 +51,7 @@ do_test(int bufsize, const char *expect, int elen,
>
> total_tests++;
>
> - memset(test_buffer, FILL_CHAR, BUF_SIZE);
> + memset(alloced_buffer, FILL_CHAR, BUF_SIZE + 2*PAD_SIZE);
> va_copy(aq, ap);
> ret = vsnprintf(test_buffer, bufsize, fmt, aq);
> va_end(aq);
> @@ -60,8 +62,13 @@ do_test(int bufsize, const char *expect, int elen,
> return 1;
> }
>
> + if (memchr_inv(alloced_buffer, FILL_CHAR, PAD_SIZE)) {
> + pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote before buffer\n", bufsize, fmt);
> + return 1;
> + }
> +
> if (!bufsize) {
> - if (memchr_inv(test_buffer, FILL_CHAR, BUF_SIZE)) {
> + if (memchr_inv(test_buffer, FILL_CHAR, BUF_SIZE + PAD_SIZE)) {
> pr_warn("vsnprintf(buf, 0, \"%s\", ...) wrote to buffer\n",
> fmt);
> return 1;
> @@ -76,6 +83,12 @@ do_test(int bufsize, const char *expect, int elen,
> return 1;
> }
>
> + if (memchr_inv(test_buffer + written + 1, FILL_CHAR, BUF_SIZE + PAD_SIZE - (written + 1))) {
> + pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote beyond the nul-terminator\n",
> + bufsize, fmt);
> + return 1;
> + }
> +
> if (memcmp(test_buffer, expect, written)) {
> pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote '%s', expected '%.*s'\n",
> bufsize, fmt, test_buffer, written, expect);
> @@ -342,16 +355,17 @@ test_pointer(void)
> static int __init
> test_printf_init(void)
> {
> - test_buffer = kmalloc(BUF_SIZE, GFP_KERNEL);
> - if (!test_buffer)
> + alloced_buffer = kmalloc(BUF_SIZE + 2*PAD_SIZE, GFP_KERNEL);
> + if (!alloced_buffer)
> return -ENOMEM;
> + test_buffer = alloced_buffer + PAD_SIZE;
>
> test_basic();
> test_number();
> test_string();
> test_pointer();
>
> - kfree(test_buffer);
> + kfree(alloced_buffer);
>
> if (failed_tests == 0)
> pr_info("all %u tests passed\n", total_tests);
> --
> 2.6.1
>



--
Kees Cook
Chrome OS Security


\
 
 \ /
  Last update: 2015-10-26 08:01    [W:0.034 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site