From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Jia He <justin.he@arm.com>
Cc: Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Jonathan Corbet <corbet@lwn.net>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Eric Biggers <ebiggers@google.com>,
"Ahmed S. Darwish" <a.darwish@linutronix.de>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org,
Matthew Wilcox <willy@infradead.org>,
Christoph Hellwig <hch@infradead.org>,
nd@arm.com
Subject: Re: [PATCH v2 3/4] lib/test_printf.c: split write-beyond-buffer check in two
Date: Wed, 23 Jun 2021 12:16:08 +0300 [thread overview]
Message-ID: <YNL72KwP8oyNzons@smile.fi.intel.com> (raw)
In-Reply-To: <20210623055011.22916-4-justin.he@arm.com>
On Wed, Jun 23, 2021 at 01:50:10PM +0800, Jia He wrote:
> From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
>
> Before each invocation of vsnprintf(), do_test() memsets the entire
> allocated buffer to a sentinel value. That buffer includes leading and
> trailing padding which is never included in the buffer area handed to
> vsnprintf (spaces merely for clarity):
>
> pad test_buffer pad
> **** **************** ****
>
> Then vsnprintf() is invoked with a bufsize argument <=
> BUF_SIZE. Suppose bufsize=10, then we'd have e.g.
>
> |pad | test_buffer |pad |
> **** pizza0 **** ****** ****
> A B C D E
>
> where vsnprintf() was given the area from B to D.
>
> It is obviously a bug for vsnprintf to touch anything between A and B
> or between D and E. The former is checked for as one would expect. But
> for the latter, we are actually a little stricter in that we check the
> area between C and E.
>
> Split that check in two, providing a clearer error message in case it
> was a genuine buffer overrun and not merely a write within the
> provided buffer, but after the end of the generated string.
>
> So far, no part of the vsnprintf() implementation has had any use for
> using the whole buffer as scratch space, but it's not unreasonable to
> allow that, as long as the result is properly nul-terminated and the
> return value is the right one. However, it is somewhat unusual, and
> most %<something> won't need this, so keep the [C,D] check, but make
> it easy for a later patch to make that part opt-out for certain tests.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Tested-by: Jia He <justin.he@arm.com>
> Signed-off-by: Jia He <justin.he@arm.com>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> ---
> lib/test_printf.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/lib/test_printf.c b/lib/test_printf.c
> index ec0d5976bb69..d1d2f898ebae 100644
> --- a/lib/test_printf.c
> +++ b/lib/test_printf.c
> @@ -78,12 +78,17 @@ 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))) {
> + if (memchr_inv(test_buffer + written + 1, FILL_CHAR, bufsize - (written + 1))) {
> pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote beyond the nul-terminator\n",
> bufsize, fmt);
> return 1;
> }
>
> + if (memchr_inv(test_buffer + bufsize, FILL_CHAR, BUF_SIZE + PAD_SIZE - bufsize)) {
> + pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote beyond buffer\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);
> --
> 2.17.1
>
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2021-06-23 9:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-23 5:50 [PATCH v2 0/4] make '%pD' print the full path of file Jia He
2021-06-23 5:50 ` [PATCH v2 1/4] fs: introduce helper d_path_unsafe() Jia He
2021-06-23 9:10 ` Andy Shevchenko
2021-06-24 5:48 ` Justin He
2021-07-14 8:33 ` Justin He
2021-07-14 9:17 ` Andy Shevchenko
2021-06-28 5:13 ` Justin He
2021-06-28 9:06 ` Petr Mladek
2021-07-02 6:36 ` Justin He
2021-06-23 5:50 ` [PATCH v2 2/4] lib/vsprintf.c: make '%pD' print the full path of file Jia He
2021-06-23 9:14 ` Andy Shevchenko
2021-06-24 9:01 ` Petr Mladek
2021-06-24 10:49 ` Andy Shevchenko
2021-06-25 2:29 ` Justin He
2021-06-25 2:32 ` Justin He
2021-06-23 5:50 ` [PATCH v2 3/4] lib/test_printf.c: split write-beyond-buffer check in two Jia He
2021-06-23 9:16 ` Andy Shevchenko [this message]
2021-06-23 5:50 ` [PATCH v2 4/4] lib/test_printf.c: add test cases for '%pD' Jia He
2021-06-23 9:17 ` [PATCH v2 0/4] make '%pD' print the full path of file Andy Shevchenko
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