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From: Petr Mladek <pmladek@suse.com>
To: Jia He <justin.he@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	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>
Subject: Re: [PATCH RFCv4 3/4] lib/test_printf.c: split write-beyond-buffer check in two
Date: Thu, 17 Jun 2021 16:17:21 +0200	[thread overview]
Message-ID: <YMtZcVy4gvmMtYv+@alley> (raw)
In-Reply-To: <20210615154952.2744-4-justin.he@arm.com>

On Tue 2021-06-15 23:49:51, 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.

Excellent commit message.

> 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>

Best Regards,
Petr

  reply	other threads:[~2021-06-17 14:17 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-15 15:49 [PATCH RFCv4 0/4] make '%pD' print full path for file Jia He
2021-06-15 15:49 ` [PATCH RFCv4 1/4] fs: introduce helper d_path_unsafe() Jia He
2021-06-15 20:40   ` Andy Shevchenko
2021-06-16  0:54     ` Justin He
2021-06-15 15:49 ` [PATCH RFCv4 2/4] lib/vsprintf.c: make '%pD' print full path for file Jia He
2021-06-15 20:44   ` Andy Shevchenko
2021-06-17 14:09   ` Petr Mladek
2021-06-22  2:20     ` Justin He
2021-06-15 15:49 ` [PATCH RFCv4 3/4] lib/test_printf.c: split write-beyond-buffer check in two Jia He
2021-06-17 14:17   ` Petr Mladek [this message]
2021-06-15 15:49 ` [PATCH RFCv4 4/4] lib/test_printf.c: add test cases for '%pD' Jia He
2021-06-15 20:47   ` Andy Shevchenko
2021-06-17 14:52     ` Petr Mladek
2021-06-22  2:21       ` Justin He
2021-06-15 20:42 ` [PATCH RFCv4 0/4] make '%pD' print full path for file Andy Shevchenko
2021-06-16  5:09 ` Christoph Hellwig
2021-06-16  5:16   ` Justin He

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