Re: [PATCH RFCv3 3/3] lib/test_printf: add test cases for '%pD'

From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Jia He <justin.he@arm.com>, Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: "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
Subject: Re: [PATCH RFCv3 3/3] lib/test_printf: add test cases for '%pD'
Date: Fri, 11 Jun 2021 23:40:09 +0200	[thread overview]
Message-ID: <4fe3621f-f4a0-2a74-e831-dad9e046f392@rasmusvillemoes.dk> (raw)
In-Reply-To: <20210611155953.3010-4-justin.he@arm.com>

On 11/06/2021 17.59, Jia He wrote:
> After the behaviour of specifier '%pD' is changed to print full path
> of struct file, the related test cases are also updated.
> 
> Given the string is prepended from the end of the buffer, the check
> of "wrote beyond the nul-terminator" should be skipped.

Sorry, that is far from enough justification.

I should probably have split the "wrote beyond nul-terminator" check in two:

One that checks whether any memory beyond the buffer given to
vsnprintf() was touched (including all the padding, but possibly more
for the cases where we pass a known-too-short buffer), symmetric to the
"wrote before buffer" check.

And then another that checks the area between the '\0' and the end of
the given buffer - I suppose that it's fair game for vsnprintf to use
all of that as scratch space, and for that it could be ok to add that
boolean knob.

Rasmus