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

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Date:   Fri, 11 Jun 2021 23:40:09 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Jia He <justin.he@....com>, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Eric Biggers <ebiggers@...gle.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFCv3 3/3] lib/test_printf: add test cases for '%pD'

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