linux-kernel - Re: [PATCH v4 12/20] vsprintf: add new `%pA` format specifier

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Message-ID: <CANiq72mVsvfdyw8=OtSVbZqm43kjnH2+fUg40_j96BkdM0RtVQ@mail.gmail.com>
Date:   Mon, 14 Feb 2022 15:04:47 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Gary Guo <gary@...yguo.net>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v4 12/20] vsprintf: add new `%pA` format specifier

On Mon, Feb 14, 2022 at 12:37 PM David Laight <David.Laight@...lab.com> wrote:
>
> Doesn't that stand a reasonable chance of blowing the kernel stack?
>
> vsnprintf() is likely to be on the 'worst case' stack path anyway.
> Anything vaguely like a recursive call, or anything 'stack expensive'
> inside vsnprintf() stands a real chance of overflowing the stack.

There should be no recursion going on, but stack usage could be a
concern depending on what the formatted types attempt to do (thus we
need to be mindful when implementing `Display`) and what the compiler
could possibly generate on a worst case (Gary, bjorn3 et. al. may want
to give details about this).

Cheers,
Miguel