linux-kernel - Re: [RFC PATCH 1/1] vsprintf: Warn on integer scanning overflows

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Message-ID: <ZIHlZsPMZ2dI5/yG@smile.fi.intel.com>
Date:   Thu, 8 Jun 2023 17:27:50 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Richard Weinberger <richard@....at>
Cc:     linux-hardening@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, keescook@...omium.org,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [RFC PATCH 1/1] vsprintf: Warn on integer scanning overflows

On Thu, Jun 08, 2023 at 12:37:55AM +0200, Richard Weinberger wrote:
> The scanf function family has no way to indicate overflows
> while scanning. As consequence users of these function have to make
> sure their input cannot cause an overflow.
> Since this is not always the case add WARN_ON_ONCE() guards to
> trigger a warning upon an overflow.

...

>  	if (prefix_chars < max_chars) {
>  		rv = _parse_integer_limit(cp, base, &result, max_chars - prefix_chars);
> +		WARN_ON_ONCE(rv & KSTRTOX_OVERFLOW);

This seems incorrect. simple_strto*() are okay to overflow. It's by design.

>  		/* FIXME */

...and that's why this one is here.

>  		cp += (rv & ~KSTRTOX_OVERFLOW);
>  	} else {


-- 
With Best Regards,
Andy Shevchenko