linux-kernel - Re: [PATCH] x86, mce: Fix stack out-of-bounds write in mce-inject.c:flags

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Message-ID: <20180427165939.GG15229@pd.tnic>
Date:   Fri, 27 Apr 2018 18:59:39 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-edac@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, mce: Fix stack out-of-bounds write in
 mce-inject.c:flags_read()

On Fri, Apr 27, 2018 at 09:37:08AM -0700, Luck, Tony wrote:
> Each of the strings that we want to put into the buf[MAX_FLAG_OPT_SIZE]
> in flags_read() is two characters. But the sprintf() adds a trailing newline
> and will add a terminating NUL byte. So MAX_FLAG_OPT_SIZE needs to be 4.

... and I dumped the n here:

	n = sprintf(buf, "%s\n", flags_options[inj_type])

and it was 3 but sprintf() calls vsnprintf() and *that* does return:

" * The return value is the number of characters which would
 * be generated for the given input, excluding the trailing
 * '\0', as per ISO C99."

So I'll extend the commit message with that and apply it.

Thanks.

-- 
Regards/Gruss,
    Boris.

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