linux-kernel - Re: [RFC PATCH] kernel/panic: Filter out a potential trailing newline

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Date:   Wed, 10 Oct 2018 08:00:02 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>, x86@...nel.org
Subject: Re: [RFC PATCH] kernel/panic: Filter out a potential trailing newline


* Borislav Petkov <bp@...en8.de> wrote:

> From: Borislav Petkov <bp@...e.de>
> 
> If a call to panic() terminates the string with a \n, the result puts
> the closing brace ']---' on a newline because panic() itself adds \n
> too.
> 
> Now, if one goes and removes the newline chars from all panic()
> invocations - and the stats right now look like this:
> 
> ~300 calls with an \n
> ~500 calls without a \n
> 
> one is destined to a neverending game of whack-a-mole because the usual
> thing to do is add a newline at the end of a string a function is
> supposed to print.
> 
> Therefore, simply zap any \n at the end of the panic string to avoid
> touching so many places in the kernel.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> Cc: x86@...nel.org
> ---
>  kernel/panic.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 8b2e002d52eb..5776d2879650 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -136,7 +136,7 @@ void panic(const char *fmt, ...)
>  {
>  	static char buf[1024];
>  	va_list args;
> -	long i, i_next = 0;
> +	long i, i_next = 0, len;
>  	int state = 0;
>  	int old_cpu, this_cpu;
>  	bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;
> @@ -173,8 +173,12 @@ void panic(const char *fmt, ...)
>  	console_verbose();
>  	bust_spinlocks(1);
>  	va_start(args, fmt);
> -	vsnprintf(buf, sizeof(buf), fmt, args);
> +	len = vscnprintf(buf, sizeof(buf), fmt, args);
>  	va_end(args);
> +
> +	if (len && buf[len - 1] == '\n')
> +		buf[len - 1] = '\0';

Nice, this patch saves a couple of hundred trivial upstream commits in the next 20 years:

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo