linux-kernel - Re: [PATCH v2 1/4] printk/NMI: Handle continuous lines and missing newline

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Date:   Fri, 11 Nov 2016 12:28:51 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <jbacik@...com>, David Sterba <dsterba@...e.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] printk/NMI: Handle continuous lines and missing
 newline

On Wed,  9 Nov 2016 13:41:28 +0100
Petr Mladek <pmladek@...e.com> wrote:


>  /*
> @@ -135,8 +170,8 @@ static void __printk_nmi_flush(struct irq_work *work)
>  		__RAW_SPIN_LOCK_INITIALIZER(read_lock);
>  	struct nmi_seq_buf *s = container_of(work, struct nmi_seq_buf, work);
>  	unsigned long flags;
> -	size_t len, size;
> -	int i, last_i;
> +	size_t len;
> +	int i;
>  
>  	/*
>  	 * The lock has two functions. First, one reader has to flush all
> @@ -154,12 +189,14 @@ static void __printk_nmi_flush(struct irq_work *work)
>  	/*
>  	 * This is just a paranoid check that nobody has manipulated
>  	 * the buffer an unexpected way. If we printed something then
> -	 * @len must only increase.
> +	 * @len must only increase. Also it should never overflow the
> +	 * buffer size.
>  	 */
> -	if (i && i >= len) {
> +	if ((i && i >= len) || len > sizeof(s->buffer)) {

What's wrong with using s->len? Isn't that what is inside the buffer?
Couldn't just checking against the buffer size print garbage?

-- Steve


>  		const char *msg = "printk_nmi_flush: internal error\n";
>  
>  		printk_nmi_flush_line(msg, strlen(msg));
> +		len = 0;
>  	}
>  
>  	if (!len)
> @@ -167,22 +204,7 @@ static void __printk_nmi_flush(struct irq_work *work)
>  
>  	/* Make sure that data has been written up to the @len */
>  	smp_rmb();
> -
> -	size = min(len, sizeof(s->buffer));
> -	last_i = i;
> -
> -	/* Print line by line. */
> -	for (; i < size; i++) {
> -		if (s->buffer[i] == '\n') {
> -			printk_nmi_flush_seq_line(s, last_i, i);
> -			last_i = i + 1;
> -		}
> -	}
> -	/* Check if there was a partial line. */
> -	if (last_i < size) {
> -		printk_nmi_flush_seq_line(s, last_i, size - 1);
> -		printk_nmi_flush_line("\n", strlen("\n"));
> -	}
> +	i += printk_nmi_flush_buffer(s->buffer + i, len - i);
>  
>  	/*
>  	 * Check that nothing has got added in the meantime and truncate