From mboxrd@z Thu Jan  1 00:00:00 1970
From: joe@perches.com (Joe Perches)
Date: Tue, 05 Jun 2012 17:37:24 -0700
Subject: [PATCH 0/8] Rework KERN_<LEVEL>
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Message-ID: <1338943044.11962.26.camel@joe2Laptop>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, 2012-06-06 at 02:28 +0200, Kay Sievers wrote:
> On Wed, Jun 6, 2012 at 2:19 AM, Joe Perches <joe@perches.com> wrote:
> > On Wed, 2012-06-06 at 02:13 +0200, Kay Sievers wrote:
> >> The question is what happens if you inject your new binary two-byte
> >> prefix, like:
> >>   echo -e "\x01\x02Hello" > /dev/kmsg
> >
> > It's not a 2 byte binary.
> > It's a leading ascii SOH and a standard ascii char
> > '0' ... '7' or 'd'.
> >
> > #define KERN_EMERG      KERN_SOH "0"    /* system is unusable */
> > #define KERN_ALERT      KERN_SOH "1"    /* action must be taken immediately */
> > etc...
> 
> Ok.
> 
> >> And if that changes the log-level to "2" instead of the default "4"?
> >
> > No it doesn't.
> 
> So:
>    echo -e "\x012Hello" > /dev/kmsg
> is still level 4? Sounds all fine then.

Yes.
# echo -e "\x012Hello again Kay" > /dev/kmsg
gives:
12,780,6031964979;Hello again Kay

> > It's not triggering that because devkmsg_writev does
> > prefix parsing only on the old "<n>" form.
> 
> Yeah, but printk_emit() will not try to parse it? I did not check, but
> with your change, the prefix parsing in printk_emit() is still skipped
> if a level is given as a parameter to printk_emit(), right?

If level is not -1, then whatever prefix level the
string has is ignored by vprintk_emit.

from vprintk_emit:

	/* strip syslog prefix and extract log level or control flags */
	kern_level = printk_get_level(text);
	if (kern_level) {
		const char *end_of_header = printk_skip_level(text);
		switch (kern_level) {
		case '0' ... '7':
			if (level == -1)
				level = kern_level - '0';
		case 'd': /* Strip d KERN_DEFAULT, start new line */
			plen = 0;
		default:
			if (!new_text_line) {
				log_buf_emit_char('\n');
				new_text_line = 1;
			}
		}
		text_len -=  end_of_header - text;
		text = (char *)end_of_header;
	}

Only level == -1 will use the prefix level.

devkmsg_writev always passes a non -1 level.

cheers, Joe