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Date: Sun, 12 Jun 2011 17:15:45 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: kernel-hardening@...ts.openwall.com
Cc: Willy Tarreau <w@....eu>
Subject: Re: printk()s of user-supplied strings
Solar,
On Sun, Jun 12, 2011 at 06:31 +0400, Solar Designer wrote:
> You could want to review this thread:
>
> http://lists.openwall.net/linux-kernel/2006/08/22/29
>
> (click "thread-next" for further messages).
>
> I don't know (or don't recall) what the outcome of it was, if any.
I don't see any log spoofing protection in the current code.
As a primary threat is \n and \n<X> spoofing, I think the more simple
and bloodless solution would be escaping \n by some string like ">>". So,
the initial
printk(PR_ERR, "Suspicious string: %s\n",
"something\n<1>[ 2533.035243] TCP: possible syn-flood from google.com")
- would result in -
[ 2533.111111] Suspicious string: something
>> <1>[ 2533.035243] TCP: possible syn-flood from google.com
Also all non-printable characters should be escaped on their own (1-31,
possibly, 127-255). \xYYY or similar?
This parsing should be done in "%s" substitution only and in printk()
substitutions only (there are many other users of vscnprintf() and
similar).
An escaping has one drawback - escaped \n looses information about the
log severity. So, this prefixed ">> .." string will be printed as it
would has emergency log severities. It is better than simple log
spoofing, though.
Fully filter "\n" is not a solution as, IIRC, there are legitimate users
of such a multiline feature in the kernel.
Thanks,
--
Vasiliy
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