linux-kernel - Re: [PATCH 1/2] audit: fix NUL handling in untrusted strings

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Date:	Thu, 11 Sep 2008 16:43:19 +0200
From:	Miloslav Trmač <mitr@...hat.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	viro@...iv.linux.org.uk, linux-audit <linux-audit@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] audit: fix NUL handling in untrusted strings

Thanks for the review.
Eric Paris píše v Čt 11. 09. 2008 v 10:25 -0400:
> On Thu, 2008-09-11 at 00:23 +0200, Miloslav Trmač wrote:
> > This patch modifies audit_log_n_untrustedstring() to only log the data
> > before the first NUL byte, if any.
> 
> I'm going to have to say NAK on this patch.
> 
> It's still not right looking at the other user,
> audit_log_single_execve_arg().  An execve arg with a NULL could loose
> the stuff after the NULL (not break the record like audit_tty) since the
> execve uses %s rather than calling trusted string.
execve() arguments are NUL-terminated strings:
audit_log_single_execve_arg() starts with
	len_left = len = strnlen_user(p, MAX_ARG_STRLEN) - 1;
and the two cycles handle chunks in the first "len" bytes of "p".
audit_log_single_execve_arg() never touches any bytes after the first
NUL.

So, when audit_log_single_execve_arg() calls
audit_string_contains_control(buf, to_send), strlen(buf) == to_send and
the patch does not change anything.

> How about we change the meaning of audit_string_contains_control()
> return values?  If it returns positive that is the number of bytes in a
> legitimate string up to the first null.  -1 means it is hex.
That is possible, although the return value convention is somewhat
complex.  Anyway, no change to the semantics of
audit_string_contains_control() is necessary for execve() argument
logging.
	Mirek

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