From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Sender: Vasiliy Kulikov Date: Sat, 2 Jul 2011 12:10:22 +0400 From: Vasiliy Kulikov Message-ID: <20110702081022.GA2755@albatros> References: <20110626190622.GB4217@albatros> <20110626194618.GA21740@elte.hu> <20110626202518.GA4915@albatros> <20110626220126.GA24004@elte.hu> <20110627083633.GA5846@albatros> <20110627104058.45e93c41@pyx> <20110627183829.GA16033@albatros> <20110701143757.GA22567@albatros> <20110701154947.133c30f5@lxorguk.ukuu.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110701154947.133c30f5@lxorguk.ukuu.org.uk> Subject: [kernel-hardening] Re: [PATCH v2] kernel: escape non-ASCII and control characters in printk() To: Alan Cox , Greg Kroah-Hartman Cc: Linus Torvalds , Ingo Molnar , Andrew Morton , James Morris , Namhyung Kim , kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org List-ID: On Fri, Jul 01, 2011 at 15:49 +0100, Alan Cox wrote: > > of the multiline feature. Intoducing new "%S" format for single lines > > makes little sense as there are tons of printk() calls that should be > > already restricted to one line. > > You don't need a new format string surely. Your expectation for printk is > > "multiple new lines are cool providing they are in the format string" > > So that bit isn't hard to deal with, > > You make vprintk take an extra arg (trusted/untrusted args) Not vprintk, but vscnprintf(), vsnprintf() and string() because vprintk() is used in tens of places besides of printk(). Or better implement _vscnprintf(.., bool untrusted) and vscnprintf(...) { return _vscnprintf(..., false); } to leave current users of it as is. But yes, I got the idea. > You make printk pass 'untrusted' > You make %s quote the arguments for control codes What to do with CSI? It is a valid byte inside of a UTF-8 string. Parsing a supplied string assuming it is UTF-8 string and filtering CSI iff it is not a part of UTF-8 symbol is something a bit ugly IMO. Greg - do you know any devices supplying multibyte strings, but not in UTF-8 encoding? If yes, then CSI filtering is a bad idea :\ > At which point your attacker has more work to do but given a long string > yawns and stars using the right number of spaces for the likely 80 col > screen :) Yeah, but introducing some artificial limit for string length is IMO more harmfull: there is no universal limit for all situations, somewhere the resulting string is already 70 chars and even 20 bytes would overflow the col; in rare cases a string of 50 bytes might be still acceptable. Thanks, -- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments