Messages in this thread | | | Date | Sat, 2 Jul 2011 12:10:22 +0400 | From | Vasiliy Kulikov <> | Subject | Re: [PATCH v2] kernel: escape non-ASCII and control characters in printk() |
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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
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