Date: Tue, 10 Oct 2017 00:09:35 -0700 From: Joe Perches <joe@...ches.com> To: "Tobin C. Harding" <me@...in.cc>, kernel-hardening@...ts.openwall.com Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH] lib/vsprintf: add default case to 'i' specifier On Mon, 2017-10-09 at 13:59 +1100, Tobin C. Harding wrote: > %pi leaks kernel addresses if incorrectly specified. Are there any uses that are incorrectly specified? grep doesn't show any. > Currently the printk specifier %pi (%pI) contains a switch statement > without a default clause. The %pi specifier requires a subsequent > character (4, 6, or S) controlling the output. If the specifier is > incomplete the switch statement will fall through and print the variable > argument address in hex instead of the value of the argument (as an IP > address). > > If uncaught this leaks kernel addresses into dmesg. We can return an > error string to make the bug visible and stop addresses leaking. > > Add a default clause returning an error string, stops leaking addresses > and makes the buggy code  > diff --git a/lib/vsprintf.c b/lib/vsprintf.c  > @@ -1775,6 +1775,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, > default: > return string(buf, end, "(invalid address)", spec); > }} > + default: > + return string(buf, end, "(invalid specifier, form: %pi4)", spec); > } > break; > case 'E': I'm not sure this is a big deal and maybe a better way to handle it is to move the %pK, case 'K': block and add a fallthrough or keep the case 'K': block where it is and add a goto.
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