Date: Tue, 10 Oct 2017 08:27:19 +1100 From: "Tobin C. Harding" <me@...in.cc> To: Tycho Andersen <tycho@...ker.com> Cc: kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH] lib/vsprintf: add default case to 'i' specifier On Mon, Oct 09, 2017 at 09:16:09AM -0600, Tycho Andersen wrote: > On Mon, Oct 09, 2017 at 01:59:05PM +1100, Tobin C. Harding wrote: > > %pi leaks kernel addresses if incorrectly specified. > > > > 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 > > ...? :) > > > Signed-off-by: Tobin C. Harding <me@...in.cc> > > --- > > lib/vsprintf.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > > index 86c3385b9eb3..155702f05b14 100644 > > --- 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: > > Maybe a WARN(1, "invalid pointer format")? That way it'll be easy for > people to figure out where to fix. Thanks for the review. vsprintf.c uses custom error return logic so as not to create a function call cycle, I assume the printf versions of WARN call into vsprintf to do their formatting also. Hence (and without studying the WARN code) I avoided the printf versions of WARN. Open to correction if I am wrong. thanks, Tobin.
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