On Tue, Sep 10, 2013 at 10:00 PM, Joe Perches <joe@xxxxxxxxxxx> wrote:
> On Tue, 2013-09-10 at 21:41 -0700, Kees Cook wrote:
>> Make sure that format strings cannot leak into printk() calls from the
>> msgbuf string.
>
> printf(string);
> vs
> printf("%s", string);
>
> How does this help?
In the former case, format characters will get processed by the
sprintf logic. In the latter, they are printed as-is. In this specific
case, if there was a way to inject strings like "ohai %n" into the
msgbuf string, the former would actually attempt to resolve the %n. In
the simple case, this could lead to Oopses, and in the unlucky case,
it could allow arbitrary memory writing and execution control.
http://en.wikipedia.org/wiki/Uncontrolled_format_string
-Kees
--
Kees Cook
Chrome OS Security
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