On Wed, Sep 11, 2013 at 2:31 AM, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: > On Tue, Sep 10, 2013 at 10:19:17PM -0700, Kees Cook wrote: >> 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 > > The kernel ignores %n so hopefully it can't actually write to memory. I wish! This is not the case, though. See FORMAT_TYPE_NRCHARS in lib/vsprintf.c's vsnprintf(). $ git grep '%n' | wc -l 111 -Kees -- Kees Cook Chrome OS Security _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
