[kernel-hardening] Re: [PATCH] kernel: escape non-ASCII and control characters in printk()

Vasiliy Kulikov
2011-06-22T16:53:55Z

On Wed, Jun 22, 2011 at 09:38 -0700, Joe Perches wrote:
> On Wed, 2011-06-22 at 13:53 +0400, Vasiliy Kulikov wrote:
> > This patch escapes all characters outside of allowed '\n' plus 0x20-0x7E
> > charset passed to printk().
>
> []
>
> > diff --git a/kernel/printk.c b/kernel/printk.c
> []
> > +static void emit_log_char_escaped(char c)
> > +{
> > + char buffer[8];
> > + int i, len;
> > +
> > + if ((c >= ' ' && c < 127) || c == '\n')
>
> if (isprint(c))

#define isprint(c) ((__ismask(c)&(_P|_U|_L|_D|_SP)) != 0)

It slightly differs from what I've written. It (1) lacks '\n', (2)
passes non-ASCII symbols. How would non-ASCII symbols look like if
terminal doesn't support it? (I don't know, merely asking).

But if >159 (the number got from _ctype[]) is not an issue then
(isprint(c) || (c == '\n')) looks really better.

> Why not add this to emit_log_char?

No real need, but someone may want to explicitly bypass the check, it
should use emit_log_char() instead of emit_log_char_escaped().

Thanks,

--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments