Re: [PATCH v2] sanitize task->comm to avoid leaking escape codes
From: KOSAKI Motohiro
Date: Mon Jun 28 2010 - 23:06:23 EST
> Am Freitag, den 25.06.2010, 08:56 +0900 schrieb KOSAKI Motohiro:
> > > Through get_task_comm() and many direct uses of task->comm in the kernel,
> > > it is possible for escape codes and other non-printables to leak into
> > > dmesg, syslog, etc. In the worst case, these strings could be used to
> > > attack administrators using vulnerable terminal emulators, and at least
> > > cause confusion through the injection of \r characters.
> > >
> > > This patch sanitizes task->comm to only contain printable characters
> > > when it is set. Additionally, it redefines get_task_comm so that it is
> > > more obvious when misused by callers (presently nothing was incorrectly
> > > calling get_task_comm's unsafe use of strncpy).
> > >
> > > Signed-off-by: Kees Cook <kees.cook@xxxxxxxxxxxxx>
> > I've reviewed this patch briefly, Here is my personal concern...
> > On Linux, non-printable leaking is fundamental, only fixing task->comm
> > doesn't solve syslog exploit issue. Probably all /proc/kmsg user should
> > have escaping non-pritables code.
> > However, task->comm is one of most easy injection data of kernel, because
> > we have prctl(PR_SET_NAME), attacker don't need root privilege. So,
> > conservative assumption seems guard from crappy fault. Plus, this patch
> > is very small and our small TASK_COMM_LEN lead that we don't need
> > big performance concern.
> > So, I don't find demerit in this proposal. but I'm not security specialist,
> > it's only personal thinking.
> Agree. I think a escaped printk should be a more generic solution.
Is this possible? printk() doesn't know userland locale. how do it escape correctly?
When we only concern task->comm, assuming ascii-only string is enough practical.
but printk generic logic should allow non-ascii, I think.
I think userland reader process only know correct escaping way.
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