On Mon, Jun 28, 2010 at 07:48:38PM +0200, Stefani Seibold wrote: > 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. I think sanitizing inputs is more effective than sanitizing outputs. If ->comm is safe internally, then we don't have to filter it going out on printk, audit, /proc output, etc. There is a limited number of places where a process has control over an arbitrary string in kernel structures, so the places where they are set should be fixed instead of fixing every possible usage of it on output. I wouldn't mind sanitizing printk also, but it's tangential to sanitizing task->comm when it is set. -Kees -- Kees Cook Ubuntu Security Team -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
