Re: [PATCH][RESEND] mm: Fix off-by-one bug in print_nodes_state

[KOSAKI Motohiro]

(12/18/11 5:44 PM), David Rientjes wrote:
> On Sun, 18 Dec 2011, Ryota Ozaki wrote:
>
> > /sys/devices/system/node/{online,possible} involve a garbage byte
> > because print_nodes_state returns content size + 1. To fix the bug,
> > the patch changes the use of cpuset_sprintf_cpulist to follow the
> > use at other places, which is clearer and safer.
>
> It's not a garbage byte, sysdev files use a buffer created with
> get_zeroed_page(), so extra byte is guaranteed to be zero since
> nodelist_scnprintf() won't write to it.  So the issue here is that
> print_nodes_state() returns a size that is off by one according to
> ISO C99 although it won't cause a problem in practice.
>
> > This bug was introduced since v2.6.24.
>
> It's not a bug, the result of a 4-node system would be "0-3\n\0" and
> returns 5 correctly.  You can verify this very simply with strace.

Usually, /sys files don't output trailing '¥0'. And, '¥0' is not regular
io friendly. So I can imagine some careless programmer think it is 
garbage. Is there any benefit to show trailing '¥0'?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/