Re: [dpdk-dev] [PATCH v2] examples/vm_power_manager: fix string null termination

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Apr 26, 2019 at 12:56:08PM +0100, Burakov, Anatoly wrote:
> On 26-Apr-19 12:24 PM, David Hunt wrote:
> > coverity complains about a null-termination after a read,
> > so we terminate after exiting the do-while loop. The position
> > is conditional on whether idx is within the buffer or at the
> > end of the buffer.
> > 
> > Coverity issue: 337680
> > Fixes: a63504a90f ("examples/power: add JSON string handling")
> > CC: stable@dpdk.org
> > 
> > Signed-off-by: David Hunt <david.hunt@intel.com>
> > 
> > ---
> > v2:
> >     * Move null termination outside of do-while.
> > ---
> >   examples/vm_power_manager/channel_monitor.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/examples/vm_power_manager/channel_monitor.c b/examples/vm_power_manager/channel_monitor.c
> > index 971e4f2bc..03fdcd15a 100644
> > --- a/examples/vm_power_manager/channel_monitor.c
> > +++ b/examples/vm_power_manager/channel_monitor.c
> > @@ -822,6 +822,8 @@ read_json_packet(struct channel_info *chan_info)
> >   				break;
> >   		} while (indent > 0);
> > +		json_data[idx + (idx < MAX_JSON_STRING_LEN - 1)] = '\0';
> > +
> 
> I don't think you need this complicated logic here. You start at idx = 0, so
> even if you receive 0 bytes, you'll terminate buffer at index 0. You also
> break when idx reaches (MAX_JSON_STRING_LEN - 1), so it's also safe to do
> json_data[idx] after the loop. In all other cases, you still increment idx
> before breaking out (e.g. when reaching indent == 0), so it's also safe to
> do json_data[idx] in those cases.
> 
+1 to that.

An alternative and simpler option might be to memset the who array to zero
before you start anyway.

/Bruce