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SubjectRe: [net-dsa-mv88e6xxx] question about potential use of uninitialized variable
Hi Andrew,

Quoting Andrew Lunn <andrew@lunn.ch>:

> On Thu, May 11, 2017 at 04:35:37PM -0500, Gustavo A. R. Silva wrote:
>>
>> Hello everybody,
>>
>> While looking into Coverity ID 1398130 I ran into the following
>> piece of code at drivers/net/dsa/mv88e6xxx/chip.c:849:
>>
>> 849static uint64_t _mv88e6xxx_get_ethtool_stat(struct mv88e6xxx_chip *chip,
>> 850 struct mv88e6xxx_hw_stat *s,
>> 851 int port, u16 bank1_select,
>> 852 u16 histogram)
>> 853{
>> 854 u32 low;
>> 855 u32 high = 0;
>> 856 u16 reg = 0;
>> 857 int err;
>> 858 u64 value;
>> 859
>> 860 switch (s->type) {
>> 861 case STATS_TYPE_PORT:
>> 862 err = mv88e6xxx_port_read(chip, port, s->reg, &reg);
>> 863 if (err)
>> 864 return UINT64_MAX;
>> 865
>> 866 low = reg;
>> 867 if (s->sizeof_stat == 4) {
>> 868 err = mv88e6xxx_port_read(chip, port,
>> s->reg + 1, &reg);
>> 869 if (err)
>> 870 return UINT64_MAX;
>> 871 high = reg;
>> 872 }
>> 873 break;
>> 874 case STATS_TYPE_BANK1:
>> 875 reg = bank1_select;
>> 876 /* fall through */
>> 877 case STATS_TYPE_BANK0:
>> 878 reg |= s->reg | histogram;
>> 879 mv88e6xxx_g1_stats_read(chip, reg, &low);
>> 880 if (s->sizeof_stat == 8)
>> 881 mv88e6xxx_g1_stats_read(chip, reg + 1, &high);
>> 882 }
>> 883 value = (((u64)high) << 16) | low;
>> 884 return value;
>> 885}
>>
>> My question here is if there is any chance for the execution path to
>> directly jump from line 860 to line 883, hence ending up using the
>> uninitialized variable _low_?
>
> Hi Gustavo
>
> It would require that s->type not have one of the listed case values.
> Currently all members of mv88e6xxx_hw_stats due use expected values.
> However, it would not hurt to add a
>
> default:
> return UINT64_MAX;
>
> Do you want to submit a patch?
>

Sure, I'll send it shortly.

Thanks for clarifying!
--
Gustavo A. R. Silva






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