Re: [Qemu-devel] [PATCH] qdev: Validate hex properties

[Eric Blake]

On 11/26/2013 08:05 AM, Hannes Reinecke wrote:
> strtoull() might return '-1' to signify an overflow.

Yes, but -1 (aka ULLONG_MAX) is also a valid return when there is not
overflow, so testing for -1 is NOT a reliable indicator on whether
overflow occurred.  Also, you mention strtoull() here...

> 
> Signed-off-by: Hannes Reinecke <address@hidden>
> ---
>  hw/core/qdev-properties.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
> index dc8ae69..5761295 100644
> --- a/hw/core/qdev-properties.c
> +++ b/hw/core/qdev-properties.c
> @@ -202,6 +202,9 @@ static int parse_hex8(DeviceState *dev, Property *prop, 
> const char *str)
>      if ((*end != '\0') || (end == str)) {

...but this was calling strtoul().

>          return -EINVAL;
>      }
> +    if (*ptr == (uint8_t)-1) {
> +        return -ERANGE;
> +    }

NAK.  This is NOT how you check for overflow with strtoull.  Instead,
you should use:

errno = 0;
*ptr = strtoul(str, &end, 16);
if (errno) {
    return -errno;
}
if (!*end || end == str) {
    return -EINVAL;
}
return 0;

>  
>      return 0;
>  }
> @@ -333,6 +336,9 @@ static int parse_hex32(DeviceState *dev, Property *prop, 
> const char *str)
>      if ((*end != '\0') || (end == str)) {
>          return -EINVAL;
>      }
> +    if (*ptr == (uint32_t)-1) {
> +        return -ERANGE;
> +    }

NAK.  And this function is even MORE broken.  On a 32-bit platform,
assigning the results of strtol() into a uint32_t may result in silent
truncation.  If you are trying to detect overflow, you MUST assign the
results into a long, then check that the long does not overflow
uint32_t, rather than checking (too late) whether the uint32_t has
already been overflowed.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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