[libvirt] [PATCH] nwfilter: Fix sscanf off-by-one error in virNWFilterSnoopLeaseFileLoad

[Erik Skultety]

On 06/02/2015 11:35 AM, Martin Kletzander wrote:
> On Tue, Jun 02, 2015 at 10:18:34AM +0200, Erik Skultety wrote:
>> We allocate 16 bytes for IPv4 address and 55 bytes for interface
>> key, therefore we should read up to 15/54 bytes and let the last byte
>> reserved for terminating null byte in sscanf.
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=1226400
>> ---
>> src/nwfilter/nwfilter_dhcpsnoop.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/nwfilter/nwfilter_dhcpsnoop.c
>> b/src/nwfilter/nwfilter_dhcpsnoop.c
>> index 6da8983..f331e22 100644
>> --- a/src/nwfilter/nwfilter_dhcpsnoop.c
>> +++ b/src/nwfilter/nwfilter_dhcpsnoop.c
>> @@ -1958,8 +1958,8 @@ virNWFilterSnoopLeaseFileLoad(void)
>>             break;
>>         }
>>         ln++;
>> -        /* key len 55 = "VMUUID"+'-'+"MAC" */
>> -        if (sscanf(line, "%u %55s %16s %16s", &ipl.timeout,
>> +        /* key len 54 = "VMUUID"+'-'+"MAC" */
>> +        if (sscanf(line, "%u %54s %15s %15s", &ipl.timeout,
>>                    ifkey, ipstr, srvstr) < 4) {
> 
> We initialize ifkey as char ifkey[VIR_IFKEY_LEN], so it might be nicer
> to call:
> 
>  if (sscanf(line, "%u %*s %*s %*s", &ipl.timeout,
>                    VIR_IFKEY_LEN - 1, ifkey,
>             INET_ADDRSTRLEN - 1, ipstr,
>             INET_ADDRSTRLEN - 1, srvstr) < 4) {
>      ...
> 
I'd like to disagree --> 'error: too many arguments for format', perhaps
you've mistaken this for printf where man says:
"Instead of a decimal digit string one may write "*" or  "*m$" (for some
decimal integer m) to specify that the field width is given in the next
argument, or in the m-th argument, respectively, which must be of type int."

This however is different for scanf, where '*' is defined as
assignment-suppression character

> But what you have is enough, so ACK to that.
Thanks for the ACK though.

Regards,
Erik