On Tue, Dec 11, 2012 at 3:04 PM, Eric Dumazet <eric.duma...@gmail.com> wrote:
> On Tue, 2012-12-11 at 14:36 -0800, Ani Sinha wrote:
>> >
>> > It is possible to test for the presence of support of the new vlan bpf
>> > extensions by attempting to load a filter that uses them. As only valid
>> > filters can be loaded, old kernels that do not support filtering of vlan
>> > tags will fail to load the a test filter with uses them.
>>
>> Unfortunately I do not see this. The sk_chk_filter() does not have a
>> default in the case statement and the check will not detect an unknown
>> instruction. It will fail when the filter is run and as far as I can see,
>> the packet will be dropped. Something like this might help?
>>
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index c23543c..96338aa 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -548,6 +548,8 @@ int sk_chk_filter(struct sock_filter *filter, unsigned
>> int flen)
>> return -EINVAL;
>> /* Some instructions need special checks */
>> switch (code) {
>> + /* for unknown instruction, return EINVAL */
>> + default : return -EINVAL;
>> case BPF_S_ALU_DIV_K:
>> /* check for division by zero */
>> if (ftest->k == 0)
>
> This patch is wrong.
yes I generated this patch wrong.
>
> Check lines 546, 547, 548 where we do the check for unknown instructions
>
> code = codes[code];
> if (!code)
> return -EINVAL;
yepph it's OK here.
>
> If you want to test ANCILLARY possible values, its already too late, as
> old kernels wont use any patch anyway.
yepph, I was looking at possible ancilliary values. Basically this
case statement :
#define ANCILLARY(CODE) case SKF_AD_OFF + SKF_AD_##CODE: \
code = BPF_S_ANC_##CODE; \
break
switch (ftest->k) {
ANCILLARY(PROTOCOL);
ANCILLARY(PKTTYPE);
ANCILLARY(IFINDEX);
ANCILLARY(NLATTR);
ANCILLARY(NLATTR_NEST);
ANCILLARY(MARK);
ANCILLARY(QUEUE);
ANCILLARY(HATYPE);
ANCILLARY(RXHASH);
ANCILLARY(CPU);
ANCILLARY(ALU_XOR_X);
ANCILLARY(VLAN_TAG);
ANCILLARY(VLAN_TAG_PRESENT);
}
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