[ovs-discuss] [ovn] non-maskable OVS meta-flow fields not correctly handled

ythomas1.ext at orange.com ythomas1.ext at orange.com
Thu Nov 5 12:39:38 UTC 2020


I’m currently working on OVN to add MPLS logical fields (such as 'mpls_label', 'mpls_bos') to support BGP/MPLS technology.

As indicated in 'mf_field' struct in meta-flow.h, most OVS meta-flow fields have n_bytes * 8 == n_bits size but there are few exceptions such as 'mpls_label', 'mpls_bos', etc…

In OVN case, when calling 'mf_mask_subfield' method from meta-flow.c, for example for 'mpls_label' OVS meta-flow field which has 20 useful bits over 32 bits, the 'mask' value parsed in OVN is set to 0xffff00ff (which seems correct).

The problem is that in 'mf_set' method, 'mpls_label' OVS meta-flow field is supposed to only have a NULL, all-1-bits or all-0-bits 'mask' value to be set, as shown below:

mf_set(const struct mf_field *mf,
       const union mf_value *value, const union mf_value *mask,
       struct match *match, char **err_str)
    if (!mask || is_all_ones(mask, mf->n_bytes)) {
        mf_set_value(mf, value, match, err_str);
        return mf->usable_protocols_exact;
    } else if (is_all_zeros(mask, mf->n_bytes) && !mf_is_tun_metadata(mf)) {
        /* Tunnel metadata matches on the existence of the field itself, so
         * it still needs to be encoded even if the value is wildcarded. */
        mf_set_wild(mf, match, err_str);
        return OFPUTIL_P_ANY;
    } …
    switch (mf->id) {
    case MFF_MPLS_LABEL:
    case MFF_MPLS_TC:
    case MFF_MPLS_BOS:
    case MFF_MPLS_TTL:
        return OFPUTIL_P_NONE;

However, as mentioned in 'mf_set' method comment, “The caller is responsible for ensuring that 'match' meets 'mf''s prerequisites”.

So, since the 'mpls_label' OVS meta-flow field is indicated as not maskable in meta-flow.h, shouldn't OVN ensure that 'mask' is set to NULL when calling 'mf_mask_subfield'  ?

Best regards,

Yannick Thomas


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