Re: vlan tagged packets and libpcap breakage

[Ani Sinha <ani () aristanetworks com>]

> 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)
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