Re: [tcpdump-workers] vlan tagged packets and libpcap breakage
flat view
From: Ani Sinha <hidden>
Date: 2012-12-11 22:36:45
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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)