Re: [tcpdump-workers] vlan tagged packets and libpcap breakage
flat view
From: Stephen Hemminger <hidden>
Date: 2012-12-11 23:18:01
On Tue, 11 Dec 2012 14:36:33 -0800 (PST) Ani Sinha [off-list ref] wrote:
quoted hunk ↗ jump to hunk
quoted
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)
Did you test this? I think it will blow up for some existing instructions like BPF_S_ALU_XOR_X or any of the other non-special instructions. Also it is not formatted correctly for the kernel programming style. ERROR: space prohibited before that ':' (ctx:WxW) #86: FILE: net/core/filter.c:552: + default : return -EINVAL; ^