tun + bpf = busted

Tim Robbins tjr at freebsd.org
Tue Nov 11 01:27:13 PST 2003

With INVARIANTS enabled, I get a kernel panic when I run tcpdump on a
"tun" interface. The message is "tunoutput: attempted use of a free mbuf!".
This occurs because tun creates temporary mbufs on the stack and does
not initialize m_flags, so it may or may not have the M_FREELIST bit set
depending on what junk is on the stack. This seems to affect a whole
bunch of other network drivers too.


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