network - Assert that the packet's data has not overrrun the buffer in m_free()

* Add an assertion to try to catch subsystems which blow up a mbuf's
  data buffer.

diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index 75120a2..b0bb3f1 100644 (file)
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -922,6 +922,7 @@ m_free(struct mbuf *m)
        struct globaldata *gd = mycpu;
 
        KASSERT(m->m_type != MT_FREE, ("freeing free mbuf %p", m));
+       KASSERT(M_TRAILINGSPACE(m) >= 0, ("overflowed mbuf %p", m));
        atomic_subtract_long_nonlocked(&mbtypes[gd->gd_cpuid][m->m_type], 1);
 
        n = m->m_next;