From 5d5b5d0f99378377cadb99b62d9a1b5d9f7ecd81 Mon Sep 17 00:00:00 2001
From: Mike Silbersack <silby@FreeBSD.org>
Date: Sun, 19 Oct 2003 22:33:41 +0000
Subject: [PATCH] Add a new macro M_ASSERTVALID which ensures that the mbuf in
 question is non-free.  (More checks can/should be added in the future.)

Use M_ASSERTVALID in BPF_MTAP so that we catch when freed mbufs are
passed in, even if no bpf listeners are active.

Inspired by a bug in if_dc caught by Kenjiro Cho.
---
 sys/net/bpf.h  | 1 +
 sys/sys/mbuf.h | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/sys/net/bpf.h b/sys/net/bpf.h
index 6d3e80096e00..a5942ae21939 100644
--- a/sys/net/bpf.h
+++ b/sys/net/bpf.h
@@ -366,6 +366,7 @@ u_int	 bpf_filter(const struct bpf_insn *, u_char *, u_int, u_int);
 		bpf_tap((_ifp)->if_bpf, (_pkt), (_pktlen));	\
 } while (0)
 #define	BPF_MTAP(_ifp,_m) do {					\
+	M_ASSERTVALID(_m);					\
 	if ((_ifp)->if_bpf)					\
 		bpf_mtap((_ifp)->if_bpf, (_m));			\
 } while (0)
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index abdd6625f06b..6fa1ef7bf9ed 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -339,6 +339,13 @@ struct mbstat {
 	KASSERT(m != NULL && m->m_flags & M_PKTHDR,	\
 		("%s: no mbuf packet header!", __func__))
 
+/*
+ * Ensure that the supplied mbuf is a valid, non-free mbuf.
+ */
+#define M_ASSERTVALID(m)					\
+	KASSERT((((struct mbuf *)m)->m_flags & M_FREELIST) == 0,			\
+		("%s: attempted use of a free mbuf!", __func__))
+
 /*
  * Set the m_data pointer of a newly-allocated mbuf (m_get/MGET) to place
  * an object of the specified size at the end of the mbuf, longword aligned.