pf: Deal with runt packets

On Ethernet packets have a minimal length, so very short packets get padding
appended to them. This padding is not stripped off in ip6_input() (due to
support for IPv6 Jumbograms, RFC2675).
That means PF needs to be careful when reassembling fragmented packets to not
include the padding in the reassembled packet.

While here also remove the 'Magic from ip_input.' bits. Splitting up and
re-joining an mbuf chain here doesn't make any sense.

Differential Revision:	https://reviews.freebsd.org/D2189
Approved by:		gnn (mentor)

1 files changed, 4 insertions, 4 deletions

diff --git a/sys/netpfil/pf/pf_norm.c b/sys/netpfil/pf/pf_norm.c
index 8aaca93..01c0958 100644
--- a/sys/netpfil/pf/pf_norm.c
+++ b/sys/netpfil/pf/pf_norm.c
@@ -573,11 +573,8 @@ pf_join_fragment(struct pf_fragment *frag)
 	frent = TAILQ_FIRST(&frag->fr_queue);
 	next = TAILQ_NEXT(frent, fr_next);
 
-	/* Magic from ip_input. */
 	m = frent->fe_m;
-	m2 = m->m_next;
-	m->m_next = NULL;
-	m_cat(m, m2);
+	m_adj(m, (frent->fe_hdrlen + frent->fe_len) - m->m_pkthdr.len);
 	uma_zfree(V_pf_frent_z, frent);
 	for (frent = next; frent != NULL; frent = next) {
 		next = TAILQ_NEXT(frent, fr_next);
@@ -585,6 +582,9 @@ pf_join_fragment(struct pf_fragment *frag)
 		m2 = frent->fe_m;
 		/* Strip off ip header. */
 		m_adj(m2, frent->fe_hdrlen);
+		/* Strip off any trailing bytes. */
+		m_adj(m2, frent->fe_len - m2->m_pkthdr.len);
+
 		uma_zfree(V_pf_frent_z, frent);
 		m_cat(m, m2);
 	}