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authorkp <>2017-04-20 09:05:53 +0000
committerRenato Botelho <>2017-04-20 09:30:28 -0300
commit539d8571ccbd8999cc55736a3adb1c412cd21a5b (patch)
parent26e03fe8d578308454f0b67ed90452003ceb1e31 (diff)
pf: Fix possible incorrect IPv6 fragmentationRELENG_2_3_3
When forwarding pf tracks the size of the largest fragment in a fragmented packet, and refragments based on this size. It failed to ensure that this size was a multiple of 8 (as is required for all but the last fragment), so it could end up generating incorrect fragments. For example, if we received an 8 byte and 12 byte fragment pf would emit a first fragment with 12 bytes of payload and the final fragment would claim to be at offset 8 (not 12). We now assert that the fragment size is a multiple of 8 in ip6_fragment(), so other users won't make the same mistake. Reported by: Antonios Atlasis <aatlasis at secfu net> MFC after: 3 days (cherry picked from commit 4f3397263b95a45dd58e2be3a566029f8841cace)
2 files changed, 6 insertions, 0 deletions
diff --git a/sys/netinet6/ip6_output.c b/sys/netinet6/ip6_output.c
index 09eab20..7af04b0 100644
--- a/sys/netinet6/ip6_output.c
+++ b/sys/netinet6/ip6_output.c
@@ -219,6 +219,8 @@ ip6_fragment(struct ifnet *ifp, struct mbuf *m0, int hlen, u_char nextproto,
int error;
int tlen = m0->m_pkthdr.len;
+ KASSERT(( mtu % 8 == 0), ("Fragment length must be a multiple of 8"));
m = m0;
ip6 = mtod(m, struct ip6_hdr *);
mnext = &m->m_nextpkt;
diff --git a/sys/netpfil/pf/pf_norm.c b/sys/netpfil/pf/pf_norm.c
index 3559909..ead119f 100644
--- a/sys/netpfil/pf/pf_norm.c
+++ b/sys/netpfil/pf/pf_norm.c
@@ -1128,6 +1128,10 @@ pf_refragment6(struct ifnet *ifp, struct mbuf **m0, struct m_tag *mtag)
hdr->ip6_nxt = IPPROTO_FRAGMENT;
+ /* The MTU must be a multiple of 8 bytes, or we risk doing the
+ * fragmentation wrong. */
+ maxlen = maxlen & ~7;
* Maxlen may be less than 8 if there was only a single
* fragment. As it was fragmented before, add a fragment
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