4.9-stable review patch. If anyone has any objections, please let me know.
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From: Peter Oskolkov posk@google.com
This behavior is required in IPv6, and there is little need to tolerate overlapping fragments in IPv4. This change simplifies the code and eliminates potential DDoS attack vectors.
Tested: ran ip_defrag selftest (not yet available uptream).
Suggested-by: David S. Miller davem@davemloft.net Signed-off-by: Peter Oskolkov posk@google.com Signed-off-by: Eric Dumazet edumazet@google.com Cc: Florian Westphal fw@strlen.de Acked-by: Stephen Hemminger stephen@networkplumber.org Signed-off-by: David S. Miller davem@davemloft.net (cherry picked from commit 7969e5c40dfd04799d4341f1b7cd266b6e47f227) Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/uapi/linux/snmp.h | 1 net/ipv4/ip_fragment.c | 77 +++++++++++----------------------------------- net/ipv4/proc.c | 1 3 files changed, 22 insertions(+), 57 deletions(-)
--- a/include/uapi/linux/snmp.h +++ b/include/uapi/linux/snmp.h @@ -55,6 +55,7 @@ enum IPSTATS_MIB_ECT1PKTS, /* InECT1Pkts */ IPSTATS_MIB_ECT0PKTS, /* InECT0Pkts */ IPSTATS_MIB_CEPKTS, /* InCEPkts */ + IPSTATS_MIB_REASM_OVERLAPS, /* ReasmOverlaps */ __IPSTATS_MIB_MAX };
--- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c @@ -275,6 +275,7 @@ static int ip_frag_reinit(struct ipq *qp /* Add new segment to existing queue. */ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) { + struct net *net = container_of(qp->q.net, struct net, ipv4.frags); struct sk_buff *prev, *next; struct net_device *dev; unsigned int fragsize; @@ -355,65 +356,23 @@ static int ip_frag_queue(struct ipq *qp, }
found: - /* We found where to put this one. Check for overlap with - * preceding fragment, and, if needed, align things so that - * any overlaps are eliminated. + /* RFC5722, Section 4, amended by Errata ID : 3089 + * When reassembling an IPv6 datagram, if + * one or more its constituent fragments is determined to be an + * overlapping fragment, the entire datagram (and any constituent + * fragments) MUST be silently discarded. + * + * We do the same here for IPv4. */ - if (prev) { - int i = (prev->ip_defrag_offset + prev->len) - offset;
- if (i > 0) { - offset += i; - err = -EINVAL; - if (end <= offset) - goto err; - err = -ENOMEM; - if (!pskb_pull(skb, i)) - goto err; - if (skb->ip_summed != CHECKSUM_UNNECESSARY) - skb->ip_summed = CHECKSUM_NONE; - } - } - - err = -ENOMEM; - - while (next && next->ip_defrag_offset < end) { - int i = end - next->ip_defrag_offset; /* overlap is 'i' bytes */ - - if (i < next->len) { - int delta = -next->truesize; - - /* Eat head of the next overlapped fragment - * and leave the loop. The next ones cannot overlap. - */ - if (!pskb_pull(next, i)) - goto err; - delta += next->truesize; - if (delta) - add_frag_mem_limit(qp->q.net, delta); - next->ip_defrag_offset += i; - qp->q.meat -= i; - if (next->ip_summed != CHECKSUM_UNNECESSARY) - next->ip_summed = CHECKSUM_NONE; - break; - } else { - struct sk_buff *free_it = next; - - /* Old fragment is completely overridden with - * new one drop it. - */ - next = next->next; - - if (prev) - prev->next = next; - else - qp->q.fragments = next; - - qp->q.meat -= free_it->len; - sub_frag_mem_limit(qp->q.net, free_it->truesize); - kfree_skb(free_it); - } - } + /* Is there an overlap with the previous fragment? */ + if (prev && + (prev->ip_defrag_offset + prev->len) > offset) + goto discard_qp; + + /* Is there an overlap with the next fragment? */ + if (next && next->ip_defrag_offset < end) + goto discard_qp;
/* Note : skb->ip_defrag_offset and skb->dev share the same location */ dev = skb->dev; @@ -461,6 +420,10 @@ found: skb_dst_drop(skb); return -EINPROGRESS;
+discard_qp: + inet_frag_kill(&qp->q); + err = -EINVAL; + __IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS); err: kfree_skb(skb); return err; --- a/net/ipv4/proc.c +++ b/net/ipv4/proc.c @@ -134,6 +134,7 @@ static const struct snmp_mib snmp4_ipext SNMP_MIB_ITEM("InECT1Pkts", IPSTATS_MIB_ECT1PKTS), SNMP_MIB_ITEM("InECT0Pkts", IPSTATS_MIB_ECT0PKTS), SNMP_MIB_ITEM("InCEPkts", IPSTATS_MIB_CEPKTS), + SNMP_MIB_ITEM("ReasmOverlaps", IPSTATS_MIB_REASM_OVERLAPS), SNMP_MIB_SENTINEL };