4.4-stable review patch. If anyone has any objections, please let me know.
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From: Peter Oskolkov posk@google.com
commit 7969e5c40dfd04799d4341f1b7cd266b6e47f227 upstream.
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 Signed-off-by: Mao Wenan maowenan@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/uapi/linux/snmp.h | 1 net/ipv4/ip_fragment.c | 73 ++++++++++++---------------------------------- net/ipv4/proc.c | 1 3 files changed, 22 insertions(+), 53 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 @@ -342,6 +342,7 @@ 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; @@ -422,60 +423,22 @@ 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 = (FRAG_CB(prev)->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 && FRAG_CB(next)->offset < end) { - int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */ - - if (i < next->len) { - /* Eat head of the next overlapped fragment - * and leave the loop. The next ones cannot overlap. - */ - if (!pskb_pull(next, i)) - goto err; - FRAG_CB(next)->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 && + (FRAG_CB(prev)->offset + prev->len) > offset) + goto discard_qp; + + /* Is there an overlap with the next fragment? */ + if (next && FRAG_CB(next)->offset < end) + goto discard_qp;
FRAG_CB(skb)->offset = offset;
@@ -522,6 +485,10 @@ found: skb_dst_drop(skb); return -EINPROGRESS;
+discard_qp: + ipq_kill(qp); + 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 @@ -132,6 +132,7 @@ 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 };