From 3a1214e8b06317b4e71cd3a36344df87b7858e19 Mon Sep 17 00:00:00 2001 From: Tom Herbert Date: Fri, 1 Sep 2017 14:04:11 -0700 Subject: flow_dissector: Cleanup control flow __skb_flow_dissect is riddled with gotos that make discerning the flow, debugging, and extending the capability difficult. This patch reorganizes things so that we only perform goto's after the two main switch statements (no gotos within the cases now). It also eliminates several goto labels so that there are only two labels that can be target for goto. Reported-by: Alexander Popov Signed-off-by: Tom Herbert Signed-off-by: David S. Miller --- include/net/flow_dissector.h | 8 ++ net/core/flow_dissector.c | 223 ++++++++++++++++++++++++++++--------------- 2 files changed, 153 insertions(+), 78 deletions(-) diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h index e2663e900b0a..fc3dce730a6b 100644 --- a/include/net/flow_dissector.h +++ b/include/net/flow_dissector.h @@ -19,6 +19,14 @@ struct flow_dissector_key_control { #define FLOW_DIS_FIRST_FRAG BIT(1) #define FLOW_DIS_ENCAPSULATION BIT(2) +enum flow_dissect_ret { + FLOW_DISSECT_RET_OUT_GOOD, + FLOW_DISSECT_RET_OUT_BAD, + FLOW_DISSECT_RET_PROTO_AGAIN, + FLOW_DISSECT_RET_IPPROTO_AGAIN, + FLOW_DISSECT_RET_CONTINUE, +}; + /** * struct flow_dissector_key_basic: * @thoff: Transport header offset diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index e2eaa1ff948d..e0ea17d1c7fc 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -115,12 +115,6 @@ __be32 __skb_flow_get_ports(const struct sk_buff *skb, int thoff, u8 ip_proto, } EXPORT_SYMBOL(__skb_flow_get_ports); -enum flow_dissect_ret { - FLOW_DISSECT_RET_OUT_GOOD, - FLOW_DISSECT_RET_OUT_BAD, - FLOW_DISSECT_RET_OUT_PROTO_AGAIN, -}; - static enum flow_dissect_ret __skb_flow_dissect_mpls(const struct sk_buff *skb, struct flow_dissector *flow_dissector, @@ -341,7 +335,7 @@ __skb_flow_dissect_gre(const struct sk_buff *skb, if (flags & FLOW_DISSECTOR_F_STOP_AT_ENCAP) return FLOW_DISSECT_RET_OUT_GOOD; - return FLOW_DISSECT_RET_OUT_PROTO_AGAIN; + return FLOW_DISSECT_RET_PROTO_AGAIN; } static void @@ -431,6 +425,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb, struct flow_dissector_key_icmp *key_icmp; struct flow_dissector_key_tags *key_tags; struct flow_dissector_key_vlan *key_vlan; + enum flow_dissect_ret fdret; bool skip_vlan = false; u8 ip_proto = 0; bool ret; @@ -482,14 +477,19 @@ bool __skb_flow_dissect(const struct sk_buff *skb, } proto_again: + fdret = FLOW_DISSECT_RET_CONTINUE; + switch (proto) { case htons(ETH_P_IP): { const struct iphdr *iph; struct iphdr _iph; -ip: + iph = __skb_header_pointer(skb, nhoff, sizeof(_iph), data, hlen, &_iph); - if (!iph || iph->ihl < 5) - goto out_bad; + if (!iph || iph->ihl < 5) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } + nhoff += iph->ihl * 4; ip_proto = iph->protocol; @@ -509,19 +509,25 @@ ip: key_control->flags |= FLOW_DIS_IS_FRAGMENT; if (iph->frag_off & htons(IP_OFFSET)) { - goto out_good; + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; } else { key_control->flags |= FLOW_DIS_FIRST_FRAG; - if (!(flags & FLOW_DISSECTOR_F_PARSE_1ST_FRAG)) - goto out_good; + if (!(flags & + FLOW_DISSECTOR_F_PARSE_1ST_FRAG)) { + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; + } } } __skb_flow_dissect_ipv4(skb, flow_dissector, target_container, data, iph); - if (flags & FLOW_DISSECTOR_F_STOP_AT_L3) - goto out_good; + if (flags & FLOW_DISSECTOR_F_STOP_AT_L3) { + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; + } break; } @@ -529,10 +535,11 @@ ip: const struct ipv6hdr *iph; struct ipv6hdr _iph; -ipv6: iph = __skb_header_pointer(skb, nhoff, sizeof(_iph), data, hlen, &_iph); - if (!iph) - goto out_bad; + if (!iph) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } ip_proto = iph->nexthdr; nhoff += sizeof(struct ipv6hdr); @@ -561,15 +568,17 @@ ipv6: target_container); key_tags->flow_label = ntohl(flow_label); } - if (flags & FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL) - goto out_good; + if (flags & FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL) { + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; + } } __skb_flow_dissect_ipv6(skb, flow_dissector, target_container, data, iph); if (flags & FLOW_DISSECTOR_F_STOP_AT_L3) - goto out_good; + fdret = FLOW_DISSECT_RET_OUT_GOOD; break; } @@ -585,12 +594,17 @@ ipv6: if (!vlan_tag_present || eth_type_vlan(skb->protocol)) { vlan = __skb_header_pointer(skb, nhoff, sizeof(_vlan), data, hlen, &_vlan); - if (!vlan) - goto out_bad; + if (!vlan) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } + proto = vlan->h_vlan_encapsulated_proto; nhoff += sizeof(*vlan); - if (skip_vlan) - goto proto_again; + if (skip_vlan) { + fdret = FLOW_DISSECT_RET_PROTO_AGAIN; + break; + } } skip_vlan = true; @@ -613,7 +627,8 @@ ipv6: } } - goto proto_again; + fdret = FLOW_DISSECT_RET_PROTO_AGAIN; + break; } case htons(ETH_P_PPP_SES): { struct { @@ -621,18 +636,27 @@ ipv6: __be16 proto; } *hdr, _hdr; hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr); - if (!hdr) - goto out_bad; + if (!hdr) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } + proto = hdr->proto; nhoff += PPPOE_SES_HLEN; switch (proto) { case htons(PPP_IP): - goto ip; + proto = htons(ETH_P_IP); + fdret = FLOW_DISSECT_RET_PROTO_AGAIN; + break; case htons(PPP_IPV6): - goto ipv6; + proto = htons(ETH_P_IPV6); + fdret = FLOW_DISSECT_RET_PROTO_AGAIN; + break; default: - goto out_bad; + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; } + break; } case htons(ETH_P_TIPC): { struct { @@ -640,8 +664,10 @@ ipv6: __be32 srcnode; } *hdr, _hdr; hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr); - if (!hdr) - goto out_bad; + if (!hdr) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } if (dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_TIPC_ADDRS)) { @@ -651,56 +677,62 @@ ipv6: key_addrs->tipcaddrs.srcnode = hdr->srcnode; key_control->addr_type = FLOW_DISSECTOR_KEY_TIPC_ADDRS; } - goto out_good; + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; } case htons(ETH_P_MPLS_UC): case htons(ETH_P_MPLS_MC): -mpls: - switch (__skb_flow_dissect_mpls(skb, flow_dissector, + fdret = __skb_flow_dissect_mpls(skb, flow_dissector, target_container, data, - nhoff, hlen)) { - case FLOW_DISSECT_RET_OUT_GOOD: - goto out_good; - case FLOW_DISSECT_RET_OUT_BAD: - default: - goto out_bad; - } + nhoff, hlen); + break; case htons(ETH_P_FCOE): - if ((hlen - nhoff) < FCOE_HEADER_LEN) - goto out_bad; + if ((hlen - nhoff) < FCOE_HEADER_LEN) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } nhoff += FCOE_HEADER_LEN; - goto out_good; + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; case htons(ETH_P_ARP): case htons(ETH_P_RARP): - switch (__skb_flow_dissect_arp(skb, flow_dissector, + fdret = __skb_flow_dissect_arp(skb, flow_dissector, target_container, data, - nhoff, hlen)) { - case FLOW_DISSECT_RET_OUT_GOOD: - goto out_good; - case FLOW_DISSECT_RET_OUT_BAD: - default: - goto out_bad; - } + nhoff, hlen); + break; + + default: + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } + + /* Process result of proto processing */ + switch (fdret) { + case FLOW_DISSECT_RET_OUT_GOOD: + goto out_good; + case FLOW_DISSECT_RET_PROTO_AGAIN: + goto proto_again; + case FLOW_DISSECT_RET_CONTINUE: + case FLOW_DISSECT_RET_IPPROTO_AGAIN: + break; + case FLOW_DISSECT_RET_OUT_BAD: default: goto out_bad; } ip_proto_again: + fdret = FLOW_DISSECT_RET_CONTINUE; + switch (ip_proto) { case IPPROTO_GRE: - switch (__skb_flow_dissect_gre(skb, key_control, flow_dissector, + fdret = __skb_flow_dissect_gre(skb, key_control, flow_dissector, target_container, data, - &proto, &nhoff, &hlen, flags)) { - case FLOW_DISSECT_RET_OUT_GOOD: - goto out_good; - case FLOW_DISSECT_RET_OUT_BAD: - goto out_bad; - case FLOW_DISSECT_RET_OUT_PROTO_AGAIN: - goto proto_again; - } + &proto, &nhoff, &hlen, flags); + break; + case NEXTHDR_HOP: case NEXTHDR_ROUTING: case NEXTHDR_DEST: { @@ -711,13 +743,16 @@ ip_proto_again: opthdr = __skb_header_pointer(skb, nhoff, sizeof(_opthdr), data, hlen, &_opthdr); - if (!opthdr) - goto out_bad; + if (!opthdr) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } ip_proto = opthdr[0]; nhoff += (opthdr[1] + 1) << 3; - goto ip_proto_again; + fdret = FLOW_DISSECT_RET_IPPROTO_AGAIN; + break; } case NEXTHDR_FRAGMENT: { struct frag_hdr _fh, *fh; @@ -728,8 +763,10 @@ ip_proto_again: fh = __skb_header_pointer(skb, nhoff, sizeof(_fh), data, hlen, &_fh); - if (!fh) - goto out_bad; + if (!fh) { + fdret = FLOW_DISSECT_RET_OUT_BAD; + break; + } key_control->flags |= FLOW_DIS_IS_FRAGMENT; @@ -738,34 +775,50 @@ ip_proto_again: if (!(fh->frag_off & htons(IP6_OFFSET))) { key_control->flags |= FLOW_DIS_FIRST_FRAG; - if (flags & FLOW_DISSECTOR_F_PARSE_1ST_FRAG) - goto ip_proto_again; + if (flags & FLOW_DISSECTOR_F_PARSE_1ST_FRAG) { + fdret = FLOW_DISSECT_RET_IPPROTO_AGAIN; + break; + } } - goto out_good; + + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; } case IPPROTO_IPIP: proto = htons(ETH_P_IP); key_control->flags |= FLOW_DIS_ENCAPSULATION; - if (flags & FLOW_DISSECTOR_F_STOP_AT_ENCAP) - goto out_good; + if (flags & FLOW_DISSECTOR_F_STOP_AT_ENCAP) { + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; + } + + fdret = FLOW_DISSECT_RET_PROTO_AGAIN; + break; - goto ip; case IPPROTO_IPV6: proto = htons(ETH_P_IPV6); key_control->flags |= FLOW_DIS_ENCAPSULATION; - if (flags & FLOW_DISSECTOR_F_STOP_AT_ENCAP) - goto out_good; + if (flags & FLOW_DISSECTOR_F_STOP_AT_ENCAP) { + fdret = FLOW_DISSECT_RET_OUT_GOOD; + break; + } + + fdret = FLOW_DISSECT_RET_PROTO_AGAIN; + break; + - goto ipv6; case IPPROTO_MPLS: proto = htons(ETH_P_MPLS_UC); - goto mpls; + fdret = FLOW_DISSECT_RET_PROTO_AGAIN; + break; + case IPPROTO_TCP: __skb_flow_dissect_tcp(skb, flow_dissector, target_container, data, nhoff, hlen); break; + default: break; } @@ -787,6 +840,20 @@ ip_proto_again: key_icmp->icmp = skb_flow_get_be16(skb, nhoff, data, hlen); } + /* Process result of IP proto processing */ + switch (fdret) { + case FLOW_DISSECT_RET_PROTO_AGAIN: + goto proto_again; + case FLOW_DISSECT_RET_IPPROTO_AGAIN: + goto ip_proto_again; + case FLOW_DISSECT_RET_OUT_GOOD: + case FLOW_DISSECT_RET_CONTINUE: + break; + case FLOW_DISSECT_RET_OUT_BAD: + default: + goto out_bad; + } + out_good: ret = true; -- cgit v1.2.3 From 1eed4dfb81b193af3299edeed2827337f9999e78 Mon Sep 17 00:00:00 2001 From: Tom Herbert Date: Fri, 1 Sep 2017 14:04:12 -0700 Subject: flow_dissector: Add limit for number of headers to dissect In flow dissector there are no limits to the number of nested encapsulations or headers that might be dissected which makes for a nice DOS attack. This patch sets a limit of the number of headers that flow dissector will parse. Headers includes network layer headers, transport layer headers, shim headers for encapsulation, IPv6 extension headers, etc. The limit for maximum number of headers to parse has be set to fifteen to account for a reasonable number of encapsulations, extension headers, VLAN, in a packet. Note that this limit does not supercede the STOP_AT_* flags which may stop processing before the headers limit is reached. Reported-by: Hannes Frederic Sowa Signed-off-by: Tom Herbert Signed-off-by: David S. Miller --- net/core/flow_dissector.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-) diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index e0ea17d1c7fc..0a977373d003 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -396,6 +396,18 @@ __skb_flow_dissect_ipv6(const struct sk_buff *skb, key_ip->ttl = iph->hop_limit; } +/* Maximum number of protocol headers that can be parsed in + * __skb_flow_dissect + */ +#define MAX_FLOW_DISSECT_HDRS 15 + +static bool skb_flow_dissect_allowed(int *num_hdrs) +{ + ++*num_hdrs; + + return (*num_hdrs <= MAX_FLOW_DISSECT_HDRS); +} + /** * __skb_flow_dissect - extract the flow_keys struct and return it * @skb: sk_buff to extract the flow from, can be NULL if the rest are specified @@ -427,6 +439,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb, struct flow_dissector_key_vlan *key_vlan; enum flow_dissect_ret fdret; bool skip_vlan = false; + int num_hdrs = 0; u8 ip_proto = 0; bool ret; @@ -714,7 +727,9 @@ proto_again: case FLOW_DISSECT_RET_OUT_GOOD: goto out_good; case FLOW_DISSECT_RET_PROTO_AGAIN: - goto proto_again; + if (skb_flow_dissect_allowed(&num_hdrs)) + goto proto_again; + goto out_good; case FLOW_DISSECT_RET_CONTINUE: case FLOW_DISSECT_RET_IPPROTO_AGAIN: break; @@ -843,9 +858,13 @@ ip_proto_again: /* Process result of IP proto processing */ switch (fdret) { case FLOW_DISSECT_RET_PROTO_AGAIN: - goto proto_again; + if (skb_flow_dissect_allowed(&num_hdrs)) + goto proto_again; + break; case FLOW_DISSECT_RET_IPPROTO_AGAIN: - goto ip_proto_again; + if (skb_flow_dissect_allowed(&num_hdrs)) + goto ip_proto_again; + break; case FLOW_DISSECT_RET_OUT_GOOD: case FLOW_DISSECT_RET_CONTINUE: break; -- cgit v1.2.3