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xfrm: policy: replace session decode with flow dissector
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xfrm needs to populate ipv4/v6 flow struct for route lookup.
In the past there were several bugs in this code:

1. callers that forget to reload header pointers after
   xfrm_decode_session() (it may pull headers).
2. bugs in decoding where accesses past skb->data occurred.

Meanwhile network core gained a packet dissector as well.
This switches xfrm to the flow dissector.

Changes since RFC:
Drop ipv6 mobiliy header support, AFAIU noone uses this.

Drop extraction of flowlabel, replaced code doesn't set it either.

Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/netdev/20230908120628.26164-3-fw@strlen.de/
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
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Florian Westphal authored and Steffen Klassert committed Oct 6, 2023
1 parent 45f87dd commit 7a02070
Showing 1 changed file with 95 additions and 158 deletions.
253 changes: 95 additions & 158 deletions net/xfrm/xfrm_policy.c
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Original file line number Diff line number Diff line change
Expand Up @@ -149,6 +149,21 @@ struct xfrm_pol_inexact_candidates {
struct hlist_head *res[XFRM_POL_CAND_MAX];
};

struct xfrm_flow_keys {
struct flow_dissector_key_basic basic;
struct flow_dissector_key_control control;
union {
struct flow_dissector_key_ipv4_addrs ipv4;
struct flow_dissector_key_ipv6_addrs ipv6;
} addrs;
struct flow_dissector_key_ip ip;
struct flow_dissector_key_icmp icmp;
struct flow_dissector_key_ports ports;
struct flow_dissector_key_keyid gre;
};

static struct flow_dissector xfrm_session_dissector __ro_after_init;

static DEFINE_SPINLOCK(xfrm_if_cb_lock);
static struct xfrm_if_cb const __rcu *xfrm_if_cb __read_mostly;

Expand Down Expand Up @@ -3367,191 +3382,74 @@ xfrm_policy_ok(const struct xfrm_tmpl *tmpl, const struct sec_path *sp, int star
}

static void
decode_session4(struct sk_buff *skb, struct flowi *fl, bool reverse)
decode_session4(const struct xfrm_flow_keys *flkeys, struct flowi *fl, bool reverse)
{
const struct iphdr *iph = ip_hdr(skb);
int ihl = iph->ihl;
u8 *xprth = skb_network_header(skb) + ihl * 4;
struct flowi4 *fl4 = &fl->u.ip4;

memset(fl4, 0, sizeof(struct flowi4));

fl4->flowi4_proto = iph->protocol;
fl4->daddr = reverse ? iph->saddr : iph->daddr;
fl4->saddr = reverse ? iph->daddr : iph->saddr;
fl4->flowi4_tos = iph->tos & ~INET_ECN_MASK;

if (!ip_is_fragment(iph)) {
switch (iph->protocol) {
case IPPROTO_UDP:
case IPPROTO_UDPLITE:
case IPPROTO_TCP:
case IPPROTO_SCTP:
case IPPROTO_DCCP:
if (xprth + 4 < skb->data ||
pskb_may_pull(skb, xprth + 4 - skb->data)) {
__be16 *ports;

xprth = skb_network_header(skb) + ihl * 4;
ports = (__be16 *)xprth;

fl4->fl4_sport = ports[!!reverse];
fl4->fl4_dport = ports[!reverse];
}
break;
case IPPROTO_ICMP:
if (xprth + 2 < skb->data ||
pskb_may_pull(skb, xprth + 2 - skb->data)) {
u8 *icmp;

xprth = skb_network_header(skb) + ihl * 4;
icmp = xprth;

fl4->fl4_icmp_type = icmp[0];
fl4->fl4_icmp_code = icmp[1];
}
break;
case IPPROTO_GRE:
if (xprth + 12 < skb->data ||
pskb_may_pull(skb, xprth + 12 - skb->data)) {
__be16 *greflags;
__be32 *gre_hdr;

xprth = skb_network_header(skb) + ihl * 4;
greflags = (__be16 *)xprth;
gre_hdr = (__be32 *)xprth;

if (greflags[0] & GRE_KEY) {
if (greflags[0] & GRE_CSUM)
gre_hdr++;
fl4->fl4_gre_key = gre_hdr[1];
}
}
break;
default:
break;
}
if (reverse) {
fl4->saddr = flkeys->addrs.ipv4.dst;
fl4->daddr = flkeys->addrs.ipv4.src;
fl4->fl4_sport = flkeys->ports.dst;
fl4->fl4_dport = flkeys->ports.src;
} else {
fl4->saddr = flkeys->addrs.ipv4.src;
fl4->daddr = flkeys->addrs.ipv4.dst;
fl4->fl4_sport = flkeys->ports.src;
fl4->fl4_dport = flkeys->ports.dst;
}

fl4->flowi4_proto = flkeys->basic.ip_proto;
fl4->flowi4_tos = flkeys->ip.tos;
fl4->fl4_icmp_type = flkeys->icmp.type;
fl4->fl4_icmp_type = flkeys->icmp.code;
fl4->fl4_gre_key = flkeys->gre.keyid;
}

#if IS_ENABLED(CONFIG_IPV6)
static void
decode_session6(struct sk_buff *skb, struct flowi *fl, bool reverse)
decode_session6(const struct xfrm_flow_keys *flkeys, struct flowi *fl, bool reverse)
{
struct flowi6 *fl6 = &fl->u.ip6;
int onlyproto = 0;
const struct ipv6hdr *hdr = ipv6_hdr(skb);
u32 offset = sizeof(*hdr);
struct ipv6_opt_hdr *exthdr;
const unsigned char *nh = skb_network_header(skb);
u16 nhoff = IP6CB(skb)->nhoff;
u8 nexthdr;

if (!nhoff)
nhoff = offsetof(struct ipv6hdr, nexthdr);

nexthdr = nh[nhoff];

memset(fl6, 0, sizeof(struct flowi6));

fl6->daddr = reverse ? hdr->saddr : hdr->daddr;
fl6->saddr = reverse ? hdr->daddr : hdr->saddr;

while (nh + offset + sizeof(*exthdr) < skb->data ||
pskb_may_pull(skb, nh + offset + sizeof(*exthdr) - skb->data)) {
nh = skb_network_header(skb);
exthdr = (struct ipv6_opt_hdr *)(nh + offset);

switch (nexthdr) {
case NEXTHDR_FRAGMENT:
onlyproto = 1;
fallthrough;
case NEXTHDR_ROUTING:
case NEXTHDR_HOP:
case NEXTHDR_DEST:
offset += ipv6_optlen(exthdr);
nexthdr = exthdr->nexthdr;
break;
case IPPROTO_UDP:
case IPPROTO_UDPLITE:
case IPPROTO_TCP:
case IPPROTO_SCTP:
case IPPROTO_DCCP:
if (!onlyproto && (nh + offset + 4 < skb->data ||
pskb_may_pull(skb, nh + offset + 4 - skb->data))) {
__be16 *ports;

nh = skb_network_header(skb);
ports = (__be16 *)(nh + offset);
fl6->fl6_sport = ports[!!reverse];
fl6->fl6_dport = ports[!reverse];
}
fl6->flowi6_proto = nexthdr;
return;
case IPPROTO_ICMPV6:
if (!onlyproto && (nh + offset + 2 < skb->data ||
pskb_may_pull(skb, nh + offset + 2 - skb->data))) {
u8 *icmp;

nh = skb_network_header(skb);
icmp = (u8 *)(nh + offset);
fl6->fl6_icmp_type = icmp[0];
fl6->fl6_icmp_code = icmp[1];
}
fl6->flowi6_proto = nexthdr;
return;
case IPPROTO_GRE:
if (!onlyproto &&
(nh + offset + 12 < skb->data ||
pskb_may_pull(skb, nh + offset + 12 - skb->data))) {
struct gre_base_hdr *gre_hdr;
__be32 *gre_key;

nh = skb_network_header(skb);
gre_hdr = (struct gre_base_hdr *)(nh + offset);
gre_key = (__be32 *)(gre_hdr + 1);

if (gre_hdr->flags & GRE_KEY) {
if (gre_hdr->flags & GRE_CSUM)
gre_key++;
fl6->fl6_gre_key = *gre_key;
}
}
fl6->flowi6_proto = nexthdr;
return;

#if IS_ENABLED(CONFIG_IPV6_MIP6)
case IPPROTO_MH:
offset += ipv6_optlen(exthdr);
if (!onlyproto && (nh + offset + 3 < skb->data ||
pskb_may_pull(skb, nh + offset + 3 - skb->data))) {
struct ip6_mh *mh;

nh = skb_network_header(skb);
mh = (struct ip6_mh *)(nh + offset);
fl6->fl6_mh_type = mh->ip6mh_type;
}
fl6->flowi6_proto = nexthdr;
return;
#endif
default:
fl6->flowi6_proto = nexthdr;
return;
}
if (reverse) {
fl6->saddr = flkeys->addrs.ipv6.dst;
fl6->daddr = flkeys->addrs.ipv6.src;
fl6->fl6_sport = flkeys->ports.dst;
fl6->fl6_dport = flkeys->ports.src;
} else {
fl6->saddr = flkeys->addrs.ipv6.src;
fl6->daddr = flkeys->addrs.ipv6.dst;
fl6->fl6_sport = flkeys->ports.src;
fl6->fl6_dport = flkeys->ports.dst;
}

fl6->flowi6_proto = flkeys->basic.ip_proto;
fl6->fl6_icmp_type = flkeys->icmp.type;
fl6->fl6_icmp_type = flkeys->icmp.code;
fl6->fl6_gre_key = flkeys->gre.keyid;
}
#endif

int __xfrm_decode_session(struct net *net, struct sk_buff *skb, struct flowi *fl,
unsigned int family, int reverse)
{
struct xfrm_flow_keys flkeys;

memset(&flkeys, 0, sizeof(flkeys));
__skb_flow_dissect(net, skb, &xfrm_session_dissector, &flkeys,
NULL, 0, 0, 0, FLOW_DISSECTOR_F_STOP_AT_ENCAP);

switch (family) {
case AF_INET:
decode_session4(skb, fl, reverse);
decode_session4(&flkeys, fl, reverse);
break;
#if IS_ENABLED(CONFIG_IPV6)
case AF_INET6:
decode_session6(skb, fl, reverse);
decode_session6(&flkeys, fl, reverse);
break;
#endif
default:
Expand Down Expand Up @@ -4253,8 +4151,47 @@ static struct pernet_operations __net_initdata xfrm_net_ops = {
.exit = xfrm_net_exit,
};

static const struct flow_dissector_key xfrm_flow_dissector_keys[] = {
{
.key_id = FLOW_DISSECTOR_KEY_CONTROL,
.offset = offsetof(struct xfrm_flow_keys, control),
},
{
.key_id = FLOW_DISSECTOR_KEY_BASIC,
.offset = offsetof(struct xfrm_flow_keys, basic),
},
{
.key_id = FLOW_DISSECTOR_KEY_IPV4_ADDRS,
.offset = offsetof(struct xfrm_flow_keys, addrs.ipv4),
},
{
.key_id = FLOW_DISSECTOR_KEY_IPV6_ADDRS,
.offset = offsetof(struct xfrm_flow_keys, addrs.ipv6),
},
{
.key_id = FLOW_DISSECTOR_KEY_PORTS,
.offset = offsetof(struct xfrm_flow_keys, ports),
},
{
.key_id = FLOW_DISSECTOR_KEY_GRE_KEYID,
.offset = offsetof(struct xfrm_flow_keys, gre),
},
{
.key_id = FLOW_DISSECTOR_KEY_IP,
.offset = offsetof(struct xfrm_flow_keys, ip),
},
{
.key_id = FLOW_DISSECTOR_KEY_ICMP,
.offset = offsetof(struct xfrm_flow_keys, icmp),
},
};

void __init xfrm_init(void)
{
skb_flow_dissector_init(&xfrm_session_dissector,
xfrm_flow_dissector_keys,
ARRAY_SIZE(xfrm_flow_dissector_keys));

register_pernet_subsys(&xfrm_net_ops);
xfrm_dev_init();
xfrm_input_init();
Expand Down

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