net/ipv4/gre_demux.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  *  GRE over IPv4 demultiplexer driver
0004  *
0005  *  Authors: Dmitry Kozlov (xeb@mail.ru)
0006  */
0007
0008 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0009
0010 #include <linux/module.h>
0011 #include <linux/if.h>
0012 #include <linux/icmp.h>
0013 #include <linux/kernel.h>
0014 #include <linux/kmod.h>
0015 #include <linux/skbuff.h>
0016 #include <linux/in.h>
0017 #include <linux/ip.h>
0018 #include <linux/netdevice.h>
0019 #include <linux/if_tunnel.h>
0020 #include <linux/spinlock.h>
0021 #include <net/protocol.h>
0022 #include <net/gre.h>
0023 #include <net/erspan.h>
0024
0025 #include <net/icmp.h>
0026 #include <net/route.h>
0027 #include <net/xfrm.h>
0028
0029 static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
0030
0031 int gre_add_protocol(const struct gre_protocol *proto, u8 version)
0032 {
0033     if (version >= GREPROTO_MAX)
0034         return -EINVAL;
0035
0036     return (cmpxchg((const struct gre_protocol **)&gre_proto[version], NULL, proto) == NULL) ?
0037         0 : -EBUSY;
0038 }
0039 EXPORT_SYMBOL_GPL(gre_add_protocol);
0040
0041 int gre_del_protocol(const struct gre_protocol *proto, u8 version)
0042 {
0043     int ret;
0044
0045     if (version >= GREPROTO_MAX)
0046         return -EINVAL;
0047
0048     ret = (cmpxchg((const struct gre_protocol **)&gre_proto[version], proto, NULL) == proto) ?
0049         0 : -EBUSY;
0050
0051     if (ret)
0052         return ret;
0053
0054     synchronize_rcu();
0055     return 0;
0056 }
0057 EXPORT_SYMBOL_GPL(gre_del_protocol);
0058
0059 /* Fills in tpi and returns header length to be pulled.
0060  * Note that caller must use pskb_may_pull() before pulling GRE header.
0061  */
0062 int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
0063              bool *csum_err, __be16 proto, int nhs)
0064 {
0065     const struct gre_base_hdr *greh;
0066     __be32 *options;
0067     int hdr_len;
0068
0069     if (unlikely(!pskb_may_pull(skb, nhs + sizeof(struct gre_base_hdr))))
0070         return -EINVAL;
0071
0072     greh = (struct gre_base_hdr *)(skb->data + nhs);
0073     if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
0074         return -EINVAL;
0075
0076     tpi->flags = gre_flags_to_tnl_flags(greh->flags);
0077     hdr_len = gre_calc_hlen(tpi->flags);
0078
0079     if (!pskb_may_pull(skb, nhs + hdr_len))
0080         return -EINVAL;
0081
0082     greh = (struct gre_base_hdr *)(skb->data + nhs);
0083     tpi->proto = greh->protocol;
0084
0085     options = (__be32 *)(greh + 1);
0086     if (greh->flags & GRE_CSUM) {
0087         if (!skb_checksum_simple_validate(skb)) {
0088             skb_checksum_try_convert(skb, IPPROTO_GRE,
0089                          null_compute_pseudo);
0090         } else if (csum_err) {
0091             *csum_err = true;
0092             return -EINVAL;
0093         }
0094
0095         options++;
0096     }
0097
0098     if (greh->flags & GRE_KEY) {
0099         tpi->key = *options;
0100         options++;
0101     } else {
0102         tpi->key = 0;
0103     }
0104     if (unlikely(greh->flags & GRE_SEQ)) {
0105         tpi->seq = *options;
0106         options++;
0107     } else {
0108         tpi->seq = 0;
0109     }
0110     /* WCCP version 1 and 2 protocol decoding.
0111      * - Change protocol to IPv4/IPv6
0112      * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
0113      */
0114     if (greh->flags == 0 && tpi->proto == htons(ETH_P_WCCP)) {
0115         u8 _val, *val;
0116
0117         val = skb_header_pointer(skb, nhs + hdr_len,
0118                      sizeof(_val), &_val);
0119         if (!val)
0120             return -EINVAL;
0121         tpi->proto = proto;
0122         if ((*val & 0xF0) != 0x40)
0123             hdr_len += 4;
0124     }
0125     tpi->hdr_len = hdr_len;
0126
0127     /* ERSPAN ver 1 and 2 protocol sets GRE key field
0128      * to 0 and sets the configured key in the
0129      * inner erspan header field
0130      */
0131     if ((greh->protocol == htons(ETH_P_ERSPAN) && hdr_len != 4) ||
0132         greh->protocol == htons(ETH_P_ERSPAN2)) {
0133         struct erspan_base_hdr *ershdr;
0134
0135         if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
0136             return -EINVAL;
0137
0138         ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
0139         tpi->key = cpu_to_be32(get_session_id(ershdr));
0140     }
0141
0142     return hdr_len;
0143 }
0144 EXPORT_SYMBOL(gre_parse_header);
0145
0146 static int gre_rcv(struct sk_buff *skb)
0147 {
0148     const struct gre_protocol *proto;
0149     u8 ver;
0150     int ret;
0151
0152     if (!pskb_may_pull(skb, 12))
0153         goto drop;
0154
0155     ver = skb->data[1]&0x7f;
0156     if (ver >= GREPROTO_MAX)
0157         goto drop;
0158
0159     rcu_read_lock();
0160     proto = rcu_dereference(gre_proto[ver]);
0161     if (!proto || !proto->handler)
0162         goto drop_unlock;
0163     ret = proto->handler(skb);
0164     rcu_read_unlock();
0165     return ret;
0166
0167 drop_unlock:
0168     rcu_read_unlock();
0169 drop:
0170     kfree_skb(skb);
0171     return NET_RX_DROP;
0172 }
0173
0174 static int gre_err(struct sk_buff *skb, u32 info)
0175 {
0176     const struct gre_protocol *proto;
0177     const struct iphdr *iph = (const struct iphdr *)skb->data;
0178     u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
0179     int err = 0;
0180
0181     if (ver >= GREPROTO_MAX)
0182         return -EINVAL;
0183
0184     rcu_read_lock();
0185     proto = rcu_dereference(gre_proto[ver]);
0186     if (proto && proto->err_handler)
0187         proto->err_handler(skb, info);
0188     else
0189         err = -EPROTONOSUPPORT;
0190     rcu_read_unlock();
0191
0192     return err;
0193 }
0194
0195 static const struct net_protocol net_gre_protocol = {
0196     .handler     = gre_rcv,
0197     .err_handler = gre_err,
0198 };
0199
0200 static int __init gre_init(void)
0201 {
0202     pr_info("GRE over IPv4 demultiplexor driver\n");
0203
0204     if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
0205         pr_err("can't add protocol\n");
0206         return -EAGAIN;
0207     }
0208     return 0;
0209 }
0210
0211 static void __exit gre_exit(void)
0212 {
0213     inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
0214 }
0215
0216 module_init(gre_init);
0217 module_exit(gre_exit);
0218
0219 MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
0220 MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
0221 MODULE_LICENSE("GPL");