Commit message: ip: fix IP_CHECKSUM handling

The skbs processed by ip_cmsg_recv() are not guaranteed to
be linear e.g. when sending UDP packets over loopback with
MSGMORE.
Using csum_partial() on [potentially] the whole skb len
is dangerous; instead be on the safe side and use skb_checksum().

Thanks to syzkaller team to detect the issue and provide the
reproducer.

v1 -> v2:
 - move the variable declaration in a tighter scope

Fixes: ad6f939ab193 ("ip: Add offset parameter to ip_cmsg_recv")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2017-6347
CWE: CWE-125
Vulnerability description: The ip_cmsg_recv_checksum function in net/ipv4/ip_sockglue.c in the Linux kernel before 4.10.1 has incorrect expectations about skb data layout, which allows local users to cause a denial of service (buffer over-read) or possibly have unspecified other impact via crafted system calls, as demonstrated by use of the MSG_MORE flag in conjunction with loopback UDP transmission.

Project: linux
File: ip_sockglue.c

static int do_ip_setsockopt(struct sock *sk, int level,
			    int optname, char __user *optval, unsigned int optlen)
{
	struct inet_sock *inet = inet_sk(sk);
	struct net *net = sock_net(sk);
	int val = 0, err;
	bool needs_rtnl = setsockopt_needs_rtnl(optname);

	switch (optname) {
	case IP_PKTINFO:
	case IP_RECVTTL:
	case IP_RECVOPTS:
	case IP_RECVTOS:
	case IP_RETOPTS:
	case IP_TOS:
	case IP_TTL:
	case IP_HDRINCL:
	case IP_MTU_DISCOVER:
	case IP_RECVERR:
	case IP_ROUTER_ALERT:
	case IP_FREEBIND:
	case IP_PASSSEC:
	case IP_TRANSPARENT:
	case IP_MINTTL:
	case IP_NODEFRAG:
	case IP_BIND_ADDRESS_NO_PORT:
	case IP_UNICAST_IF:
	case IP_MULTICAST_TTL:
	case IP_MULTICAST_ALL:
	case IP_MULTICAST_LOOP:
	case IP_RECVORIGDSTADDR:
	case IP_CHECKSUM:
	case IP_RECVFRAGSIZE:
		if (optlen >= sizeof(int)) {
			if (get_user(val, (int __user *) optval))
				return -EFAULT;
		} else if (optlen >= sizeof(char)) {
			unsigned char ucval;

			if (get_user(ucval, (unsigned char __user *) optval))
				return -EFAULT;
			val = (int) ucval;
		}
	}

	/* If optlen==0, it is equivalent to val == 0 */

	if (ip_mroute_opt(optname))
		return ip_mroute_setsockopt(sk, optname, optval, optlen);

	err = 0;
	if (needs_rtnl)
		rtnl_lock();
	lock_sock(sk);

	switch (optname) {
	case IP_OPTIONS:
	{
		struct ip_options_rcu *old, *opt = NULL;

		if (optlen > 40)
			goto e_inval;
		err = ip_options_get_from_user(sock_net(sk), &opt,
					       optval, optlen);
		if (err)
			break;
		old = rcu_dereference_protected(inet->inet_opt,
						lockdep_sock_is_held(sk));
		if (inet->is_icsk) {
			struct inet_connection_sock *icsk = inet_csk(sk);
#if IS_ENABLED(CONFIG_IPV6)
			if (sk->sk_family == PF_INET ||
			    (!((1 << sk->sk_state) &
			       (TCPF_LISTEN | TCPF_CLOSE)) &&
			     inet->inet_daddr != LOOPBACK4_IPV6)) {
#endif
				if (old)
					icsk->icsk_ext_hdr_len -= old->opt.optlen;
				if (opt)
					icsk->icsk_ext_hdr_len += opt->opt.optlen;
				icsk->icsk_sync_mss(sk, icsk->icsk_pmtu_cookie);
#if IS_ENABLED(CONFIG_IPV6)
			}
#endif
		}
		rcu_assign_pointer(inet->inet_opt, opt);
		if (old)
			kfree_rcu(old, rcu);
		break;
	}
	case IP_PKTINFO:
		if (val)
			inet->cmsg_flags |= IP_CMSG_PKTINFO;
		else
			inet->cmsg_flags &= ~IP_CMSG_PKTINFO;
		break;
	case IP_RECVTTL:
		if (val)
			inet->cmsg_flags |=  IP_CMSG_TTL;
		else
			inet->cmsg_flags &= ~IP_CMSG_TTL;
		break;
	case IP_RECVTOS:
		if (val)
			inet->cmsg_flags |=  IP_CMSG_TOS;
		else
			inet->cmsg_flags &= ~IP_CMSG_TOS;
		break;
	case IP_RECVOPTS:
		if (val)
			inet->cmsg_flags |=  IP_CMSG_RECVOPTS;
		else
			inet->cmsg_flags &= ~IP_CMSG_RECVOPTS;
		break;
	case IP_RETOPTS:
		if (val)
			inet->cmsg_flags |= IP_CMSG_RETOPTS;
		else
			inet->cmsg_flags &= ~IP_CMSG_RETOPTS;
		break;
	case IP_PASSSEC:
		if (val)
			inet->cmsg_flags |= IP_CMSG_PASSSEC;
		else
			inet->cmsg_flags &= ~IP_CMSG_PASSSEC;
		break;
	case IP_RECVORIGDSTADDR:
		if (val)
			inet->cmsg_flags |= IP_CMSG_ORIGDSTADDR;
		else
			inet->cmsg_flags &= ~IP_CMSG_ORIGDSTADDR;
		break;
	case IP_CHECKSUM:
		if (val) {
			if (!(inet->cmsg_flags & IP_CMSG_CHECKSUM)) {
				inet_inc_convert_csum(sk);
				inet->cmsg_flags |= IP_CMSG_CHECKSUM;
			}
		} else {
			if (inet->cmsg_flags & IP_CMSG_CHECKSUM) {
				inet_dec_convert_csum(sk);
				inet->cmsg_flags &= ~IP_CMSG_CHECKSUM;
			}
		}
		break;
	case IP_RECVFRAGSIZE:
		if (sk->sk_type != SOCK_RAW && sk->sk_type != SOCK_DGRAM)
			goto e_inval;
		if (val)
			inet->cmsg_flags |= IP_CMSG_RECVFRAGSIZE;
		else
			inet->cmsg_flags &= ~IP_CMSG_RECVFRAGSIZE;
		break;
	case IP_TOS:	/* This sets both TOS and Precedence */
		if (sk->sk_type == SOCK_STREAM) {
			val &= ~INET_ECN_MASK;
			val |= inet->tos & INET_ECN_MASK;
		}
		if (inet->tos != val) {
			inet->tos = val;
			sk->sk_priority = rt_tos2priority(val);
			sk_dst_reset(sk);
		}
		break;
	case IP_TTL:
		if (optlen < 1)
			goto e_inval;
		if (val != -1 && (val < 1 || val > 255))
			goto e_inval;
		inet->uc_ttl = val;
		break;
	case IP_HDRINCL:
		if (sk->sk_type != SOCK_RAW) {
			err = -ENOPROTOOPT;
			break;
		}
		inet->hdrincl = val ? 1 : 0;
		break;
	case IP_NODEFRAG:
		if (sk->sk_type != SOCK_RAW) {
			err = -ENOPROTOOPT;
			break;
		}
		inet->nodefrag = val ? 1 : 0;
		break;
	case IP_BIND_ADDRESS_NO_PORT:
		inet->bind_address_no_port = val ? 1 : 0;
		break;
	case IP_MTU_DISCOVER:
		if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_OMIT)
			goto e_inval;
		inet->pmtudisc = val;
		break;
	case IP_RECVERR:
		inet->recverr = !!val;
		if (!val)
			skb_queue_purge(&sk->sk_error_queue);
		break;
	case IP_MULTICAST_TTL:
		if (sk->sk_type == SOCK_STREAM)
			goto e_inval;
		if (optlen < 1)
			goto e_inval;
		if (val == -1)
			val = 1;
		if (val < 0 || val > 255)
			goto e_inval;
		inet->mc_ttl = val;
		break;
	case IP_MULTICAST_LOOP:
		if (optlen < 1)
			goto e_inval;
		inet->mc_loop = !!val;
		break;
	case IP_UNICAST_IF:
	{
		struct net_device *dev = NULL;
		int ifindex;

		if (optlen != sizeof(int))
			goto e_inval;

		ifindex = (__force int)ntohl((__force __be32)val);
		if (ifindex == 0) {
			inet->uc_index = 0;
			err = 0;
			break;
		}

		dev = dev_get_by_index(sock_net(sk), ifindex);
		err = -EADDRNOTAVAIL;
		if (!dev)
			break;
		dev_put(dev);

		err = -EINVAL;
		if (sk->sk_bound_dev_if)
			break;

		inet->uc_index = ifindex;
		err = 0;
		break;
	}
	case IP_MULTICAST_IF:
	{
		struct ip_mreqn mreq;
		struct net_device *dev = NULL;
		int midx;

		if (sk->sk_type == SOCK_STREAM)
			goto e_inval;
		/*
		 *	Check the arguments are allowable
		 */

		if (optlen < sizeof(struct in_addr))
			goto e_inval;

		err = -EFAULT;
		if (optlen >= sizeof(struct ip_mreqn)) {
			if (copy_from_user(&mreq, optval, sizeof(mreq)))
				break;
		} else {
			memset(&mreq, 0, sizeof(mreq));
			if (optlen >= sizeof(struct ip_mreq)) {
				if (copy_from_user(&mreq, optval,
						   sizeof(struct ip_mreq)))
					break;
			} else if (optlen >= sizeof(struct in_addr)) {
				if (copy_from_user(&mreq.imr_address, optval,
						   sizeof(struct in_addr)))
					break;
			}
		}

		if (!mreq.imr_ifindex) {
			if (mreq.imr_address.s_addr == htonl(INADDR_ANY)) {
				inet->mc_index = 0;
				inet->mc_addr  = 0;
				err = 0;
				break;
			}
			dev = ip_dev_find(sock_net(sk), mreq.imr_address.s_addr);
			if (dev)
				mreq.imr_ifindex = dev->ifindex;
		} else
			dev = dev_get_by_index(sock_net(sk), mreq.imr_ifindex);


		err = -EADDRNOTAVAIL;
		if (!dev)
			break;

		midx = l3mdev_master_ifindex(dev);

		dev_put(dev);

		err = -EINVAL;
		if (sk->sk_bound_dev_if &&
		    mreq.imr_ifindex != sk->sk_bound_dev_if &&
		    (!midx || midx != sk->sk_bound_dev_if))
			break;

		inet->mc_index = mreq.imr_ifindex;
		inet->mc_addr  = mreq.imr_address.s_addr;
		err = 0;
		break;
	}

	case IP_ADD_MEMBERSHIP:
	case IP_DROP_MEMBERSHIP:
	{
		struct ip_mreqn mreq;

		err = -EPROTO;
		if (inet_sk(sk)->is_icsk)
			break;

		if (optlen < sizeof(struct ip_mreq))
			goto e_inval;
		err = -EFAULT;
		if (optlen >= sizeof(struct ip_mreqn)) {
			if (copy_from_user(&mreq, optval, sizeof(mreq)))
				break;
		} else {
			memset(&mreq, 0, sizeof(mreq));
			if (copy_from_user(&mreq, optval, sizeof(struct ip_mreq)))
				break;
		}

		if (optname == IP_ADD_MEMBERSHIP)
			err = ip_mc_join_group(sk, &mreq);
		else
			err = ip_mc_leave_group(sk, &mreq);
		break;
	}
	case IP_MSFILTER:
	{
		struct ip_msfilter *msf;

		if (optlen < IP_MSFILTER_SIZE(0))
			goto e_inval;
		if (optlen > sysctl_optmem_max) {
			err = -ENOBUFS;
			break;
		}
		msf = kmalloc(optlen, GFP_KERNEL);
		if (!msf) {
			err = -ENOBUFS;
			break;
		}
		err = -EFAULT;
		if (copy_from_user(msf, optval, optlen)) {
			kfree(msf);
			break;
		}
		/* numsrc >= (1G-4) overflow in 32 bits */
		if (msf->imsf_numsrc >= 0x3ffffffcU ||
		    msf->imsf_numsrc > net->ipv4.sysctl_igmp_max_msf) {
			kfree(msf);
			err = -ENOBUFS;
			break;
		}
		if (IP_MSFILTER_SIZE(msf->imsf_numsrc) > optlen) {
			kfree(msf);
			err = -EINVAL;
			break;
		}
		err = ip_mc_msfilter(sk, msf, 0);
		kfree(msf);
		break;
	}
	case IP_BLOCK_SOURCE:
	case IP_UNBLOCK_SOURCE:
	case IP_ADD_SOURCE_MEMBERSHIP:
	case IP_DROP_SOURCE_MEMBERSHIP:
	{
		struct ip_mreq_source mreqs;
		int omode, add;

		if (optlen != sizeof(struct ip_mreq_source))
			goto e_inval;
		if (copy_from_user(&mreqs, optval, sizeof(mreqs))) {
			err = -EFAULT;
			break;
		}
		if (optname == IP_BLOCK_SOURCE) {
			omode = MCAST_EXCLUDE;
			add = 1;
		} else if (optname == IP_UNBLOCK_SOURCE) {
			omode = MCAST_EXCLUDE;
			add = 0;
		} else if (optname == IP_ADD_SOURCE_MEMBERSHIP) {
			struct ip_mreqn mreq;

			mreq.imr_multiaddr.s_addr = mreqs.imr_multiaddr;
			mreq.imr_address.s_addr = mreqs.imr_interface;
			mreq.imr_ifindex = 0;
			err = ip_mc_join_group(sk, &mreq);
			if (err && err != -EADDRINUSE)
				break;
			omode = MCAST_INCLUDE;
			add = 1;
		} else /* IP_DROP_SOURCE_MEMBERSHIP */ {
			omode = MCAST_INCLUDE;
			add = 0;
		}
		err = ip_mc_source(add, omode, sk, &mreqs, 0);
		break;
	}
	case MCAST_JOIN_GROUP:
	case MCAST_LEAVE_GROUP:
	{
		struct group_req greq;
		struct sockaddr_in *psin;
		struct ip_mreqn mreq;

		if (optlen < sizeof(struct group_req))
			goto e_inval;
		err = -EFAULT;
		if (copy_from_user(&greq, optval, sizeof(greq)))
			break;
		psin = (struct sockaddr_in *)&greq.gr_group;
		if (psin->sin_family != AF_INET)
			goto e_inval;
		memset(&mreq, 0, sizeof(mreq));
		mreq.imr_multiaddr = psin->sin_addr;
		mreq.imr_ifindex = greq.gr_interface;

		if (optname == MCAST_JOIN_GROUP)
			err = ip_mc_join_group(sk, &mreq);
		else
			err = ip_mc_leave_group(sk, &mreq);
		break;
	}
	case MCAST_JOIN_SOURCE_GROUP:
	case MCAST_LEAVE_SOURCE_GROUP:
	case MCAST_BLOCK_SOURCE:
	case MCAST_UNBLOCK_SOURCE:
	{
		struct group_source_req greqs;
		struct ip_mreq_source mreqs;
		struct sockaddr_in *psin;
		int omode, add;

		if (optlen != sizeof(struct group_source_req))
			goto e_inval;
		if (copy_from_user(&greqs, optval, sizeof(greqs))) {
			err = -EFAULT;
			break;
		}
		if (greqs.gsr_group.ss_family != AF_INET ||
		    greqs.gsr_source.ss_family != AF_INET) {
			err = -EADDRNOTAVAIL;
			break;
		}
		psin = (struct sockaddr_in *)&greqs.gsr_group;
		mreqs.imr_multiaddr = psin->sin_addr.s_addr;
		psin = (struct sockaddr_in *)&greqs.gsr_source;
		mreqs.imr_sourceaddr = psin->sin_addr.s_addr;
		mreqs.imr_interface = 0; /* use index for mc_source */

		if (optname == MCAST_BLOCK_SOURCE) {
			omode = MCAST_EXCLUDE;
			add = 1;
		} else if (optname == MCAST_UNBLOCK_SOURCE) {
			omode = MCAST_EXCLUDE;
			add = 0;
		} else if (optname == MCAST_JOIN_SOURCE_GROUP) {
			struct ip_mreqn mreq;

			psin = (struct sockaddr_in *)&greqs.gsr_group;
			mreq.imr_multiaddr = psin->sin_addr;
			mreq.imr_address.s_addr = 0;
			mreq.imr_ifindex = greqs.gsr_interface;
			err = ip_mc_join_group(sk, &mreq);
			if (err && err != -EADDRINUSE)
				break;
			greqs.gsr_interface = mreq.imr_ifindex;
			omode = MCAST_INCLUDE;
			add = 1;
		} else /* MCAST_LEAVE_SOURCE_GROUP */ {
			omode = MCAST_INCLUDE;
			add = 0;
		}
		err = ip_mc_source(add, omode, sk, &mreqs,
				   greqs.gsr_interface);
		break;
	}
	case MCAST_MSFILTER:
	{
		struct sockaddr_in *psin;
		struct ip_msfilter *msf = NULL;
		struct group_filter *gsf = NULL;
		int msize, i, ifindex;

		if (optlen < GROUP_FILTER_SIZE(0))
			goto e_inval;
		if (optlen > sysctl_optmem_max) {
			err = -ENOBUFS;
			break;
		}
		gsf = kmalloc(optlen, GFP_KERNEL);
		if (!gsf) {
			err = -ENOBUFS;
			break;
		}
		err = -EFAULT;
		if (copy_from_user(gsf, optval, optlen))
			goto mc_msf_out;

		/* numsrc >= (4G-140)/128 overflow in 32 bits */
		if (gsf->gf_numsrc >= 0x1ffffff ||
		    gsf->gf_numsrc > net->ipv4.sysctl_igmp_max_msf) {
			err = -ENOBUFS;
			goto mc_msf_out;
		}
		if (GROUP_FILTER_SIZE(gsf->gf_numsrc) > optlen) {
			err = -EINVAL;
			goto mc_msf_out;
		}
		msize = IP_MSFILTER_SIZE(gsf->gf_numsrc);
		msf = kmalloc(msize, GFP_KERNEL);
		if (!msf) {
			err = -ENOBUFS;
			goto mc_msf_out;
		}
		ifindex = gsf->gf_interface;
		psin = (struct sockaddr_in *)&gsf->gf_group;
		if (psin->sin_family != AF_INET) {
			err = -EADDRNOTAVAIL;
			goto mc_msf_out;
		}
		msf->imsf_multiaddr = psin->sin_addr.s_addr;
		msf->imsf_interface = 0;
		msf->imsf_fmode = gsf->gf_fmode;
		msf->imsf_numsrc = gsf->gf_numsrc;
		err = -EADDRNOTAVAIL;
		for (i = 0; i < gsf->gf_numsrc; ++i) {
			psin = (struct sockaddr_in *)&gsf->gf_slist[i];

			if (psin->sin_family != AF_INET)
				goto mc_msf_out;
			msf->imsf_slist[i] = psin->sin_addr.s_addr;
		}
		kfree(gsf);
		gsf = NULL;

		err = ip_mc_msfilter(sk, msf, ifindex);
mc_msf_out:
		kfree(msf);
		kfree(gsf);
		break;
	}
	case IP_MULTICAST_ALL:
		if (optlen < 1)
			goto e_inval;
		if (val != 0 && val != 1)
			goto e_inval;
		inet->mc_all = val;
		break;
	case IP_ROUTER_ALERT:
		err = ip_ra_control(sk, val ? 1 : 0, NULL);
		break;

	case IP_FREEBIND:
		if (optlen < 1)
			goto e_inval;
		inet->freebind = !!val;
		break;

	case IP_IPSEC_POLICY:
	case IP_XFRM_POLICY:
		err = -EPERM;
		if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
			break;
		err = xfrm_user_policy(sk, optname, optval, optlen);
		break;

	case IP_TRANSPARENT:
		if (!!val && !ns_capable(sock_net(sk)->user_ns, CAP_NET_RAW) &&
		    !ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)) {
			err = -EPERM;
			break;
		}
		if (optlen < 1)
			goto e_inval;
		inet->transparent = !!val;
		break;

	case IP_MINTTL:
		if (optlen < 1)
			goto e_inval;
		if (val < 0 || val > 255)
			goto e_inval;
		inet->min_ttl = val;
		break;

	default:
		err = -ENOPROTOOPT;
		break;
	}
	release_sock(sk);
	if (needs_rtnl)
		rtnl_unlock();
	return err;

e_inval:
	release_sock(sk);
	if (needs_rtnl)
		rtnl_unlock();
	return -EINVAL;
}

Project: linux
File: ip_sockglue.c

int ip_ra_control(struct sock *sk, unsigned char on,
		  void (*destructor)(struct sock *))
{
	struct ip_ra_chain *ra, *new_ra;
	struct ip_ra_chain __rcu **rap;

	if (sk->sk_type != SOCK_RAW || inet_sk(sk)->inet_num == IPPROTO_RAW)
		return -EINVAL;

	new_ra = on ? kmalloc(sizeof(*new_ra), GFP_KERNEL) : NULL;

	spin_lock_bh(&ip_ra_lock);
	for (rap = &ip_ra_chain;
	     (ra = rcu_dereference_protected(*rap,
			lockdep_is_held(&ip_ra_lock))) != NULL;
	     rap = &ra->next) {
		if (ra->sk == sk) {
			if (on) {
				spin_unlock_bh(&ip_ra_lock);
				kfree(new_ra);
				return -EADDRINUSE;
			}
			/* dont let ip_call_ra_chain() use sk again */
			ra->sk = NULL;
			RCU_INIT_POINTER(*rap, ra->next);
			spin_unlock_bh(&ip_ra_lock);

			if (ra->destructor)
				ra->destructor(sk);
			/*
			 * Delay sock_put(sk) and kfree(ra) after one rcu grace
			 * period. This guarantee ip_call_ra_chain() dont need
			 * to mess with socket refcounts.
			 */
			ra->saved_sk = sk;
			call_rcu(&ra->rcu, ip_ra_destroy_rcu);
			return 0;
		}
	}
	if (!new_ra) {
		spin_unlock_bh(&ip_ra_lock);
		return -ENOBUFS;
	}
	new_ra->sk = sk;
	new_ra->destructor = destructor;

	RCU_INIT_POINTER(new_ra->next, ra);
	rcu_assign_pointer(*rap, new_ra);
	sock_hold(sk);
	spin_unlock_bh(&ip_ra_lock);

	return 0;
}