ipv6: make ipv6_renew_options() interrupt/kernel safe

At present the ipv6_renew_options_kern() function ends up calling into
access_ok() which is problematic if done from inside an interrupt as
access_ok() calls WARN_ON_IN_IRQ() on some (all?) architectures
(x86-64 is affected). Example warning/backtrace is shown below:

WARNING: CPU: 1 PID: 3144 at lib/usercopy.c:11 _copy_from_user+0x85/0x90
...
Call Trace:
<IRQ>
ipv6_renew_option+0xb2/0xf0
ipv6_renew_options+0x26a/0x340
ipv6_renew_options_kern+0x2c/0x40
calipso_req_setattr+0x72/0xe0
netlbl_req_setattr+0x126/0x1b0
selinux_netlbl_inet_conn_request+0x80/0x100
selinux_inet_conn_request+0x6d/0xb0
security_inet_conn_request+0x32/0x50
tcp_conn_request+0x35f/0xe00
? __lock_acquire+0x250/0x16c0
? selinux_socket_sock_rcv_skb+0x1ae/0x210
? tcp_rcv_state_process+0x289/0x106b
tcp_rcv_state_process+0x289/0x106b
? tcp_v6_do_rcv+0x1a7/0x3c0
tcp_v6_do_rcv+0x1a7/0x3c0
tcp_v6_rcv+0xc82/0xcf0
ip6_input_finish+0x10d/0x690
ip6_input+0x45/0x1e0
? ip6_rcv_finish+0x1d0/0x1d0
ipv6_rcv+0x32b/0x880
? ip6_make_skb+0x1e0/0x1e0
__netif_receive_skb_core+0x6f2/0xdf0
? process_backlog+0x85/0x250
? process_backlog+0x85/0x250
? process_backlog+0xec/0x250
process_backlog+0xec/0x250
net_rx_action+0x153/0x480
__do_softirq+0xd9/0x4f7
do_softirq_own_stack+0x2a/0x40
</IRQ>
...

While not present in the backtrace, ipv6_renew_option() ends up calling
access_ok() via the following chain:

access_ok()
_copy_from_user()
copy_from_user()
ipv6_renew_option()

The fix presented in this patch is to perform the userspace copy
earlier in the call chain such that it is only called when the option
data is actually coming from userspace; that place is
do_ipv6_setsockopt(). Not only does this solve the problem seen in
the backtrace above, it also allows us to simplify the code quite a
bit by removing ipv6_renew_options_kern() completely. We also take
this opportunity to cleanup ipv6_renew_options()/ipv6_renew_option()
a small amount as well.

This patch is heavily based on a rough patch by Al Viro. I've taken
his original patch, converted a kmemdup() call in do_ipv6_setsockopt()
to a memdup_user() call, made better use of the e_inval jump target in
the same function, and cleaned up the use ipv6_renew_option() by
ipv6_renew_options().

CC: Al Viro <[e-mail]>
Signed-off-by: Paul Moore <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ipv6.h

···
 struct ipv6_txoptions *ipv6_renew_options(struct sock *sk,
 					  struct ipv6_txoptions *opt,
 					  int newtype,
-					  struct ipv6_opt_hdr __user *newopt,
-					  int newoptlen);
-struct ipv6_txoptions *
-ipv6_renew_options_kern(struct sock *sk,
-			struct ipv6_txoptions *opt,
-			int newtype,
-			struct ipv6_opt_hdr *newopt,
-			int newoptlen);
+					  struct ipv6_opt_hdr *newopt);
 struct ipv6_txoptions *ipv6_fixup_options(struct ipv6_txoptions *opt_space,
 					  struct ipv6_txoptions *opt);
 

net/ipv6/calipso.c

···
 {
 	struct ipv6_txoptions *old = txopt_get(inet6_sk(sk)), *txopts;
 
-	txopts = ipv6_renew_options_kern(sk, old, IPV6_HOPOPTS,
-					 hop, hop ? ipv6_optlen(hop) : 0);
+	txopts = ipv6_renew_options(sk, old, IPV6_HOPOPTS, hop);
 	txopt_put(old);
 	if (IS_ERR(txopts))
 		return PTR_ERR(txopts);
···
 	if (IS_ERR(new))
 		return PTR_ERR(new);
 
-	txopts = ipv6_renew_options_kern(sk, req_inet->ipv6_opt, IPV6_HOPOPTS,
-					 new, new ? ipv6_optlen(new) : 0);
+	txopts = ipv6_renew_options(sk, req_inet->ipv6_opt, IPV6_HOPOPTS, new);
 
 	kfree(new);
 
···
 	if (calipso_opt_del(req_inet->ipv6_opt->hopopt, &new))
 		return; /* Nothing to do */
 
-	txopts = ipv6_renew_options_kern(sk, req_inet->ipv6_opt, IPV6_HOPOPTS,
-					 new, new ? ipv6_optlen(new) : 0);
+	txopts = ipv6_renew_options(sk, req_inet->ipv6_opt, IPV6_HOPOPTS, new);
 
 	if (!IS_ERR(txopts)) {
 		txopts = xchg(&req_inet->ipv6_opt, txopts);

net/ipv6/exthdrs.c

···
 }
 EXPORT_SYMBOL_GPL(ipv6_dup_options);
 
-static int ipv6_renew_option(void *ohdr,
-			     struct ipv6_opt_hdr __user *newopt, int newoptlen,
-			     int inherit,
-			     struct ipv6_opt_hdr **hdr,
-			     char **p)
+static void ipv6_renew_option(int renewtype,
+			      struct ipv6_opt_hdr **dest,
+			      struct ipv6_opt_hdr *old,
+			      struct ipv6_opt_hdr *new,
+			      int newtype, char **p)
 {
-	if (inherit) {
-		if (ohdr) {
-			memcpy(*p, ohdr, ipv6_optlen((struct ipv6_opt_hdr *)ohdr));
-			*hdr = (struct ipv6_opt_hdr *)*p;
-			*p += CMSG_ALIGN(ipv6_optlen(*hdr));
-		}
-	} else {
-		if (newopt) {
-			if (copy_from_user(*p, newopt, newoptlen))
-				return -EFAULT;
-			*hdr = (struct ipv6_opt_hdr *)*p;
-			if (ipv6_optlen(*hdr) > newoptlen)
-				return -EINVAL;
-			*p += CMSG_ALIGN(newoptlen);
-		}
-	}
-	return 0;
+	struct ipv6_opt_hdr *src;
+
+	src = (renewtype == newtype ? new : old);
+	if (!src)
+		return;
+
+	memcpy(*p, src, ipv6_optlen(src));
+	*dest = (struct ipv6_opt_hdr *)*p;
+	*p += CMSG_ALIGN(ipv6_optlen(*dest));
 }
 
 /**
···
  */
 struct ipv6_txoptions *
 ipv6_renew_options(struct sock *sk, struct ipv6_txoptions *opt,
-		   int newtype,
-		   struct ipv6_opt_hdr __user *newopt, int newoptlen)
+		   int newtype, struct ipv6_opt_hdr *newopt)
 {
 	int tot_len = 0;
 	char *p;
 	struct ipv6_txoptions *opt2;
-	int err;
 
 	if (opt) {
 		if (newtype != IPV6_HOPOPTS && opt->hopopt)
···
 			tot_len += CMSG_ALIGN(ipv6_optlen(opt->dst1opt));
 	}
 
-	if (newopt && newoptlen)
-		tot_len += CMSG_ALIGN(newoptlen);
+	if (newopt)
+		tot_len += CMSG_ALIGN(ipv6_optlen(newopt));
 
 	if (!tot_len)
 		return NULL;
···
 	opt2->tot_len = tot_len;
 	p = (char *)(opt2 + 1);
 
-	err = ipv6_renew_option(opt ? opt->hopopt : NULL, newopt, newoptlen,
-				newtype != IPV6_HOPOPTS,
-				&opt2->hopopt, &p);
-	if (err)
-		goto out;
-
-	err = ipv6_renew_option(opt ? opt->dst0opt : NULL, newopt, newoptlen,
-				newtype != IPV6_RTHDRDSTOPTS,
-				&opt2->dst0opt, &p);
-	if (err)
-		goto out;
-
-	err = ipv6_renew_option(opt ? opt->srcrt : NULL, newopt, newoptlen,
-				newtype != IPV6_RTHDR,
-				(struct ipv6_opt_hdr **)&opt2->srcrt, &p);
-	if (err)
-		goto out;
-
-	err = ipv6_renew_option(opt ? opt->dst1opt : NULL, newopt, newoptlen,
-				newtype != IPV6_DSTOPTS,
-				&opt2->dst1opt, &p);
-	if (err)
-		goto out;
+	ipv6_renew_option(IPV6_HOPOPTS, &opt2->hopopt,
+			  (opt ? opt->hopopt : NULL),
+			  newopt, newtype, &p);
+	ipv6_renew_option(IPV6_RTHDRDSTOPTS, &opt2->dst0opt,
+			  (opt ? opt->dst0opt : NULL),
+			  newopt, newtype, &p);
+	ipv6_renew_option(IPV6_RTHDR,
+			  (struct ipv6_opt_hdr **)&opt2->srcrt,
+			  (opt ? (struct ipv6_opt_hdr *)opt->srcrt : NULL),
+			  newopt, newtype, &p);
+	ipv6_renew_option(IPV6_DSTOPTS, &opt2->dst1opt,
+			  (opt ? opt->dst1opt : NULL),
+			  newopt, newtype, &p);
 
 	opt2->opt_nflen = (opt2->hopopt ? ipv6_optlen(opt2->hopopt) : 0) +
 			  (opt2->dst0opt ? ipv6_optlen(opt2->dst0opt) : 0) +
···
 	opt2->opt_flen = (opt2->dst1opt ? ipv6_optlen(opt2->dst1opt) : 0);
 
 	return opt2;
-out:
-	sock_kfree_s(sk, opt2, opt2->tot_len);
-	return ERR_PTR(err);
-}
-
-/**
- * ipv6_renew_options_kern - replace a specific ext hdr with a new one.
- *
- * @sk: sock from which to allocate memory
- * @opt: original options
- * @newtype: option type to replace in @opt
- * @newopt: new option of type @newtype to replace (kernel-mem)
- * @newoptlen: length of @newopt
- *
- * See ipv6_renew_options().  The difference is that @newopt is
- * kernel memory, rather than user memory.
- */
-struct ipv6_txoptions *
-ipv6_renew_options_kern(struct sock *sk, struct ipv6_txoptions *opt,
-			int newtype, struct ipv6_opt_hdr *newopt,
-			int newoptlen)
-{
-	struct ipv6_txoptions *ret_val;
-	const mm_segment_t old_fs = get_fs();
-
-	set_fs(KERNEL_DS);
-	ret_val = ipv6_renew_options(sk, opt, newtype,
-				     (struct ipv6_opt_hdr __user *)newopt,
-				     newoptlen);
-	set_fs(old_fs);
-	return ret_val;
 }
 
 struct ipv6_txoptions *ipv6_fixup_options(struct ipv6_txoptions *opt_space,

net/ipv6/ipv6_sockglue.c

···
 	case IPV6_DSTOPTS:
 	{
 		struct ipv6_txoptions *opt;
+		struct ipv6_opt_hdr *new = NULL;
+
+		/* hop-by-hop / destination options are privileged option */
+		retv = -EPERM;
+		if (optname != IPV6_RTHDR && !ns_capable(net->user_ns, CAP_NET_RAW))
+			break;
 
 		/* remove any sticky options header with a zero option
 		 * length, per RFC3542.
···
 		else if (optlen < sizeof(struct ipv6_opt_hdr) ||
 			 optlen & 0x7 || optlen > 8 * 255)
 			goto e_inval;
-
-		/* hop-by-hop / destination options are privileged option */
-		retv = -EPERM;
-		if (optname != IPV6_RTHDR && !ns_capable(net->user_ns, CAP_NET_RAW))
-			break;
+		else {
+			new = memdup_user(optval, optlen);
+			if (IS_ERR(new)) {
+				retv = PTR_ERR(new);
+				break;
+			}
+			if (unlikely(ipv6_optlen(new) > optlen)) {
+				kfree(new);
+				goto e_inval;
+			}
+		}
 
 		opt = rcu_dereference_protected(np->opt,
 						lockdep_sock_is_held(sk));
-		opt = ipv6_renew_options(sk, opt, optname,
-					 (struct ipv6_opt_hdr __user *)optval,
-					 optlen);
+		opt = ipv6_renew_options(sk, opt, optname, new);
+		kfree(new);
 		if (IS_ERR(opt)) {
 			retv = PTR_ERR(opt);
 			break;