* [PATCH] [RFC] net-ipv6: ipv4 emulation support
@ 2026-07-13 8:16 Maciej Żenczykowski
2026-07-13 9:05 ` Maciej Żenczykowski
0 siblings, 1 reply; 2+ messages in thread
From: Maciej Żenczykowski @ 2026-07-13 8:16 UTC (permalink / raw)
To: Maciej Żenczykowski
Cc: Linux Network Development Mailing List,
Fernando Fernandez Mancera, Maciej Żenczykowski
Change-Id: Ibab1a59f4730f3fd0a7d14fffc5100a02a170ac6
---
gconfigs/Gconfig.net-configs.ipv6 | 2 +
include/linux/ipv6.h | 6 +-
include/linux/socket.h | 5 +-
include/net/compat.h | 2 +-
net/compat.c | 6 +-
net/core/iovec.c | 4 +-
net/ipv6/Kconfig | 19 +++
net/ipv6/af_inet6.c | 5 +
net/ipv6/ipv6_sockglue.c | 8 +-
net/ipv6/sysctl_net_ipv6.c | 26 ++++
net/socket.c | 211 +++++++++++++++++++++++++++---
11 files changed, 260 insertions(+), 34 deletions(-)
create mode 100644 gconfigs/Gconfig.net-configs.ipv6
diff --git a/gconfigs/Gconfig.net-configs.ipv6 b/gconfigs/Gconfig.net-configs.ipv6
new file mode 100644
index 000000000000..9eb5694bae8e
--- /dev/null
+++ b/gconfigs/Gconfig.net-configs.ipv6
@@ -0,0 +1,2 @@
+CONFIG_IPV6_IPV4_EMULATE=y
+CONFIG_IPV6_IPV4_EMULATE_SYSCTL_DEFAULT=y
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index ff560537dd61..8bc5306094b5 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -157,11 +157,13 @@ struct ipv6_pinfo {
#if defined(__BIG_ENDIAN_BITFIELD)
/* Packed in 16bits. */
__s16 mcast_hops:9;
- __u16 __unused_2:6,
+ __u16 __unused_2:5,
+ ipv4emu:1,
mc_loop:1;
#else
__u16 mc_loop:1,
- __unused_2:6;
+ ipv4emu:1,
+ __unused_2:5;
__s16 mcast_hops:9;
#endif
int ucast_oif;
diff --git a/include/linux/socket.h b/include/linux/socket.h
index bb9b83640070..4ae959a3443b 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -8,6 +8,7 @@
#include <linux/types.h> /* pid_t */
#include <linux/compiler.h> /* __user */
#include <uapi/linux/socket.h>
+struct sock; /* from net/sock.h */
struct pid;
struct cred;
@@ -312,8 +313,8 @@ extern int csum_partial_copy_fromiovecend(unsigned char *kdata,
extern unsigned long iov_pages(const struct iovec *iov, int offset,
unsigned long nr_segs);
-extern int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode);
-extern int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *kaddr);
+extern int verify_iovec(struct sock *sk, struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode);
+extern int move_addr_to_kernel(struct sock *sk, void __user *uaddr, int *ulen, struct sockaddr_storage *kaddr);
extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data);
struct timespec;
diff --git a/include/net/compat.h b/include/net/compat.h
index 3b603b199c01..b9ee7aa5a31f 100644
--- a/include/net/compat.h
+++ b/include/net/compat.h
@@ -41,7 +41,7 @@ int compat_sock_get_timestampns(struct sock *, struct timespec __user *);
#endif /* defined(CONFIG_COMPAT) */
int get_compat_msghdr(struct msghdr *, struct compat_msghdr __user *);
-int verify_compat_iovec(struct msghdr *, struct iovec *,
+int verify_compat_iovec(struct sock *, struct msghdr *, struct iovec *,
struct sockaddr_storage *, int);
asmlinkage long compat_sys_sendmsg(int, struct compat_msghdr __user *,
unsigned int);
diff --git a/net/compat.c b/net/compat.c
index bc8aeefddf3f..f66bd6552204 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -80,15 +80,15 @@ int get_compat_msghdr(struct msghdr *kmsg, struct compat_msghdr __user *umsg)
}
/* I've named the args so it is easy to tell whose space the pointers are in. */
-int verify_compat_iovec(struct msghdr *kern_msg, struct iovec *kern_iov,
+int verify_compat_iovec(struct sock *sk, struct msghdr *kern_msg, struct iovec *kern_iov,
struct sockaddr_storage *kern_address, int mode)
{
int tot_len;
if (kern_msg->msg_name && kern_msg->msg_namelen) {
if (mode == VERIFY_READ) {
- int err = move_addr_to_kernel(kern_msg->msg_name,
- kern_msg->msg_namelen,
+ int err = move_addr_to_kernel(sk, kern_msg->msg_name,
+ &kern_msg->msg_namelen,
kern_address);
if (err < 0)
return err;
diff --git a/net/core/iovec.c b/net/core/iovec.c
index e1ec45ab1e63..a7a393cae2a7 100644
--- a/net/core/iovec.c
+++ b/net/core/iovec.c
@@ -35,7 +35,7 @@
* in any case.
*/
-int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode)
+int verify_iovec(struct sock *sk, struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode)
{
int size, ct, err;
@@ -43,7 +43,7 @@ int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr_storage *a
if (mode == VERIFY_READ) {
void __user *namep;
namep = (void __user __force *) m->msg_name;
- err = move_addr_to_kernel(namep, m->msg_namelen,
+ err = move_addr_to_kernel(sk, namep, &m->msg_namelen,
address);
if (err < 0)
return err;
diff --git a/net/ipv6/Kconfig b/net/ipv6/Kconfig
index 438a73aa777c..69924a6c2257 100644
--- a/net/ipv6/Kconfig
+++ b/net/ipv6/Kconfig
@@ -21,6 +21,25 @@ menuconfig IPV6
if IPV6
+config IPV6_IPV4_EMULATE
+ bool "IPv6: IPv4 socket interface emulation support"
+ default n
+ depends on IPV6=y
+ ---help---
+ Whether to include support code which allows using a kernel IPv6
+ socket from userspace as if it was an IPv4 socket.
+
+ ie. this is a userspace-kernel IP address translation shim layer.
+
+config IPV6_IPV4_EMULATE_SYSCTL_DEFAULT
+ bool "IPv6: IPv4 socket emulation - default sysctl setting"
+ default n
+ depends on IPV6_IPV4_EMULATE
+ ---help---
+ Default value for /proc/sys/net/ipv6/ipv4_emulation
+ The content of this sysctl file determines whether userspace asking
+ for IPv4 sockets gets IPv6 sockets with IPv4 emulation turned on.
+
config IPV6_ROUTER_PREF
bool "IPv6: Router Preference (RFC 4191) support"
---help---
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index e8c4400f23e9..4f08abdf06e0 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -476,6 +476,11 @@ int inet6_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
struct sock *sk = sock->sk;
struct net *net = sock_net(sk);
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ if (inet6_sk(sk)->ipv4emu)
+ return inet_ioctl(sock, cmd, arg);
+#endif
+
switch (cmd) {
case SIOCGSTAMP:
return sock_get_timestamp(sk, (struct timeval __user *)arg);
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index e1a9583bb419..2e97c6d55b62 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -857,7 +857,7 @@ int ipv6_setsockopt(struct sock *sk, int level, int optname,
if (level == SOL_IP && sk->sk_type != SOCK_RAW)
return udp_prot.setsockopt(sk, level, optname, optval, optlen);
- if (level != SOL_IPV6)
+ if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
return -ENOPROTOOPT;
err = do_ipv6_setsockopt(sk, level, optname, optval, optlen);
@@ -888,7 +888,7 @@ int compat_ipv6_setsockopt(struct sock *sk, int level, int optname,
return udp_prot.setsockopt(sk, level, optname, optval, optlen);
}
- if (level != SOL_IPV6)
+ if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
return -ENOPROTOOPT;
if (optname >= MCAST_JOIN_GROUP && optname <= MCAST_MSFILTER)
@@ -1297,7 +1297,7 @@ int ipv6_getsockopt(struct sock *sk, int level, int optname,
if (level == SOL_IP && sk->sk_type != SOCK_RAW)
return udp_prot.getsockopt(sk, level, optname, optval, optlen);
- if (level != SOL_IPV6)
+ if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
return -ENOPROTOOPT;
err = do_ipv6_getsockopt(sk, level, optname, optval, optlen, 0);
@@ -1334,7 +1334,7 @@ int compat_ipv6_getsockopt(struct sock *sk, int level, int optname,
return udp_prot.getsockopt(sk, level, optname, optval, optlen);
}
- if (level != SOL_IPV6)
+ if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
return -ENOPROTOOPT;
if (optname == MCAST_MSFILTER)
diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index c5c10fafcfe2..0ab6a8d5aa57 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -6,6 +6,7 @@
*/
#include <linux/mm.h>
+#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/in6.h>
#include <linux/ipv6.h>
@@ -18,6 +19,20 @@
static int one = 1;
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+static int zero;
+
+# if defined(CONFIG_IPV6_IPV4_EMULATE_SYSCTL_DEFAULT)
+bool sysctl_ipv4_emulation = true;
+# else
+bool sysctl_ipv4_emulation = false;
+# endif
+
+module_param_named(ipv4_emulation, sysctl_ipv4_emulation, bool, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(ipv4_emulation,
+ "Auto promote PF_INET sockets into PF_INET6 sockets, with IPv4 API emulation.");
+#endif
+
static struct ctl_table ipv6_table_template[] = {
{
.procname = "bindv6only",
@@ -73,6 +88,17 @@ static struct ctl_table ipv6_rotable[] = {
.proc_handler = proc_dointvec_minmax,
.extra1 = &one
},
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ {
+ .procname = "ipv4_emulation",
+ .data = &sysctl_ipv4_emulation,
+ .maxlen = sizeof(bool),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
+#endif
{ }
};
diff --git a/net/socket.c b/net/socket.c
index fe20c319a0bb..e7d2f5281ff3 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -101,6 +101,7 @@
#include <linux/netfilter.h>
#include <linux/if_tun.h>
+#include <linux/ipv6.h>
#include <linux/ipv6_route.h>
#include <linux/route.h>
#include <linux/sockios.h>
@@ -178,30 +179,171 @@ static DEFINE_PER_CPU(int, sockets_in_use);
* divide and look after the messy bits.
*/
+static int ipv6_promote_ipv4_address(struct sock *sk,
+ struct sockaddr_storage * kaddr, int * addr_len)
+{
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ if (!sk) {
+ pr_warning("ipv6_promote_ipv4_address: no sk\n");
+ return 0;
+ }
+
+ if (sk->sk_family != PF_INET6) {
+ //pr_warning("ipv6_promote_ipv4_address: sk_family == %d\n", sk->sk_family);
+ return 0;
+ }
+
+ if (!inet6_sk(sk)->ipv4emu) {
+ //pr_warning("ipv6_promote_ipv4_address: not ipv4emu\n");
+ return 0;
+ }
+
+ if (kaddr->ss_family == AF_UNSPEC) {
+ //pr_warning("ipv6_promote_ipv4_address: unspec\n");
+ return 0;
+ }
+
+ if (kaddr->ss_family != AF_INET) {
+ pr_warning("ipv6_promote_ipv4_address: addr is %d\n", kaddr->ss_family);
+ return -EAFNOSUPPORT;
+ }
+
+ if (*addr_len < sizeof(struct sockaddr_in)) {
+ pr_warning("ipv6_promote_ipv4_address: addr_len == %d\n", *addr_len);
+ return -EINVAL;
+ }
+
+ {
+ const struct sockaddr_in * kaddr4 = (const struct sockaddr_in *)kaddr;
+ struct sockaddr_in6 * kaddr6 = (struct sockaddr_in6 *)kaddr;
+ __be16 port = kaddr4->sin_port;
+ __be32 ipv4 = kaddr4->sin_addr.s_addr;
+
+ //*addr_len = sizeof(struct sockaddr_in6);
+ *addr_len = 24; //SIN6_LEN_RFC2133; /* 24 = 2+2+4+16, ie. without scope id */
+// Why not fill in scope_id with 0 ?
+// One way to avoid the magic 24 constant is to use offsetof(struct sockaddr_in6, scope_id)
+ kaddr6->sin6_family = AF_INET6;
+ kaddr6->sin6_port = port;
+ kaddr6->sin6_flowinfo = htonl(0);
+ kaddr6->sin6_addr.s6_addr32[0] = htonl(0);
+ kaddr6->sin6_addr.s6_addr32[1] = htonl(0);
+ kaddr6->sin6_addr.s6_addr32[2] = ntohl(ipv4) ? htonl(0xFFFF) : htonl(0);
+ kaddr6->sin6_addr.s6_addr32[3] = ipv4;
+ kaddr6->sin6_scope_id = 0;
+
+ pr_debug("ipv6_promote_ipv4_address: ok [%08X:%d]\n", ntohl(ipv4), ntohs(port));
+ }
+#endif
+ return 0;
+}
+
+static int ipv6_demote_ipv6_address(struct sock *sk, struct sockaddr_storage * kaddr, int * addr_len) {
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ if (!sk) {
+ pr_warning("ipv6_demote_ipv6_address: no sk\n");
+ return 0;
+ }
+
+ if (sk->sk_family != PF_INET6) {
+ //pr_warning("ipv6_demote_ipv6_address: sk_family == %d\n", sk->sk_family);
+ return 0;
+ }
+
+ if (!inet6_sk(sk)->ipv4emu) {
+ //pr_warning("ipv6_demote_ipv6_address: not ipv4emu\n");
+ return 0;
+ }
+
+ if (kaddr->ss_family != AF_INET6) {
+ pr_warning("ipv6_demote_ipv6_address: addr is %d\n", kaddr->ss_family);
+ return -EAFNOSUPPORT;
+ }
+
+ if (*addr_len < sizeof(struct sockaddr_in6)) {
+ pr_warning("ipv6_demote_ipv6_address: addr_len == %d\n", *addr_len);
+ return -EINVAL;
+ }
+
+ {
+ struct sockaddr_in6 const * kaddr6 = (struct sockaddr_in6 const *)kaddr;
+ struct sockaddr_in * kaddr4 = (struct sockaddr_in *)kaddr;
+ __be16 port = kaddr6->sin6_port;
+ __be32 ipv6a = kaddr6->sin6_addr.s6_addr32[0];
+ __be32 ipv6b = kaddr6->sin6_addr.s6_addr32[1];
+ __be32 ipv6c = kaddr6->sin6_addr.s6_addr32[2];
+ __be32 ipv4 = kaddr6->sin6_addr.s6_addr32[3];
+
+// please use ipv6_addr_v4mapped()
+
+ if (ipv6a) {
+ pr_warning("ipv6_demote_ipv6_address: not mapped [1]\n");
+ return -EINVAL;
+ }
+
+ if (ipv6b) {
+ pr_warning("ipv6_demote_ipv6_address: not mapped [2]\n");
+ return -EINVAL;
+ }
+
+ if ((ipv6c != htonl(0)) && (ipv6c != htonl(0xFFFF))) {
+ pr_warning("ipv6_demote_ipv6_address: not mapped [3]\n");
+ return -EINVAL;
+ }
+
+ if ((ipv6c == htonl(0)) && (ipv4 != htonl(0))) {
+ pr_warning("ipv6_demote_ipv6_address: not mapped [4]\n");
+ return -EINVAL;
+ }
+
+// Really avoid those magic values...
+// Since I doubt this is performance critical, just do the whole struct clear at the beginning:
+// memset(uaddr4, 0, sizeof(*uaddr4));
+
+ *addr_len = sizeof(struct sockaddr_in); // 2 + 2 + 4 + 8 padding
+ kaddr4->sin_family = AF_INET;
+ kaddr4->sin_port = port;
+ kaddr4->sin_addr.s_addr = ipv4;
+ memset(kaddr4->sin_zero, 0, 8);
+
+ pr_debug("ipv6_demote_ipv6_address: ok [%08X:%d]\n", ntohl(ipv4), ntohs(port));
+ }
+#endif
+ return 0;
+}
+
/**
* move_addr_to_kernel - copy a socket address into kernel space
+ * @sk: socket which is receiving the address (or NULL)
* @uaddr: Address in user space
* @kaddr: Address in kernel space
- * @ulen: Length in user space
+ * @ulen: pointer to user space length
*
* The address is copied into kernel space. If the provided address is
* too long an error code of -EINVAL is returned. If the copy gives
* invalid addresses -EFAULT is returned. On a success 0 is returned.
*/
-int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *kaddr)
+int move_addr_to_kernel(struct sock *sk, void __user *uaddr, int *ulen,
+ struct sockaddr_storage *kaddr)
{
- if (ulen < 0 || ulen > sizeof(struct sockaddr_storage))
+ int err;
+
+ if (*ulen < 0 || *ulen > sizeof(struct sockaddr_storage))
return -EINVAL;
- if (ulen == 0)
+ if (*ulen == 0)
return 0;
- if (copy_from_user(kaddr, uaddr, ulen))
+ if (copy_from_user(kaddr, uaddr, *ulen))
return -EFAULT;
- return audit_sockaddr(ulen, kaddr);
+ err = audit_sockaddr(*ulen, kaddr);
+ if (err)
+ return err;
+ return ipv6_promote_ipv4_address(sk, kaddr, ulen);
}
/**
* move_addr_to_user - copy an address to user space
+ * @sk: socket which is generating the address (or NULL)
* @kaddr: kernel space address
* @klen: length of address in kernel
* @uaddr: user space address
@@ -217,7 +359,7 @@ int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *k
* specified. Zero is returned for a success.
*/
-static int move_addr_to_user(struct sockaddr_storage *kaddr, int klen,
+static int move_addr_to_user(struct sock *sk, struct sockaddr_storage *kaddr, int klen,
void __user *uaddr, int __user *ulen)
{
int err;
@@ -225,6 +367,9 @@ static int move_addr_to_user(struct sockaddr_storage *kaddr, int klen,
BUG_ON(klen > sizeof(struct sockaddr_storage));
err = get_user(len, ulen);
+ if (err)
+ return err;
+ err = ipv6_demote_ipv6_address(sk, kaddr, &klen);
if (err)
return err;
if (len > klen)
@@ -1249,12 +1394,19 @@ call_kill:
}
EXPORT_SYMBOL(sock_wake_async);
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+extern bool sysctl_ipv4_emulation;
+#endif
+
int __sock_create(struct net *net, int family, int type, int protocol,
struct socket **res, int kern)
{
int err;
struct socket *sock;
const struct net_proto_family *pf;
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ bool ipv4emu = false;
+#endif
/*
* Check protocol is in range
@@ -1283,6 +1435,13 @@ int __sock_create(struct net *net, int family, int type, int protocol,
if (err)
return err;
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ if (sysctl_ipv4_emulation && !kern && family == PF_INET) {
+ family = PF_INET6;
+ ipv4emu = true;
+ }
+#endif
+
/*
* Allocate the socket and allow the family to set things up. if
* the protocol is 0, the family is instructed to select an appropriate
@@ -1328,6 +1487,14 @@ int __sock_create(struct net *net, int family, int type, int protocol,
if (err < 0)
goto out_module_put;
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ if (ipv4emu) {
+ inet6_sk(sock->sk)->ipv4emu = 1;
+ /* we need to clear ipv6only, since it could have defaulted to true via sysctl */
+ sock->sk->sk_ipv6only = 0;
+ }
+#endif
+
/*
* Now to bump the refcnt of the [loadable] module that owns this
* socket at sock_release time we decrement its refcnt.
@@ -1532,7 +1699,7 @@ SYSCALL_DEFINE3(bind, int, fd, struct sockaddr __user *, umyaddr, int, addrlen)
sock = sockfd_lookup_light(fd, &err, &fput_needed);
if (sock) {
- err = move_addr_to_kernel(umyaddr, addrlen, &address);
+ err = move_addr_to_kernel(sock->sk, umyaddr, &addrlen, &address);
if (err >= 0) {
err = security_socket_bind(sock,
(struct sockaddr *)&address,
@@ -1646,7 +1813,7 @@ SYSCALL_DEFINE4(accept4, int, fd, struct sockaddr __user *, upeer_sockaddr,
err = -ECONNABORTED;
goto out_fd;
}
- err = move_addr_to_user(&address,
+ err = move_addr_to_user(newsock->sk, &address,
len, upeer_sockaddr, upeer_addrlen);
if (err < 0)
goto out_fd;
@@ -1695,7 +1862,7 @@ SYSCALL_DEFINE3(connect, int, fd, struct sockaddr __user *, uservaddr,
sock = sockfd_lookup_light(fd, &err, &fput_needed);
if (!sock)
goto out;
- err = move_addr_to_kernel(uservaddr, addrlen, &address);
+ err = move_addr_to_kernel(sock->sk, uservaddr, &addrlen, &address);
if (err < 0)
goto out_put;
@@ -1735,7 +1902,7 @@ SYSCALL_DEFINE3(getsockname, int, fd, struct sockaddr __user *, usockaddr,
err = sock->ops->getname(sock, (struct sockaddr *)&address, &len, 0);
if (err)
goto out_put;
- err = move_addr_to_user(&address, len, usockaddr, usockaddr_len);
+ err = move_addr_to_user(sock->sk, &address, len, usockaddr, usockaddr_len);
out_put:
fput_light(sock->file, fput_needed);
@@ -1767,7 +1934,7 @@ SYSCALL_DEFINE3(getpeername, int, fd, struct sockaddr __user *, usockaddr,
sock->ops->getname(sock, (struct sockaddr *)&address, &len,
1);
if (!err)
- err = move_addr_to_user(&address, len, usockaddr,
+ err = move_addr_to_user(sock->sk, &address, len, usockaddr,
usockaddr_len);
fput_light(sock->file, fput_needed);
}
@@ -1806,7 +1973,7 @@ SYSCALL_DEFINE6(sendto, int, fd, void __user *, buff, size_t, len,
msg.msg_controllen = 0;
msg.msg_namelen = 0;
if (addr) {
- err = move_addr_to_kernel(addr, addr_len, &address);
+ err = move_addr_to_kernel(sock->sk, addr, &addr_len, &address);
if (err < 0)
goto out_put;
msg.msg_name = (struct sockaddr *)&address;
@@ -1871,7 +2038,7 @@ SYSCALL_DEFINE6(recvfrom, int, fd, void __user *, ubuf, size_t, size,
err = sock_recvmsg(sock, &msg, size, flags);
if (err >= 0 && addr != NULL) {
- err2 = move_addr_to_user(&address,
+ err2 = move_addr_to_user(sock->sk, &address,
msg.msg_namelen, addr, addr_len);
if (err2 < 0)
err = err2;
@@ -2042,9 +2209,9 @@ static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
/* This will also move the address data into kernel space */
if (MSG_CMSG_COMPAT & flags) {
- err = verify_compat_iovec(msg_sys, iov, &address, VERIFY_READ);
+ err = verify_compat_iovec(sock->sk, msg_sys, iov, &address, VERIFY_READ);
} else
- err = verify_iovec(msg_sys, iov, &address, VERIFY_READ);
+ err = verify_iovec(sock->sk, msg_sys, iov, &address, VERIFY_READ);
if (err < 0)
goto out_freeiov;
total_len = err;
@@ -2258,9 +2425,9 @@ static int ___sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
uaddr = (__force void __user *)msg_sys->msg_name;
uaddr_len = COMPAT_NAMELEN(msg);
if (MSG_CMSG_COMPAT & flags)
- err = verify_compat_iovec(msg_sys, iov, &addr, VERIFY_WRITE);
+ err = verify_compat_iovec(sock->sk, msg_sys, iov, &addr, VERIFY_WRITE);
else
- err = verify_iovec(msg_sys, iov, &addr, VERIFY_WRITE);
+ err = verify_iovec(sock->sk, msg_sys, iov, &addr, VERIFY_WRITE);
if (err < 0)
goto out_freeiov;
total_len = err;
@@ -2280,7 +2447,7 @@ static int ___sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
len = err;
if (uaddr != NULL) {
- err = move_addr_to_user(&addr,
+ err = move_addr_to_user(sock->sk, &addr,
msg_sys->msg_namelen, uaddr,
uaddr_len);
if (err < 0)
@@ -3159,7 +3326,11 @@ static int routing_ioctl(struct net *net, struct socket *sock,
u32 rtdev;
mm_segment_t old_fs = get_fs();
- if (sock && sock->sk && sock->sk->sk_family == AF_INET6) { /* ipv6 */
+ if (sock && sock->sk && sock->sk->sk_family == AF_INET6
+#if defined(CONFIG_IPV6_IPV4_EMULATE)
+ && !inet6_sk(sock->sk)->ipv4emu
+#endif
+ ) { /* ipv6 */
struct in6_rtmsg32 __user *ur6 = argp;
ret = copy_from_user(&r6.rtmsg_dst, &(ur6->rtmsg_dst),
3 * sizeof(struct in6_addr));
--
2.55.0.795.g602f6c329a-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] [RFC] net-ipv6: ipv4 emulation support
2026-07-13 8:16 [PATCH] [RFC] net-ipv6: ipv4 emulation support Maciej Żenczykowski
@ 2026-07-13 9:05 ` Maciej Żenczykowski
0 siblings, 0 replies; 2+ messages in thread
From: Maciej Żenczykowski @ 2026-07-13 9:05 UTC (permalink / raw)
To: Maciej Żenczykowski
Cc: Linux Network Development Mailing List,
Fernando Fernandez Mancera
Note that this is absolutely ancient - it's a patch from March 2012
against 3.18 ;-)
But maybe something like this could be pursued?
From what I (vaguely) remember I was able to boot my linux workstation
to a working GUI with this.
On Mon, Jul 13, 2026 at 10:16 AM Maciej Żenczykowski <maze@google.com> wrote:
>
> Change-Id: Ibab1a59f4730f3fd0a7d14fffc5100a02a170ac6
> ---
> gconfigs/Gconfig.net-configs.ipv6 | 2 +
> include/linux/ipv6.h | 6 +-
> include/linux/socket.h | 5 +-
> include/net/compat.h | 2 +-
> net/compat.c | 6 +-
> net/core/iovec.c | 4 +-
> net/ipv6/Kconfig | 19 +++
> net/ipv6/af_inet6.c | 5 +
> net/ipv6/ipv6_sockglue.c | 8 +-
> net/ipv6/sysctl_net_ipv6.c | 26 ++++
> net/socket.c | 211 +++++++++++++++++++++++++++---
> 11 files changed, 260 insertions(+), 34 deletions(-)
> create mode 100644 gconfigs/Gconfig.net-configs.ipv6
>
> diff --git a/gconfigs/Gconfig.net-configs.ipv6 b/gconfigs/Gconfig.net-configs.ipv6
> new file mode 100644
> index 000000000000..9eb5694bae8e
> --- /dev/null
> +++ b/gconfigs/Gconfig.net-configs.ipv6
> @@ -0,0 +1,2 @@
> +CONFIG_IPV6_IPV4_EMULATE=y
> +CONFIG_IPV6_IPV4_EMULATE_SYSCTL_DEFAULT=y
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index ff560537dd61..8bc5306094b5 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -157,11 +157,13 @@ struct ipv6_pinfo {
> #if defined(__BIG_ENDIAN_BITFIELD)
> /* Packed in 16bits. */
> __s16 mcast_hops:9;
> - __u16 __unused_2:6,
> + __u16 __unused_2:5,
> + ipv4emu:1,
> mc_loop:1;
> #else
> __u16 mc_loop:1,
> - __unused_2:6;
> + ipv4emu:1,
> + __unused_2:5;
> __s16 mcast_hops:9;
> #endif
> int ucast_oif;
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index bb9b83640070..4ae959a3443b 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -8,6 +8,7 @@
> #include <linux/types.h> /* pid_t */
> #include <linux/compiler.h> /* __user */
> #include <uapi/linux/socket.h>
> +struct sock; /* from net/sock.h */
>
> struct pid;
> struct cred;
> @@ -312,8 +313,8 @@ extern int csum_partial_copy_fromiovecend(unsigned char *kdata,
> extern unsigned long iov_pages(const struct iovec *iov, int offset,
> unsigned long nr_segs);
>
> -extern int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode);
> -extern int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *kaddr);
> +extern int verify_iovec(struct sock *sk, struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode);
> +extern int move_addr_to_kernel(struct sock *sk, void __user *uaddr, int *ulen, struct sockaddr_storage *kaddr);
> extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data);
>
> struct timespec;
> diff --git a/include/net/compat.h b/include/net/compat.h
> index 3b603b199c01..b9ee7aa5a31f 100644
> --- a/include/net/compat.h
> +++ b/include/net/compat.h
> @@ -41,7 +41,7 @@ int compat_sock_get_timestampns(struct sock *, struct timespec __user *);
> #endif /* defined(CONFIG_COMPAT) */
>
> int get_compat_msghdr(struct msghdr *, struct compat_msghdr __user *);
> -int verify_compat_iovec(struct msghdr *, struct iovec *,
> +int verify_compat_iovec(struct sock *, struct msghdr *, struct iovec *,
> struct sockaddr_storage *, int);
> asmlinkage long compat_sys_sendmsg(int, struct compat_msghdr __user *,
> unsigned int);
> diff --git a/net/compat.c b/net/compat.c
> index bc8aeefddf3f..f66bd6552204 100644
> --- a/net/compat.c
> +++ b/net/compat.c
> @@ -80,15 +80,15 @@ int get_compat_msghdr(struct msghdr *kmsg, struct compat_msghdr __user *umsg)
> }
>
> /* I've named the args so it is easy to tell whose space the pointers are in. */
> -int verify_compat_iovec(struct msghdr *kern_msg, struct iovec *kern_iov,
> +int verify_compat_iovec(struct sock *sk, struct msghdr *kern_msg, struct iovec *kern_iov,
> struct sockaddr_storage *kern_address, int mode)
> {
> int tot_len;
>
> if (kern_msg->msg_name && kern_msg->msg_namelen) {
> if (mode == VERIFY_READ) {
> - int err = move_addr_to_kernel(kern_msg->msg_name,
> - kern_msg->msg_namelen,
> + int err = move_addr_to_kernel(sk, kern_msg->msg_name,
> + &kern_msg->msg_namelen,
> kern_address);
> if (err < 0)
> return err;
> diff --git a/net/core/iovec.c b/net/core/iovec.c
> index e1ec45ab1e63..a7a393cae2a7 100644
> --- a/net/core/iovec.c
> +++ b/net/core/iovec.c
> @@ -35,7 +35,7 @@
> * in any case.
> */
>
> -int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode)
> +int verify_iovec(struct sock *sk, struct msghdr *m, struct iovec *iov, struct sockaddr_storage *address, int mode)
> {
> int size, ct, err;
>
> @@ -43,7 +43,7 @@ int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr_storage *a
> if (mode == VERIFY_READ) {
> void __user *namep;
> namep = (void __user __force *) m->msg_name;
> - err = move_addr_to_kernel(namep, m->msg_namelen,
> + err = move_addr_to_kernel(sk, namep, &m->msg_namelen,
> address);
> if (err < 0)
> return err;
> diff --git a/net/ipv6/Kconfig b/net/ipv6/Kconfig
> index 438a73aa777c..69924a6c2257 100644
> --- a/net/ipv6/Kconfig
> +++ b/net/ipv6/Kconfig
> @@ -21,6 +21,25 @@ menuconfig IPV6
>
> if IPV6
>
> +config IPV6_IPV4_EMULATE
> + bool "IPv6: IPv4 socket interface emulation support"
> + default n
> + depends on IPV6=y
> + ---help---
> + Whether to include support code which allows using a kernel IPv6
> + socket from userspace as if it was an IPv4 socket.
> +
> + ie. this is a userspace-kernel IP address translation shim layer.
> +
> +config IPV6_IPV4_EMULATE_SYSCTL_DEFAULT
> + bool "IPv6: IPv4 socket emulation - default sysctl setting"
> + default n
> + depends on IPV6_IPV4_EMULATE
> + ---help---
> + Default value for /proc/sys/net/ipv6/ipv4_emulation
> + The content of this sysctl file determines whether userspace asking
> + for IPv4 sockets gets IPv6 sockets with IPv4 emulation turned on.
> +
> config IPV6_ROUTER_PREF
> bool "IPv6: Router Preference (RFC 4191) support"
> ---help---
> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index e8c4400f23e9..4f08abdf06e0 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -476,6 +476,11 @@ int inet6_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
> struct sock *sk = sock->sk;
> struct net *net = sock_net(sk);
>
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + if (inet6_sk(sk)->ipv4emu)
> + return inet_ioctl(sock, cmd, arg);
> +#endif
> +
> switch (cmd) {
> case SIOCGSTAMP:
> return sock_get_timestamp(sk, (struct timeval __user *)arg);
> diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> index e1a9583bb419..2e97c6d55b62 100644
> --- a/net/ipv6/ipv6_sockglue.c
> +++ b/net/ipv6/ipv6_sockglue.c
> @@ -857,7 +857,7 @@ int ipv6_setsockopt(struct sock *sk, int level, int optname,
> if (level == SOL_IP && sk->sk_type != SOCK_RAW)
> return udp_prot.setsockopt(sk, level, optname, optval, optlen);
>
> - if (level != SOL_IPV6)
> + if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
> return -ENOPROTOOPT;
>
> err = do_ipv6_setsockopt(sk, level, optname, optval, optlen);
> @@ -888,7 +888,7 @@ int compat_ipv6_setsockopt(struct sock *sk, int level, int optname,
> return udp_prot.setsockopt(sk, level, optname, optval, optlen);
> }
>
> - if (level != SOL_IPV6)
> + if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
> return -ENOPROTOOPT;
>
> if (optname >= MCAST_JOIN_GROUP && optname <= MCAST_MSFILTER)
> @@ -1297,7 +1297,7 @@ int ipv6_getsockopt(struct sock *sk, int level, int optname,
> if (level == SOL_IP && sk->sk_type != SOCK_RAW)
> return udp_prot.getsockopt(sk, level, optname, optval, optlen);
>
> - if (level != SOL_IPV6)
> + if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
> return -ENOPROTOOPT;
>
> err = do_ipv6_getsockopt(sk, level, optname, optval, optlen, 0);
> @@ -1334,7 +1334,7 @@ int compat_ipv6_getsockopt(struct sock *sk, int level, int optname,
> return udp_prot.getsockopt(sk, level, optname, optval, optlen);
> }
>
> - if (level != SOL_IPV6)
> + if ((level != SOL_IPV6) || (inet6_sk(sk)->ipv4emu))
> return -ENOPROTOOPT;
>
> if (optname == MCAST_MSFILTER)
> diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
> index c5c10fafcfe2..0ab6a8d5aa57 100644
> --- a/net/ipv6/sysctl_net_ipv6.c
> +++ b/net/ipv6/sysctl_net_ipv6.c
> @@ -6,6 +6,7 @@
> */
>
> #include <linux/mm.h>
> +#include <linux/module.h>
> #include <linux/sysctl.h>
> #include <linux/in6.h>
> #include <linux/ipv6.h>
> @@ -18,6 +19,20 @@
>
> static int one = 1;
>
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> +static int zero;
> +
> +# if defined(CONFIG_IPV6_IPV4_EMULATE_SYSCTL_DEFAULT)
> +bool sysctl_ipv4_emulation = true;
> +# else
> +bool sysctl_ipv4_emulation = false;
> +# endif
> +
> +module_param_named(ipv4_emulation, sysctl_ipv4_emulation, bool, S_IRUGO|S_IWUSR);
> +MODULE_PARM_DESC(ipv4_emulation,
> + "Auto promote PF_INET sockets into PF_INET6 sockets, with IPv4 API emulation.");
> +#endif
> +
> static struct ctl_table ipv6_table_template[] = {
> {
> .procname = "bindv6only",
> @@ -73,6 +88,17 @@ static struct ctl_table ipv6_rotable[] = {
> .proc_handler = proc_dointvec_minmax,
> .extra1 = &one
> },
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + {
> + .procname = "ipv4_emulation",
> + .data = &sysctl_ipv4_emulation,
> + .maxlen = sizeof(bool),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = &zero,
> + .extra2 = &one,
> + },
> +#endif
> { }
> };
>
> diff --git a/net/socket.c b/net/socket.c
> index fe20c319a0bb..e7d2f5281ff3 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -101,6 +101,7 @@
> #include <linux/netfilter.h>
>
> #include <linux/if_tun.h>
> +#include <linux/ipv6.h>
> #include <linux/ipv6_route.h>
> #include <linux/route.h>
> #include <linux/sockios.h>
> @@ -178,30 +179,171 @@ static DEFINE_PER_CPU(int, sockets_in_use);
> * divide and look after the messy bits.
> */
>
> +static int ipv6_promote_ipv4_address(struct sock *sk,
> + struct sockaddr_storage * kaddr, int * addr_len)
> +{
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + if (!sk) {
> + pr_warning("ipv6_promote_ipv4_address: no sk\n");
> + return 0;
> + }
> +
> + if (sk->sk_family != PF_INET6) {
> + //pr_warning("ipv6_promote_ipv4_address: sk_family == %d\n", sk->sk_family);
> + return 0;
> + }
> +
> + if (!inet6_sk(sk)->ipv4emu) {
> + //pr_warning("ipv6_promote_ipv4_address: not ipv4emu\n");
> + return 0;
> + }
> +
> + if (kaddr->ss_family == AF_UNSPEC) {
> + //pr_warning("ipv6_promote_ipv4_address: unspec\n");
> + return 0;
> + }
> +
> + if (kaddr->ss_family != AF_INET) {
> + pr_warning("ipv6_promote_ipv4_address: addr is %d\n", kaddr->ss_family);
> + return -EAFNOSUPPORT;
> + }
> +
> + if (*addr_len < sizeof(struct sockaddr_in)) {
> + pr_warning("ipv6_promote_ipv4_address: addr_len == %d\n", *addr_len);
> + return -EINVAL;
> + }
> +
> + {
> + const struct sockaddr_in * kaddr4 = (const struct sockaddr_in *)kaddr;
> + struct sockaddr_in6 * kaddr6 = (struct sockaddr_in6 *)kaddr;
> + __be16 port = kaddr4->sin_port;
> + __be32 ipv4 = kaddr4->sin_addr.s_addr;
> +
> + //*addr_len = sizeof(struct sockaddr_in6);
> + *addr_len = 24; //SIN6_LEN_RFC2133; /* 24 = 2+2+4+16, ie. without scope id */
> +// Why not fill in scope_id with 0 ?
> +// One way to avoid the magic 24 constant is to use offsetof(struct sockaddr_in6, scope_id)
> + kaddr6->sin6_family = AF_INET6;
> + kaddr6->sin6_port = port;
> + kaddr6->sin6_flowinfo = htonl(0);
> + kaddr6->sin6_addr.s6_addr32[0] = htonl(0);
> + kaddr6->sin6_addr.s6_addr32[1] = htonl(0);
> + kaddr6->sin6_addr.s6_addr32[2] = ntohl(ipv4) ? htonl(0xFFFF) : htonl(0);
> + kaddr6->sin6_addr.s6_addr32[3] = ipv4;
> + kaddr6->sin6_scope_id = 0;
> +
> + pr_debug("ipv6_promote_ipv4_address: ok [%08X:%d]\n", ntohl(ipv4), ntohs(port));
> + }
> +#endif
> + return 0;
> +}
> +
> +static int ipv6_demote_ipv6_address(struct sock *sk, struct sockaddr_storage * kaddr, int * addr_len) {
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + if (!sk) {
> + pr_warning("ipv6_demote_ipv6_address: no sk\n");
> + return 0;
> + }
> +
> + if (sk->sk_family != PF_INET6) {
> + //pr_warning("ipv6_demote_ipv6_address: sk_family == %d\n", sk->sk_family);
> + return 0;
> + }
> +
> + if (!inet6_sk(sk)->ipv4emu) {
> + //pr_warning("ipv6_demote_ipv6_address: not ipv4emu\n");
> + return 0;
> + }
> +
> + if (kaddr->ss_family != AF_INET6) {
> + pr_warning("ipv6_demote_ipv6_address: addr is %d\n", kaddr->ss_family);
> + return -EAFNOSUPPORT;
> + }
> +
> + if (*addr_len < sizeof(struct sockaddr_in6)) {
> + pr_warning("ipv6_demote_ipv6_address: addr_len == %d\n", *addr_len);
> + return -EINVAL;
> + }
> +
> + {
> + struct sockaddr_in6 const * kaddr6 = (struct sockaddr_in6 const *)kaddr;
> + struct sockaddr_in * kaddr4 = (struct sockaddr_in *)kaddr;
> + __be16 port = kaddr6->sin6_port;
> + __be32 ipv6a = kaddr6->sin6_addr.s6_addr32[0];
> + __be32 ipv6b = kaddr6->sin6_addr.s6_addr32[1];
> + __be32 ipv6c = kaddr6->sin6_addr.s6_addr32[2];
> + __be32 ipv4 = kaddr6->sin6_addr.s6_addr32[3];
> +
> +// please use ipv6_addr_v4mapped()
> +
> + if (ipv6a) {
> + pr_warning("ipv6_demote_ipv6_address: not mapped [1]\n");
> + return -EINVAL;
> + }
> +
> + if (ipv6b) {
> + pr_warning("ipv6_demote_ipv6_address: not mapped [2]\n");
> + return -EINVAL;
> + }
> +
> + if ((ipv6c != htonl(0)) && (ipv6c != htonl(0xFFFF))) {
> + pr_warning("ipv6_demote_ipv6_address: not mapped [3]\n");
> + return -EINVAL;
> + }
> +
> + if ((ipv6c == htonl(0)) && (ipv4 != htonl(0))) {
> + pr_warning("ipv6_demote_ipv6_address: not mapped [4]\n");
> + return -EINVAL;
> + }
> +
> +// Really avoid those magic values...
> +// Since I doubt this is performance critical, just do the whole struct clear at the beginning:
> +// memset(uaddr4, 0, sizeof(*uaddr4));
> +
> + *addr_len = sizeof(struct sockaddr_in); // 2 + 2 + 4 + 8 padding
> + kaddr4->sin_family = AF_INET;
> + kaddr4->sin_port = port;
> + kaddr4->sin_addr.s_addr = ipv4;
> + memset(kaddr4->sin_zero, 0, 8);
> +
> + pr_debug("ipv6_demote_ipv6_address: ok [%08X:%d]\n", ntohl(ipv4), ntohs(port));
> + }
> +#endif
> + return 0;
> +}
> +
> /**
> * move_addr_to_kernel - copy a socket address into kernel space
> + * @sk: socket which is receiving the address (or NULL)
> * @uaddr: Address in user space
> * @kaddr: Address in kernel space
> - * @ulen: Length in user space
> + * @ulen: pointer to user space length
> *
> * The address is copied into kernel space. If the provided address is
> * too long an error code of -EINVAL is returned. If the copy gives
> * invalid addresses -EFAULT is returned. On a success 0 is returned.
> */
>
> -int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *kaddr)
> +int move_addr_to_kernel(struct sock *sk, void __user *uaddr, int *ulen,
> + struct sockaddr_storage *kaddr)
> {
> - if (ulen < 0 || ulen > sizeof(struct sockaddr_storage))
> + int err;
> +
> + if (*ulen < 0 || *ulen > sizeof(struct sockaddr_storage))
> return -EINVAL;
> - if (ulen == 0)
> + if (*ulen == 0)
> return 0;
> - if (copy_from_user(kaddr, uaddr, ulen))
> + if (copy_from_user(kaddr, uaddr, *ulen))
> return -EFAULT;
> - return audit_sockaddr(ulen, kaddr);
> + err = audit_sockaddr(*ulen, kaddr);
> + if (err)
> + return err;
> + return ipv6_promote_ipv4_address(sk, kaddr, ulen);
> }
>
> /**
> * move_addr_to_user - copy an address to user space
> + * @sk: socket which is generating the address (or NULL)
> * @kaddr: kernel space address
> * @klen: length of address in kernel
> * @uaddr: user space address
> @@ -217,7 +359,7 @@ int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr_storage *k
> * specified. Zero is returned for a success.
> */
>
> -static int move_addr_to_user(struct sockaddr_storage *kaddr, int klen,
> +static int move_addr_to_user(struct sock *sk, struct sockaddr_storage *kaddr, int klen,
> void __user *uaddr, int __user *ulen)
> {
> int err;
> @@ -225,6 +367,9 @@ static int move_addr_to_user(struct sockaddr_storage *kaddr, int klen,
>
> BUG_ON(klen > sizeof(struct sockaddr_storage));
> err = get_user(len, ulen);
> + if (err)
> + return err;
> + err = ipv6_demote_ipv6_address(sk, kaddr, &klen);
> if (err)
> return err;
> if (len > klen)
> @@ -1249,12 +1394,19 @@ call_kill:
> }
> EXPORT_SYMBOL(sock_wake_async);
>
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> +extern bool sysctl_ipv4_emulation;
> +#endif
> +
> int __sock_create(struct net *net, int family, int type, int protocol,
> struct socket **res, int kern)
> {
> int err;
> struct socket *sock;
> const struct net_proto_family *pf;
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + bool ipv4emu = false;
> +#endif
>
> /*
> * Check protocol is in range
> @@ -1283,6 +1435,13 @@ int __sock_create(struct net *net, int family, int type, int protocol,
> if (err)
> return err;
>
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + if (sysctl_ipv4_emulation && !kern && family == PF_INET) {
> + family = PF_INET6;
> + ipv4emu = true;
> + }
> +#endif
> +
> /*
> * Allocate the socket and allow the family to set things up. if
> * the protocol is 0, the family is instructed to select an appropriate
> @@ -1328,6 +1487,14 @@ int __sock_create(struct net *net, int family, int type, int protocol,
> if (err < 0)
> goto out_module_put;
>
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + if (ipv4emu) {
> + inet6_sk(sock->sk)->ipv4emu = 1;
> + /* we need to clear ipv6only, since it could have defaulted to true via sysctl */
> + sock->sk->sk_ipv6only = 0;
> + }
> +#endif
> +
> /*
> * Now to bump the refcnt of the [loadable] module that owns this
> * socket at sock_release time we decrement its refcnt.
> @@ -1532,7 +1699,7 @@ SYSCALL_DEFINE3(bind, int, fd, struct sockaddr __user *, umyaddr, int, addrlen)
>
> sock = sockfd_lookup_light(fd, &err, &fput_needed);
> if (sock) {
> - err = move_addr_to_kernel(umyaddr, addrlen, &address);
> + err = move_addr_to_kernel(sock->sk, umyaddr, &addrlen, &address);
> if (err >= 0) {
> err = security_socket_bind(sock,
> (struct sockaddr *)&address,
> @@ -1646,7 +1813,7 @@ SYSCALL_DEFINE4(accept4, int, fd, struct sockaddr __user *, upeer_sockaddr,
> err = -ECONNABORTED;
> goto out_fd;
> }
> - err = move_addr_to_user(&address,
> + err = move_addr_to_user(newsock->sk, &address,
> len, upeer_sockaddr, upeer_addrlen);
> if (err < 0)
> goto out_fd;
> @@ -1695,7 +1862,7 @@ SYSCALL_DEFINE3(connect, int, fd, struct sockaddr __user *, uservaddr,
> sock = sockfd_lookup_light(fd, &err, &fput_needed);
> if (!sock)
> goto out;
> - err = move_addr_to_kernel(uservaddr, addrlen, &address);
> + err = move_addr_to_kernel(sock->sk, uservaddr, &addrlen, &address);
> if (err < 0)
> goto out_put;
>
> @@ -1735,7 +1902,7 @@ SYSCALL_DEFINE3(getsockname, int, fd, struct sockaddr __user *, usockaddr,
> err = sock->ops->getname(sock, (struct sockaddr *)&address, &len, 0);
> if (err)
> goto out_put;
> - err = move_addr_to_user(&address, len, usockaddr, usockaddr_len);
> + err = move_addr_to_user(sock->sk, &address, len, usockaddr, usockaddr_len);
>
> out_put:
> fput_light(sock->file, fput_needed);
> @@ -1767,7 +1934,7 @@ SYSCALL_DEFINE3(getpeername, int, fd, struct sockaddr __user *, usockaddr,
> sock->ops->getname(sock, (struct sockaddr *)&address, &len,
> 1);
> if (!err)
> - err = move_addr_to_user(&address, len, usockaddr,
> + err = move_addr_to_user(sock->sk, &address, len, usockaddr,
> usockaddr_len);
> fput_light(sock->file, fput_needed);
> }
> @@ -1806,7 +1973,7 @@ SYSCALL_DEFINE6(sendto, int, fd, void __user *, buff, size_t, len,
> msg.msg_controllen = 0;
> msg.msg_namelen = 0;
> if (addr) {
> - err = move_addr_to_kernel(addr, addr_len, &address);
> + err = move_addr_to_kernel(sock->sk, addr, &addr_len, &address);
> if (err < 0)
> goto out_put;
> msg.msg_name = (struct sockaddr *)&address;
> @@ -1871,7 +2038,7 @@ SYSCALL_DEFINE6(recvfrom, int, fd, void __user *, ubuf, size_t, size,
> err = sock_recvmsg(sock, &msg, size, flags);
>
> if (err >= 0 && addr != NULL) {
> - err2 = move_addr_to_user(&address,
> + err2 = move_addr_to_user(sock->sk, &address,
> msg.msg_namelen, addr, addr_len);
> if (err2 < 0)
> err = err2;
> @@ -2042,9 +2209,9 @@ static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
>
> /* This will also move the address data into kernel space */
> if (MSG_CMSG_COMPAT & flags) {
> - err = verify_compat_iovec(msg_sys, iov, &address, VERIFY_READ);
> + err = verify_compat_iovec(sock->sk, msg_sys, iov, &address, VERIFY_READ);
> } else
> - err = verify_iovec(msg_sys, iov, &address, VERIFY_READ);
> + err = verify_iovec(sock->sk, msg_sys, iov, &address, VERIFY_READ);
> if (err < 0)
> goto out_freeiov;
> total_len = err;
> @@ -2258,9 +2425,9 @@ static int ___sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
> uaddr = (__force void __user *)msg_sys->msg_name;
> uaddr_len = COMPAT_NAMELEN(msg);
> if (MSG_CMSG_COMPAT & flags)
> - err = verify_compat_iovec(msg_sys, iov, &addr, VERIFY_WRITE);
> + err = verify_compat_iovec(sock->sk, msg_sys, iov, &addr, VERIFY_WRITE);
> else
> - err = verify_iovec(msg_sys, iov, &addr, VERIFY_WRITE);
> + err = verify_iovec(sock->sk, msg_sys, iov, &addr, VERIFY_WRITE);
> if (err < 0)
> goto out_freeiov;
> total_len = err;
> @@ -2280,7 +2447,7 @@ static int ___sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
> len = err;
>
> if (uaddr != NULL) {
> - err = move_addr_to_user(&addr,
> + err = move_addr_to_user(sock->sk, &addr,
> msg_sys->msg_namelen, uaddr,
> uaddr_len);
> if (err < 0)
> @@ -3159,7 +3326,11 @@ static int routing_ioctl(struct net *net, struct socket *sock,
> u32 rtdev;
> mm_segment_t old_fs = get_fs();
>
> - if (sock && sock->sk && sock->sk->sk_family == AF_INET6) { /* ipv6 */
> + if (sock && sock->sk && sock->sk->sk_family == AF_INET6
> +#if defined(CONFIG_IPV6_IPV4_EMULATE)
> + && !inet6_sk(sock->sk)->ipv4emu
> +#endif
> + ) { /* ipv6 */
> struct in6_rtmsg32 __user *ur6 = argp;
> ret = copy_from_user(&r6.rtmsg_dst, &(ur6->rtmsg_dst),
> 3 * sizeof(struct in6_addr));
> --
> 2.55.0.795.g602f6c329a-goog
>
--
Maciej Żenczykowski, Kernel Networking Developer @ Google
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2026-07-13 8:16 [PATCH] [RFC] net-ipv6: ipv4 emulation support Maciej Żenczykowski
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