tun: Extract the vnet handling code

The vnet handling code will be reused by tap.

Functions are renamed to ensure that their names contain "vnet" to
clarify that they are part of the decoupled vnet handling code.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250207-tun-v6-5-fb49cf8b103e@daynix.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 188 insertions, 179 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 873aa2cce4d7..67665d9dd536 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24152,7 +24152,7 @@ W:	http://vtun.sourceforge.net/tun
 F:	Documentation/networking/tuntap.rst
 F:	arch/um/os-Linux/drivers/
 F:	drivers/net/tap.c
-F:	drivers/net/tun.c
+F:	drivers/net/tun*
 
 TURBOCHANNEL SUBSYSTEM
 M:	"Maciej W. Rozycki" <macro@orcam.me.uk>
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index ed79a691eee0..d8f4d3e996a7 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -83,6 +83,8 @@
 #include <linux/uaccess.h>
 #include <linux/proc_fs.h>
 
+#include "tun_vnet.h"
+
 static void tun_default_link_ksettings(struct net_device *dev,
 				       struct ethtool_link_ksettings *cmd);
 
@@ -94,9 +96,6 @@ static void tun_default_link_ksettings(struct net_device *dev,
  * overload it to mean fasync when stored there.
  */
 #define TUN_FASYNC	IFF_ATTACH_QUEUE
-/* High bits in flags field are unused. */
-#define TUN_VNET_LE     0x80000000
-#define TUN_VNET_BE     0x40000000
 
 #define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
 		      IFF_MULTI_QUEUE | IFF_NAPI | IFF_NAPI_FRAGS)
@@ -298,181 +297,6 @@ static bool tun_napi_frags_enabled(const struct tun_file *tfile)
 	return tfile->napi_frags_enabled;
 }
 
-static inline bool tun_legacy_is_little_endian(unsigned int flags)
-{
-	bool be = IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) &&
-		  (flags & TUN_VNET_BE);
-
-	return !be && virtio_legacy_is_little_endian();
-}
-
-static long tun_get_vnet_be(unsigned int flags, int __user *argp)
-{
-	int be = !!(flags & TUN_VNET_BE);
-
-	if (!IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE))
-		return -EINVAL;
-
-	if (put_user(be, argp))
-		return -EFAULT;
-
-	return 0;
-}
-
-static long tun_set_vnet_be(unsigned int *flags, int __user *argp)
-{
-	int be;
-
-	if (!IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE))
-		return -EINVAL;
-
-	if (get_user(be, argp))
-		return -EFAULT;
-
-	if (be)
-		*flags |= TUN_VNET_BE;
-	else
-		*flags &= ~TUN_VNET_BE;
-
-	return 0;
-}
-
-static inline bool tun_is_little_endian(unsigned int flags)
-{
-	return flags & TUN_VNET_LE || tun_legacy_is_little_endian(flags);
-}
-
-static inline u16 tun16_to_cpu(unsigned int flags, __virtio16 val)
-{
-	return __virtio16_to_cpu(tun_is_little_endian(flags), val);
-}
-
-static inline __virtio16 cpu_to_tun16(unsigned int flags, u16 val)
-{
-	return __cpu_to_virtio16(tun_is_little_endian(flags), val);
-}
-
-static long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags,
-			   unsigned int cmd, int __user *sp)
-{
-	int s;
-
-	switch (cmd) {
-	case TUNGETVNETHDRSZ:
-		s = *vnet_hdr_sz;
-		if (put_user(s, sp))
-			return -EFAULT;
-		return 0;
-
-	case TUNSETVNETHDRSZ:
-		if (get_user(s, sp))
-			return -EFAULT;
-		if (s < (int)sizeof(struct virtio_net_hdr))
-			return -EINVAL;
-
-		*vnet_hdr_sz = s;
-		return 0;
-
-	case TUNGETVNETLE:
-		s = !!(*flags & TUN_VNET_LE);
-		if (put_user(s, sp))
-			return -EFAULT;
-		return 0;
-
-	case TUNSETVNETLE:
-		if (get_user(s, sp))
-			return -EFAULT;
-		if (s)
-			*flags |= TUN_VNET_LE;
-		else
-			*flags &= ~TUN_VNET_LE;
-		return 0;
-
-	case TUNGETVNETBE:
-		return tun_get_vnet_be(*flags, sp);
-
-	case TUNSETVNETBE:
-		return tun_set_vnet_be(flags, sp);
-
-	default:
-		return -EINVAL;
-	}
-}
-
-static int tun_vnet_hdr_get(int sz, unsigned int flags, struct iov_iter *from,
-			    struct virtio_net_hdr *hdr)
-{
-	u16 hdr_len;
-
-	if (iov_iter_count(from) < sz)
-		return -EINVAL;
-
-	if (!copy_from_iter_full(hdr, sizeof(*hdr), from))
-		return -EFAULT;
-
-	hdr_len = tun16_to_cpu(flags, hdr->hdr_len);
-
-	if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
-		hdr_len = max(tun16_to_cpu(flags, hdr->csum_start) + tun16_to_cpu(flags, hdr->csum_offset) + 2, hdr_len);
-		hdr->hdr_len = cpu_to_tun16(flags, hdr_len);
-	}
-
-	if (hdr_len > iov_iter_count(from))
-		return -EINVAL;
-
-	iov_iter_advance(from, sz - sizeof(*hdr));
-
-	return hdr_len;
-}
-
-static int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
-			    const struct virtio_net_hdr *hdr)
-{
-	if (unlikely(iov_iter_count(iter) < sz))
-		return -EINVAL;
-
-	if (unlikely(copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr)))
-		return -EFAULT;
-
-	iov_iter_advance(iter, sz - sizeof(*hdr));
-
-	return 0;
-}
-
-static int tun_vnet_hdr_to_skb(unsigned int flags, struct sk_buff *skb,
-			       const struct virtio_net_hdr *hdr)
-{
-	return virtio_net_hdr_to_skb(skb, hdr, tun_is_little_endian(flags));
-}
-
-static int tun_vnet_hdr_from_skb(unsigned int flags,
-				 const struct net_device *dev,
-				 const struct sk_buff *skb,
-				 struct virtio_net_hdr *hdr)
-{
-	int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
-
-	if (virtio_net_hdr_from_skb(skb, hdr,
-				    tun_is_little_endian(flags), true,
-				    vlan_hlen)) {
-		struct skb_shared_info *sinfo = skb_shinfo(skb);
-
-		if (net_ratelimit()) {
-			netdev_err(dev, "unexpected GSO type: 0x%x, gso_size %d, hdr_len %d\n",
-				   sinfo->gso_type, tun16_to_cpu(flags, hdr->gso_size),
-				   tun16_to_cpu(flags, hdr->hdr_len));
-			print_hex_dump(KERN_ERR, "tun: ",
-				       DUMP_PREFIX_NONE,
-				       16, 1, skb->head,
-				       min(tun16_to_cpu(flags, hdr->hdr_len), 64), true);
-		}
-		WARN_ON_ONCE(1);
-		return -EINVAL;
-	}
-
-	return 0;
-}
-
 static inline u32 tun_hashfn(u32 rxhash)
 {
 	return rxhash & TUN_MASK_FLOW_ENTRIES;
diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
new file mode 100644
index 000000000000..fd7411c4447f
--- /dev/null
+++ b/drivers/net/tun_vnet.h
@@ -0,0 +1,185 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef TUN_VNET_H
+#define TUN_VNET_H
+
+/* High bits in flags field are unused. */
+#define TUN_VNET_LE     0x80000000
+#define TUN_VNET_BE     0x40000000
+
+static inline bool tun_vnet_legacy_is_little_endian(unsigned int flags)
+{
+	bool be = IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) &&
+		  (flags & TUN_VNET_BE);
+
+	return !be && virtio_legacy_is_little_endian();
+}
+
+static inline long tun_get_vnet_be(unsigned int flags, int __user *argp)
+{
+	int be = !!(flags & TUN_VNET_BE);
+
+	if (!IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE))
+		return -EINVAL;
+
+	if (put_user(be, argp))
+		return -EFAULT;
+
+	return 0;
+}
+
+static inline long tun_set_vnet_be(unsigned int *flags, int __user *argp)
+{
+	int be;
+
+	if (!IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE))
+		return -EINVAL;
+
+	if (get_user(be, argp))
+		return -EFAULT;
+
+	if (be)
+		*flags |= TUN_VNET_BE;
+	else
+		*flags &= ~TUN_VNET_BE;
+
+	return 0;
+}
+
+static inline bool tun_vnet_is_little_endian(unsigned int flags)
+{
+	return flags & TUN_VNET_LE || tun_vnet_legacy_is_little_endian(flags);
+}
+
+static inline u16 tun_vnet16_to_cpu(unsigned int flags, __virtio16 val)
+{
+	return __virtio16_to_cpu(tun_vnet_is_little_endian(flags), val);
+}
+
+static inline __virtio16 cpu_to_tun_vnet16(unsigned int flags, u16 val)
+{
+	return __cpu_to_virtio16(tun_vnet_is_little_endian(flags), val);
+}
+
+static inline long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags,
+				  unsigned int cmd, int __user *sp)
+{
+	int s;
+
+	switch (cmd) {
+	case TUNGETVNETHDRSZ:
+		s = *vnet_hdr_sz;
+		if (put_user(s, sp))
+			return -EFAULT;
+		return 0;
+
+	case TUNSETVNETHDRSZ:
+		if (get_user(s, sp))
+			return -EFAULT;
+		if (s < (int)sizeof(struct virtio_net_hdr))
+			return -EINVAL;
+
+		*vnet_hdr_sz = s;
+		return 0;
+
+	case TUNGETVNETLE:
+		s = !!(*flags & TUN_VNET_LE);
+		if (put_user(s, sp))
+			return -EFAULT;
+		return 0;
+
+	case TUNSETVNETLE:
+		if (get_user(s, sp))
+			return -EFAULT;
+		if (s)
+			*flags |= TUN_VNET_LE;
+		else
+			*flags &= ~TUN_VNET_LE;
+		return 0;
+
+	case TUNGETVNETBE:
+		return tun_get_vnet_be(*flags, sp);
+
+	case TUNSETVNETBE:
+		return tun_set_vnet_be(flags, sp);
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
+				   struct iov_iter *from,
+				   struct virtio_net_hdr *hdr)
+{
+	u16 hdr_len;
+
+	if (iov_iter_count(from) < sz)
+		return -EINVAL;
+
+	if (!copy_from_iter_full(hdr, sizeof(*hdr), from))
+		return -EFAULT;
+
+	hdr_len = tun_vnet16_to_cpu(flags, hdr->hdr_len);
+
+	if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
+		hdr_len = max(tun_vnet16_to_cpu(flags, hdr->csum_start) + tun_vnet16_to_cpu(flags, hdr->csum_offset) + 2, hdr_len);
+		hdr->hdr_len = cpu_to_tun_vnet16(flags, hdr_len);
+	}
+
+	if (hdr_len > iov_iter_count(from))
+		return -EINVAL;
+
+	iov_iter_advance(from, sz - sizeof(*hdr));
+
+	return hdr_len;
+}
+
+static inline int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
+				   const struct virtio_net_hdr *hdr)
+{
+	if (unlikely(iov_iter_count(iter) < sz))
+		return -EINVAL;
+
+	if (unlikely(copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr)))
+		return -EFAULT;
+
+	iov_iter_advance(iter, sz - sizeof(*hdr));
+
+	return 0;
+}
+
+static inline int tun_vnet_hdr_to_skb(unsigned int flags, struct sk_buff *skb,
+				      const struct virtio_net_hdr *hdr)
+{
+	return virtio_net_hdr_to_skb(skb, hdr, tun_vnet_is_little_endian(flags));
+}
+
+static inline int tun_vnet_hdr_from_skb(unsigned int flags,
+					const struct net_device *dev,
+					const struct sk_buff *skb,
+					struct virtio_net_hdr *hdr)
+{
+	int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
+
+	if (virtio_net_hdr_from_skb(skb, hdr,
+				    tun_vnet_is_little_endian(flags), true,
+				    vlan_hlen)) {
+		struct skb_shared_info *sinfo = skb_shinfo(skb);
+
+		if (net_ratelimit()) {
+			netdev_err(dev, "unexpected GSO type: 0x%x, gso_size %d, hdr_len %d\n",
+				   sinfo->gso_type, tun_vnet16_to_cpu(flags, hdr->gso_size),
+				   tun_vnet16_to_cpu(flags, hdr->hdr_len));
+			print_hex_dump(KERN_ERR, "tun: ",
+				       DUMP_PREFIX_NONE,
+				       16, 1, skb->head,
+				       min(tun_vnet16_to_cpu(flags, hdr->hdr_len), 64), true);
+		}
+		WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+#endif /* TUN_VNET_H */