diff mbox series

[RFC,v5,04/10] tun: Unify vnet implementation

Message ID 20241008-rss-v5-4-f3cf68df005d@daynix.com
State New
Headers show
Series tun: Introduce virtio-net hashing feature | expand

Commit Message

Akihiko Odaki Oct. 8, 2024, 6:54 a.m. UTC 
Both tun and tap exposes the same set of virtio-net-related features.
Unify their implementations to ease future changes.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 MAINTAINERS            |   1 +
 drivers/net/tap.c      | 172 ++++++----------------------------------
 drivers/net/tun.c      | 208 ++++++++-----------------------------------------
 drivers/net/tun_vnet.h | 181 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 238 insertions(+), 324 deletions(-)

Comments

Akihiko Odaki Oct. 12, 2024, 10:57 a.m. UTC | #1 
On 2024/10/09 22:55, Willem de Bruijn wrote:
> Akihiko Odaki wrote:
>> Both tun and tap exposes the same set of virtio-net-related features.
>> Unify their implementations to ease future changes.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>> ---
>>   MAINTAINERS            |   1 +
>>   drivers/net/tap.c      | 172 ++++++----------------------------------
>>   drivers/net/tun.c      | 208 ++++++++-----------------------------------------
>>   drivers/net/tun_vnet.h | 181 ++++++++++++++++++++++++++++++++++++++++++
> 
> Same point: should not be in a header.
> 
> Also: I've looked into deduplicating code between the various tun, tap
> and packet socket code as well.
> 
> In general it's a good idea. The main counter arguments is that such a
> break in continuity also breaks backporting fixes to stable. So the
> benefit must outweight that cost.
> 
> In this case, the benefits in terms of LoC are rather modest. Not sure
> it's worth it.
> 
> Even more importantly: are the two code paths that you deduplicate
> exactly identical? Often in the past the two subtly diverged over
> time, e.g., due to new features added only to one of the two.

I find extracting the virtio_net-related code into functions is 
beneficial. For example, tun_get_user() is a big function and extracting 
the virtio_net-related code into tun_vnet_hdr_get() will ease 
understanding tun_get_user() when you are not interested in virtio_net. 
If virtio_net is your interest, you can look at this group of functions 
to figure out how they interact with each other.

Currently, the extracted code is almost identical for tun and tap so 
they can share it. We can copy the code back (but keep functions as 
semantic units) if they diverge in the future.

> 
> If so, call out any behavioral changes to either as a result of
> deduplicating explicitly.

This adds an error message for GSO failure, which was missing for tap. I 
will note that in the next version.
Willem de Bruijn Oct. 12, 2024, 5:43 p.m. UTC | #2 
Akihiko Odaki wrote:
> On 2024/10/09 22:55, Willem de Bruijn wrote:
> > Akihiko Odaki wrote:
> >> Both tun and tap exposes the same set of virtio-net-related features.
> >> Unify their implementations to ease future changes.
> >>
> >> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> >> ---
> >>   MAINTAINERS            |   1 +
> >>   drivers/net/tap.c      | 172 ++++++----------------------------------
> >>   drivers/net/tun.c      | 208 ++++++++-----------------------------------------
> >>   drivers/net/tun_vnet.h | 181 ++++++++++++++++++++++++++++++++++++++++++
> > 
> > Same point: should not be in a header.
> > 
> > Also: I've looked into deduplicating code between the various tun, tap
> > and packet socket code as well.
> > 
> > In general it's a good idea. The main counter arguments is that such a
> > break in continuity also breaks backporting fixes to stable. So the
> > benefit must outweight that cost.
> > 
> > In this case, the benefits in terms of LoC are rather modest. Not sure
> > it's worth it.
> > 
> > Even more importantly: are the two code paths that you deduplicate
> > exactly identical? Often in the past the two subtly diverged over
> > time, e.g., due to new features added only to one of the two.
> 
> I find extracting the virtio_net-related code into functions is 
> beneficial.

I understand the benefits. But as I pointed out, it is a trade-off,
not an unconditional good.

> For example, tun_get_user() is a big function and extracting 
> the virtio_net-related code into tun_vnet_hdr_get() will ease 
> understanding tun_get_user() when you are not interested in virtio_net. 
> If virtio_net is your interest, you can look at this group of functions 
> to figure out how they interact with each other.
> 
> Currently, the extracted code is almost identical for tun and tap so 

Almost here is the scary part. Any code that is not exactly identical
must be called out in the commit message.

What often happened is that one of the two got an improvement, whether
fix or feature extension. Then it is likely acceptable to extend this
to the other, too. But we have to review each case.

> they can share it. We can copy the code back (but keep functions as 
> semantic units) if they diverge in the future.

There hopefully is no need to diverge in the future. I suspect that
all previous divergences are accidental.

> > 
> > If so, call out any behavioral changes to either as a result of
> > deduplicating explicitly.
> 
> This adds an error message for GSO failure, which was missing for tap. I 
> will note that in the next version.
diff mbox series

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index cc40a9d9b8cd..209b4e1cccb1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -23338,6 +23338,7 @@  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_vnet.h
 
 TURBOCHANNEL SUBSYSTEM
 M:	"Maciej W. Rozycki" <macro@orcam.me.uk>
diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 77574f7a3bd4..9a34ceed0c2c 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -26,74 +26,9 @@ 
 #include <linux/virtio_net.h>
 #include <linux/skb_array.h>
 
-#define TAP_IFFEATURES (IFF_VNET_HDR | IFF_MULTI_QUEUE)
-
-#define TAP_VNET_LE 0x80000000
-#define TAP_VNET_BE 0x40000000
-
-#ifdef CONFIG_TUN_VNET_CROSS_LE
-static inline bool tap_legacy_is_little_endian(struct tap_queue *q)
-{
-	return q->flags & TAP_VNET_BE ? false :
-		virtio_legacy_is_little_endian();
-}
-
-static long tap_get_vnet_be(struct tap_queue *q, int __user *sp)
-{
-	int s = !!(q->flags & TAP_VNET_BE);
-
-	if (put_user(s, sp))
-		return -EFAULT;
-
-	return 0;
-}
-
-static long tap_set_vnet_be(struct tap_queue *q, int __user *sp)
-{
-	int s;
-
-	if (get_user(s, sp))
-		return -EFAULT;
-
-	if (s)
-		q->flags |= TAP_VNET_BE;
-	else
-		q->flags &= ~TAP_VNET_BE;
-
-	return 0;
-}
-#else
-static inline bool tap_legacy_is_little_endian(struct tap_queue *q)
-{
-	return virtio_legacy_is_little_endian();
-}
-
-static long tap_get_vnet_be(struct tap_queue *q, int __user *argp)
-{
-	return -EINVAL;
-}
+#include "tun_vnet.h"
 
-static long tap_set_vnet_be(struct tap_queue *q, int __user *argp)
-{
-	return -EINVAL;
-}
-#endif /* CONFIG_TUN_VNET_CROSS_LE */
-
-static inline bool tap_is_little_endian(struct tap_queue *q)
-{
-	return q->flags & TAP_VNET_LE ||
-		tap_legacy_is_little_endian(q);
-}
-
-static inline u16 tap16_to_cpu(struct tap_queue *q, __virtio16 val)
-{
-	return __virtio16_to_cpu(tap_is_little_endian(q), val);
-}
-
-static inline __virtio16 cpu_to_tap16(struct tap_queue *q, u16 val)
-{
-	return __cpu_to_virtio16(tap_is_little_endian(q), val);
-}
+#define TAP_IFFEATURES (IFF_VNET_HDR | IFF_MULTI_QUEUE)
 
 static struct proto tap_proto = {
 	.name = "tap",
@@ -641,10 +576,10 @@  static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 	struct sk_buff *skb;
 	struct tap_dev *tap;
 	unsigned long total_len = iov_iter_count(from);
-	unsigned long len = total_len;
+	unsigned long len;
 	int err;
 	struct virtio_net_hdr vnet_hdr = { 0 };
-	int vnet_hdr_len = 0;
+	int hdr_len;
 	int copylen = 0;
 	int depth;
 	bool zerocopy = false;
@@ -652,38 +587,20 @@  static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 	enum skb_drop_reason drop_reason;
 
 	if (q->flags & IFF_VNET_HDR) {
-		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
-
-		err = -EINVAL;
-		if (len < vnet_hdr_len)
-			goto err;
-		len -= vnet_hdr_len;
-
-		err = -EFAULT;
-		if (!copy_from_iter_full(&vnet_hdr, sizeof(vnet_hdr), from))
-			goto err;
-		iov_iter_advance(from, vnet_hdr_len - sizeof(vnet_hdr));
-		if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
-		     tap16_to_cpu(q, vnet_hdr.csum_start) +
-		     tap16_to_cpu(q, vnet_hdr.csum_offset) + 2 >
-			     tap16_to_cpu(q, vnet_hdr.hdr_len))
-			vnet_hdr.hdr_len = cpu_to_tap16(q,
-				 tap16_to_cpu(q, vnet_hdr.csum_start) +
-				 tap16_to_cpu(q, vnet_hdr.csum_offset) + 2);
-		err = -EINVAL;
-		if (tap16_to_cpu(q, vnet_hdr.hdr_len) > len)
+		hdr_len = tun_vnet_hdr_get(READ_ONCE(q->vnet_hdr_sz), q->flags, from, &vnet_hdr);
+		if (hdr_len < 0) {
+			err = hdr_len;
 			goto err;
+		}
+	} else {
+		hdr_len = 0;
 	}
 
-	err = -EINVAL;
-	if (unlikely(len < ETH_HLEN))
-		goto err;
-
+	len = iov_iter_count(from);
 	if (msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
 		struct iov_iter i;
 
-		copylen = vnet_hdr.hdr_len ?
-			tap16_to_cpu(q, vnet_hdr.hdr_len) : GOODCOPY_LEN;
+		copylen = hdr_len ? hdr_len : GOODCOPY_LEN;
 		if (copylen > good_linear)
 			copylen = good_linear;
 		else if (copylen < ETH_HLEN)
@@ -697,7 +614,7 @@  static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 
 	if (!zerocopy) {
 		copylen = len;
-		linear = tap16_to_cpu(q, vnet_hdr.hdr_len);
+		linear = hdr_len;
 		if (linear > good_linear)
 			linear = good_linear;
 		else if (linear < ETH_HLEN)
@@ -732,9 +649,8 @@  static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 	}
 	skb->dev = tap->dev;
 
-	if (vnet_hdr_len) {
-		err = virtio_net_hdr_to_skb(skb, &vnet_hdr,
-					    tap_is_little_endian(q));
+	if (q->flags & IFF_VNET_HDR) {
+		err = tun_vnet_hdr_to_skb(q->flags, skb, &vnet_hdr);
 		if (err) {
 			rcu_read_unlock();
 			drop_reason = SKB_DROP_REASON_DEV_HDR;
@@ -797,23 +713,17 @@  static ssize_t tap_put_user(struct tap_queue *q,
 	int total;
 
 	if (q->flags & IFF_VNET_HDR) {
-		int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
 		struct virtio_net_hdr vnet_hdr;
 
 		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
-		if (iov_iter_count(iter) < vnet_hdr_len)
-			return -EINVAL;
-
-		if (virtio_net_hdr_from_skb(skb, &vnet_hdr,
-					    tap_is_little_endian(q), true,
-					    vlan_hlen))
-			BUG();
 
-		if (copy_to_iter(&vnet_hdr, sizeof(vnet_hdr), iter) !=
-		    sizeof(vnet_hdr))
-			return -EFAULT;
+		ret = tun_vnet_hdr_from_skb(q->flags, NULL, skb, &vnet_hdr);
+		if (ret < 0)
+			goto done;
 
-		iov_iter_advance(iter, vnet_hdr_len - sizeof(vnet_hdr));
+		ret = tun_vnet_hdr_put(vnet_hdr_len, iter, &vnet_hdr);
+		if (ret < 0)
+			goto done;
 	}
 	total = vnet_hdr_len;
 	total += skb->len;
@@ -1072,42 +982,6 @@  static long tap_ioctl(struct file *file, unsigned int cmd,
 		q->sk.sk_sndbuf = s;
 		return 0;
 
-	case TUNGETVNETHDRSZ:
-		s = q->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;
-
-		q->vnet_hdr_sz = s;
-		return 0;
-
-	case TUNGETVNETLE:
-		s = !!(q->flags & TAP_VNET_LE);
-		if (put_user(s, sp))
-			return -EFAULT;
-		return 0;
-
-	case TUNSETVNETLE:
-		if (get_user(s, sp))
-			return -EFAULT;
-		if (s)
-			q->flags |= TAP_VNET_LE;
-		else
-			q->flags &= ~TAP_VNET_LE;
-		return 0;
-
-	case TUNGETVNETBE:
-		return tap_get_vnet_be(q, sp);
-
-	case TUNSETVNETBE:
-		return tap_set_vnet_be(q, sp);
-
 	case TUNSETOFFLOAD:
 		/* let the user check for future flags */
 		if (arg & ~(TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 |
@@ -1151,7 +1025,7 @@  static long tap_ioctl(struct file *file, unsigned int cmd,
 		return ret;
 
 	default:
-		return -EINVAL;
+		return tun_vnet_ioctl(&q->vnet_hdr_sz, &q->flags, cmd, sp);
 	}
 }
 
@@ -1199,7 +1073,7 @@  static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp)
 	skb->protocol = eth_hdr(skb)->h_proto;
 
 	if (vnet_hdr_len) {
-		err = virtio_net_hdr_to_skb(skb, gso, tap_is_little_endian(q));
+		err = tun_vnet_hdr_to_skb(q->flags, skb, gso);
 		if (err)
 			goto err_kfree;
 	}
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1d06c560c5e6..dd8799d19518 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)
@@ -298,70 +297,6 @@  static bool tun_napi_frags_enabled(const struct tun_file *tfile)
 	return tfile->napi_frags_enabled;
 }
 
-#ifdef CONFIG_TUN_VNET_CROSS_LE
-static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
-{
-	return tun->flags & TUN_VNET_BE ? false :
-		virtio_legacy_is_little_endian();
-}
-
-static long tun_get_vnet_be(struct tun_struct *tun, int __user *argp)
-{
-	int be = !!(tun->flags & TUN_VNET_BE);
-
-	if (put_user(be, argp))
-		return -EFAULT;
-
-	return 0;
-}
-
-static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
-{
-	int be;
-
-	if (get_user(be, argp))
-		return -EFAULT;
-
-	if (be)
-		tun->flags |= TUN_VNET_BE;
-	else
-		tun->flags &= ~TUN_VNET_BE;
-
-	return 0;
-}
-#else
-static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
-{
-	return virtio_legacy_is_little_endian();
-}
-
-static long tun_get_vnet_be(struct tun_struct *tun, int __user *argp)
-{
-	return -EINVAL;
-}
-
-static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
-{
-	return -EINVAL;
-}
-#endif /* CONFIG_TUN_VNET_CROSS_LE */
-
-static inline bool tun_is_little_endian(struct tun_struct *tun)
-{
-	return tun->flags & TUN_VNET_LE ||
-		tun_legacy_is_little_endian(tun);
-}
-
-static inline u16 tun16_to_cpu(struct tun_struct *tun, __virtio16 val)
-{
-	return __virtio16_to_cpu(tun_is_little_endian(tun), val);
-}
-
-static inline __virtio16 cpu_to_tun16(struct tun_struct *tun, u16 val)
-{
-	return __cpu_to_virtio16(tun_is_little_endian(tun), val);
-}
-
 static inline u32 tun_hashfn(u32 rxhash)
 {
 	return rxhash & TUN_MASK_FLOW_ENTRIES;
@@ -1751,8 +1686,9 @@  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
 	struct sk_buff *skb;
 	size_t total_len = iov_iter_count(from);
-	size_t len = total_len, align = tun->align, linear;
+	size_t len, align = tun->align, linear;
 	struct virtio_net_hdr gso = { 0 };
+	int hdr_len;
 	int good_linear;
 	int copylen;
 	bool zerocopy = false;
@@ -1763,37 +1699,25 @@  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	enum skb_drop_reason drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
 
 	if (!(tun->flags & IFF_NO_PI)) {
-		if (len < sizeof(pi))
+		if (iov_iter_count(from) < sizeof(pi))
 			return -EINVAL;
-		len -= sizeof(pi);
 
 		if (!copy_from_iter_full(&pi, sizeof(pi), from))
 			return -EFAULT;
 	}
 
 	if (tun->flags & IFF_VNET_HDR) {
-		int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
-
-		if (len < vnet_hdr_sz)
-			return -EINVAL;
-		len -= vnet_hdr_sz;
-
-		if (!copy_from_iter_full(&gso, sizeof(gso), from))
-			return -EFAULT;
-
-		if ((gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
-		    tun16_to_cpu(tun, gso.csum_start) + tun16_to_cpu(tun, gso.csum_offset) + 2 > tun16_to_cpu(tun, gso.hdr_len))
-			gso.hdr_len = cpu_to_tun16(tun, tun16_to_cpu(tun, gso.csum_start) + tun16_to_cpu(tun, gso.csum_offset) + 2);
-
-		if (tun16_to_cpu(tun, gso.hdr_len) > len)
-			return -EINVAL;
-		iov_iter_advance(from, vnet_hdr_sz - sizeof(gso));
+		hdr_len = tun_vnet_hdr_get(READ_ONCE(tun->vnet_hdr_sz), tun->flags, from, &gso);
+		if (hdr_len < 0)
+			return hdr_len;
+	} else {
+		hdr_len = 0;
 	}
 
+	len = iov_iter_count(from);
 	if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) {
 		align += NET_IP_ALIGN;
-		if (unlikely(len < ETH_HLEN ||
-			     (gso.hdr_len && tun16_to_cpu(tun, gso.hdr_len) < ETH_HLEN)))
+		if (unlikely(len < ETH_HLEN || (hdr_len && hdr_len < ETH_HLEN)))
 			return -EINVAL;
 	}
 
@@ -1806,7 +1730,7 @@  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 		 * enough room for skb expand head in case it is used.
 		 * The rest of the buffer is mapped from userspace.
 		 */
-		copylen = gso.hdr_len ? tun16_to_cpu(tun, gso.hdr_len) : GOODCOPY_LEN;
+		copylen = hdr_len ? hdr_len : GOODCOPY_LEN;
 		if (copylen > good_linear)
 			copylen = good_linear;
 		linear = copylen;
@@ -1829,10 +1753,10 @@  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	} else {
 		if (!zerocopy) {
 			copylen = len;
-			if (tun16_to_cpu(tun, gso.hdr_len) > good_linear)
+			if (hdr_len > good_linear)
 				linear = good_linear;
 			else
-				linear = tun16_to_cpu(tun, gso.hdr_len);
+				linear = hdr_len;
 		}
 
 		if (frags) {
@@ -1867,7 +1791,7 @@  static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 		}
 	}
 
-	if (virtio_net_hdr_to_skb(skb, &gso, tun_is_little_endian(tun))) {
+	if (tun_vnet_hdr_to_skb(tun->flags, skb, &gso)) {
 		atomic_long_inc(&tun->rx_frame_errors);
 		err = -EINVAL;
 		goto free_skb;
@@ -2060,29 +1984,27 @@  static ssize_t tun_put_user_xdp(struct tun_struct *tun,
 				struct xdp_frame *xdp_frame,
 				struct iov_iter *iter)
 {
+	int ret;
 	int vnet_hdr_sz = 0;
 	size_t size = xdp_frame->len;
-	size_t ret;
+	size_t total;
 
 	if (tun->flags & IFF_VNET_HDR) {
 		struct virtio_net_hdr gso = { 0 };
 
 		vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
-		if (unlikely(iov_iter_count(iter) < vnet_hdr_sz))
-			return -EINVAL;
-		if (unlikely(copy_to_iter(&gso, sizeof(gso), iter) !=
-			     sizeof(gso)))
-			return -EFAULT;
-		iov_iter_advance(iter, vnet_hdr_sz - sizeof(gso));
+		ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
+		if (ret < 0)
+			return ret;
 	}
 
-	ret = copy_to_iter(xdp_frame->data, size, iter) + vnet_hdr_sz;
+	total = copy_to_iter(xdp_frame->data, size, iter) + vnet_hdr_sz;
 
 	preempt_disable();
-	dev_sw_netstats_tx_add(tun->dev, 1, ret);
+	dev_sw_netstats_tx_add(tun->dev, 1, total);
 	preempt_enable();
 
-	return ret;
+	return total;
 }
 
 /* Put packet to the user space buffer */
@@ -2096,6 +2018,7 @@  static ssize_t tun_put_user(struct tun_struct *tun,
 	int vlan_offset = 0;
 	int vlan_hlen = 0;
 	int vnet_hdr_sz = 0;
+	int ret;
 
 	if (skb_vlan_tag_present(skb))
 		vlan_hlen = VLAN_HLEN;
@@ -2122,31 +2045,13 @@  static ssize_t tun_put_user(struct tun_struct *tun,
 	if (vnet_hdr_sz) {
 		struct virtio_net_hdr gso;
 
-		if (iov_iter_count(iter) < vnet_hdr_sz)
-			return -EINVAL;
-
-		if (virtio_net_hdr_from_skb(skb, &gso,
-					    tun_is_little_endian(tun), true,
-					    vlan_hlen)) {
-			struct skb_shared_info *sinfo = skb_shinfo(skb);
-
-			if (net_ratelimit()) {
-				netdev_err(tun->dev, "unexpected GSO type: 0x%x, gso_size %d, hdr_len %d\n",
-					   sinfo->gso_type, tun16_to_cpu(tun, gso.gso_size),
-					   tun16_to_cpu(tun, gso.hdr_len));
-				print_hex_dump(KERN_ERR, "tun: ",
-					       DUMP_PREFIX_NONE,
-					       16, 1, skb->head,
-					       min((int)tun16_to_cpu(tun, gso.hdr_len), 64), true);
-			}
-			WARN_ON_ONCE(1);
-			return -EINVAL;
-		}
-
-		if (copy_to_iter(&gso, sizeof(gso), iter) != sizeof(gso))
-			return -EFAULT;
+		ret = tun_vnet_hdr_from_skb(tun->flags, tun->dev, skb, &gso);
+		if (ret < 0)
+			goto done;
 
-		iov_iter_advance(iter, vnet_hdr_sz - sizeof(gso));
+		ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
+		if (ret < 0)
+			goto done;
 	}
 
 	if (vlan_hlen) {
@@ -2506,7 +2411,7 @@  static int tun_xdp_one(struct tun_struct *tun,
 	skb_reserve(skb, xdp->data - xdp->data_hard_start);
 	skb_put(skb, xdp->data_end - xdp->data);
 
-	if (virtio_net_hdr_to_skb(skb, gso, tun_is_little_endian(tun))) {
+	if (tun_vnet_hdr_to_skb(tun->flags, skb, gso)) {
 		atomic_long_inc(&tun->rx_frame_errors);
 		kfree_skb(skb);
 		ret = -EINVAL;
@@ -3090,8 +2995,6 @@  static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	kgid_t group;
 	int ifindex;
 	int sndbuf;
-	int vnet_hdr_sz;
-	int le;
 	int ret;
 	bool do_notify = false;
 
@@ -3298,50 +3201,6 @@  static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		tun_set_sndbuf(tun);
 		break;
 
-	case TUNGETVNETHDRSZ:
-		vnet_hdr_sz = tun->vnet_hdr_sz;
-		if (copy_to_user(argp, &vnet_hdr_sz, sizeof(vnet_hdr_sz)))
-			ret = -EFAULT;
-		break;
-
-	case TUNSETVNETHDRSZ:
-		if (copy_from_user(&vnet_hdr_sz, argp, sizeof(vnet_hdr_sz))) {
-			ret = -EFAULT;
-			break;
-		}
-		if (vnet_hdr_sz < (int)sizeof(struct virtio_net_hdr)) {
-			ret = -EINVAL;
-			break;
-		}
-
-		tun->vnet_hdr_sz = vnet_hdr_sz;
-		break;
-
-	case TUNGETVNETLE:
-		le = !!(tun->flags & TUN_VNET_LE);
-		if (put_user(le, (int __user *)argp))
-			ret = -EFAULT;
-		break;
-
-	case TUNSETVNETLE:
-		if (get_user(le, (int __user *)argp)) {
-			ret = -EFAULT;
-			break;
-		}
-		if (le)
-			tun->flags |= TUN_VNET_LE;
-		else
-			tun->flags &= ~TUN_VNET_LE;
-		break;
-
-	case TUNGETVNETBE:
-		ret = tun_get_vnet_be(tun, argp);
-		break;
-
-	case TUNSETVNETBE:
-		ret = tun_set_vnet_be(tun, argp);
-		break;
-
 	case TUNATTACHFILTER:
 		/* Can be set only for TAPs */
 		ret = -EINVAL;
@@ -3397,8 +3256,7 @@  static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		break;
 
 	default:
-		ret = -EINVAL;
-		break;
+		ret = tun_vnet_ioctl(&tun->vnet_hdr_sz, &tun->flags, cmd, argp);
 	}
 
 	if (do_notify)
diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
new file mode 100644
index 000000000000..7c7f3f6d85e9
--- /dev/null
+++ b/drivers/net/tun_vnet.h
@@ -0,0 +1,181 @@ 
+/* 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)
+{
+	return !(IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) && (flags & TUN_VNET_BE)) &&
+	       virtio_legacy_is_little_endian();
+}
+
+static inline long tun_vnet_get_be(int flags, int __user *sp)
+{
+	int s = !!(flags & TUN_VNET_BE);
+
+	if (!IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE))
+		return -EINVAL;
+
+	if (put_user(s, sp))
+		return -EFAULT;
+
+	return 0;
+}
+
+static inline long tun_vnet_set_be(int *flags, int __user *sp)
+{
+	int s;
+
+	if (!IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE))
+		return -EINVAL;
+
+	if (get_user(s, sp))
+		return -EFAULT;
+
+	if (s)
+		*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 *sz, unsigned int *flags,
+				  unsigned int cmd, int __user *sp)
+{
+	int s;
+
+	switch (cmd) {
+	case TUNGETVNETHDRSZ:
+		s = *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;
+
+		*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_vnet_get_be(*flags, sp);
+
+	case TUNSETVNETBE:
+		return tun_vnet_set_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)
+{
+	if (iov_iter_count(from) < sz)
+		return -EINVAL;
+
+	if (!copy_from_iter_full(hdr, sizeof(*hdr), from))
+		return -EFAULT;
+
+	iov_iter_advance(from, sz - sizeof(*hdr));
+	if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
+	    tun_vnet16_to_cpu(flags, hdr->csum_start) +
+	    tun_vnet16_to_cpu(flags, hdr->csum_offset) + 2 >
+		     tun_vnet16_to_cpu(flags, hdr->hdr_len))
+		hdr->hdr_len = cpu_to_tun_vnet16(flags,
+						 tun_vnet16_to_cpu(flags, hdr->csum_start) +
+						 tun_vnet16_to_cpu(flags, hdr->csum_offset) + 2);
+	if (tun_vnet16_to_cpu(flags, hdr->hdr_len) > iov_iter_count(from))
+		return -EINVAL;
+
+	return tun_vnet16_to_cpu(flags, hdr->hdr_len);
+}
+
+static inline int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
+				   const struct virtio_net_hdr *hdr)
+{
+	if (iov_iter_count(iter) < sz)
+		return -EINVAL;
+
+	if (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 */