From: Petar Penkov <peterpenkov96@gmail.com>
Date: Fri, 22 Sep 2017 13:49:15 -0700
Subject: tun: enable napi_gro_frags() for TUN/TAP driver
Patch-mainline: v4.15-rc1
Git-commit: 90e33d45940793def6f773b2d528e9f3c84ffdc7
References: bsc#1109837

Add a TUN/TAP receive mode that exercises the napi_gro_frags()
interface. This mode is available only in TAP mode, as the interface
expects packets with Ethernet headers.

Furthermore, packets follow the layout of the iovec_iter that was
received. The first iovec is the linear data, and every one after the
first is a fragment. If there are more fragments than the max number,
drop the packet. Additionally, invoke eth_get_headlen() to exercise flow
dissector code and to verify that the header resides in the linear data.

The napi_gro_frags() mode requires setting the IFF_NAPI_FRAGS option.
This is imposed because this mode is intended for testing via tools like
syzkaller and packetdrill, and the increased flexibility it provides can
introduce security vulnerabilities. This flag is accepted only if the
device is in TAP mode and has the IFF_NAPI flag set as well. This is
done because both of these are explicit requirements for correct
operation in this mode.

Signed-off-by: Petar Penkov <peterpenkov96@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: davem@davemloft.net
Cc: ppenkov@stanford.edu
Acked-by: Mahesh Bandewar <maheshb@google,com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/tun.c           |  134 ++++++++++++++++++++++++++++++++++++++++++--
 include/uapi/linux/if_tun.h |    1 
 2 files changed, 129 insertions(+), 6 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -75,6 +75,7 @@
 #include <linux/skb_array.h>
 #include <linux/bpf.h>
 #include <linux/bpf_trace.h>
+#include <linux/mutex.h>
 
 #include <linux/uaccess.h>
 
@@ -121,7 +122,8 @@ do {								\
 #define TUN_VNET_BE     0x40000000
 
 #define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
-		      IFF_MULTI_QUEUE | IFF_NAPI)
+		      IFF_MULTI_QUEUE | IFF_NAPI | IFF_NAPI_FRAGS)
+
 #define GOODCOPY_LEN 128
 
 #define FLT_EXACT_COUNT 8
@@ -173,6 +175,7 @@ struct tun_file {
 		unsigned int ifindex;
 	};
 	struct napi_struct napi;
+	struct mutex napi_mutex;	/* Protects access to the above napi */
 	struct list_head next;
 	struct tun_struct *detached;
 	struct skb_array tx_array;
@@ -277,6 +280,7 @@ static void tun_napi_init(struct tun_str
 		netif_napi_add(tun->dev, &tfile->napi, tun_napi_poll,
 			       NAPI_POLL_WEIGHT);
 		napi_enable(&tfile->napi);
+		mutex_init(&tfile->napi_mutex);
 	}
 }
 
@@ -292,6 +296,11 @@ static void tun_napi_del(struct tun_stru
 		netif_napi_del(&tfile->napi);
 }
 
+static bool tun_napi_frags_enabled(const struct tun_struct *tun)
+{
+	return READ_ONCE(tun->flags) & IFF_NAPI_FRAGS;
+}
+
 #ifdef CONFIG_TUN_VNET_CROSS_LE
 static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
 {
@@ -1036,7 +1045,8 @@ static void tun_poll_controller(struct n
 	 * supports polling, which enables bridge devices in virt setups to
 	 * still use netconsole
 	 * If NAPI is enabled, however, we need to schedule polling for all
-	 * queues.
+	 * queues unless we are using napi_gro_frags(), which we call in
+	 * process context and not in NAPI context.
 	 */
 	struct tun_struct *tun = netdev_priv(dev);
 
@@ -1044,6 +1054,9 @@ static void tun_poll_controller(struct n
 		struct tun_file *tfile;
 		int i;
 
+		if (tun_napi_frags_enabled(tun))
+			return;
+
 		rcu_read_lock();
 		for (i = 0; i < tun->numqueues; i++) {
 			tfile = rcu_dereference(tun->tfiles[i]);
@@ -1266,6 +1279,64 @@ static unsigned int tun_chr_poll(struct
 	return mask;
 }
 
+static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile,
+					    size_t len,
+					    const struct iov_iter *it)
+{
+	struct sk_buff *skb;
+	size_t linear;
+	int err;
+	int i;
+
+	if (it->nr_segs > MAX_SKB_FRAGS + 1)
+		return ERR_PTR(-ENOMEM);
+
+	local_bh_disable();
+	skb = napi_get_frags(&tfile->napi);
+	local_bh_enable();
+	if (!skb)
+		return ERR_PTR(-ENOMEM);
+
+	linear = iov_iter_single_seg_count(it);
+	err = __skb_grow(skb, linear);
+	if (err)
+		goto free;
+
+	skb->len = len;
+	skb->data_len = len - linear;
+	skb->truesize += skb->data_len;
+
+	for (i = 1; i < it->nr_segs; i++) {
+		size_t fragsz = it->iov[i].iov_len;
+		unsigned long offset;
+		struct page *page;
+		void *data;
+
+		if (fragsz == 0 || fragsz > PAGE_SIZE) {
+			err = -EINVAL;
+			goto free;
+		}
+
+		local_bh_disable();
+		data = napi_alloc_frag(fragsz);
+		local_bh_enable();
+		if (!data) {
+			err = -ENOMEM;
+			goto free;
+		}
+
+		page = virt_to_head_page(data);
+		offset = data - page_address(page);
+		skb_fill_page_desc(skb, i - 1, page, offset, fragsz);
+	}
+
+	return skb;
+free:
+	/* frees skb and all frags allocated with napi_alloc_frag() */
+	napi_free_frags(&tfile->napi);
+	return ERR_PTR(err);
+}
+
 /* prepad is the amount to reserve at front.  len is length after that.
  * linear is a hint as to how much to copy (usually headers). */
 static struct sk_buff *tun_alloc_skb(struct tun_file *tfile,
@@ -1478,6 +1549,7 @@ static ssize_t tun_get_user(struct tun_s
 	int err;
 	u32 rxhash;
 	int skb_xdp = 1;
+	bool frags = tun_napi_frags_enabled(tun);
 
 	if (!(tun->dev->flags & IFF_UP))
 		return -EIO;
@@ -1535,7 +1607,7 @@ static ssize_t tun_get_user(struct tun_s
 			zerocopy = true;
 	}
 
-	if (tun_can_build_skb(tun, tfile, len, noblock, zerocopy)) {
+	if (!frags && tun_can_build_skb(tun, tfile, len, noblock, zerocopy)) {
 		/* For the packet that is not easy to be processed
 		 * (e.g gso or jumbo packet), we will do it at after
 		 * skb was created with generic XDP routine.
@@ -1556,10 +1628,24 @@ static ssize_t tun_get_user(struct tun_s
 				linear = tun16_to_cpu(tun, gso.hdr_len);
 		}
 
-		skb = tun_alloc_skb(tfile, align, copylen, linear, noblock);
+		if (frags) {
+			mutex_lock(&tfile->napi_mutex);
+			skb = tun_napi_alloc_frags(tfile, copylen, from);
+			/* tun_napi_alloc_frags() enforces a layout for the skb.
+			 * If zerocopy is enabled, then this layout will be
+			 * overwritten by zerocopy_sg_from_iter().
+			 */
+			zerocopy = false;
+		} else {
+			skb = tun_alloc_skb(tfile, align, copylen, linear,
+					    noblock);
+		}
+
 		if (IS_ERR(skb)) {
 			if (PTR_ERR(skb) != -EAGAIN)
 				this_cpu_inc(tun->pcpu_stats->rx_dropped);
+			if (frags)
+				mutex_unlock(&tfile->napi_mutex);
 			return PTR_ERR(skb);
 		}
 
@@ -1571,6 +1657,11 @@ static ssize_t tun_get_user(struct tun_s
 		if (err) {
 			this_cpu_inc(tun->pcpu_stats->rx_dropped);
 			kfree_skb(skb);
+			if (frags) {
+				tfile->napi.skb = NULL;
+				mutex_unlock(&tfile->napi_mutex);
+			}
+
 			return -EFAULT;
 		}
 	}
@@ -1578,6 +1669,11 @@ static ssize_t tun_get_user(struct tun_s
 	if (virtio_net_hdr_to_skb(skb, &gso, tun_is_little_endian(tun))) {
 		this_cpu_inc(tun->pcpu_stats->rx_frame_errors);
 		kfree_skb(skb);
+		if (frags) {
+			tfile->napi.skb = NULL;
+			mutex_unlock(&tfile->napi_mutex);
+		}
+
 		return -EINVAL;
 	}
 
@@ -1605,7 +1701,8 @@ static ssize_t tun_get_user(struct tun_s
 		skb->dev = tun->dev;
 		break;
 	case IFF_TAP:
-		skb->protocol = eth_type_trans(skb, tun->dev);
+		if (!frags)
+			skb->protocol = eth_type_trans(skb, tun->dev);
 		break;
 	}
 
@@ -1640,7 +1737,23 @@ static ssize_t tun_get_user(struct tun_s
 
 	rxhash = __skb_get_hash_symmetric(skb);
 
-	if (tun->flags & IFF_NAPI) {
+	if (frags) {
+		/* Exercise flow dissector code path. */
+		u32 headlen = eth_get_headlen(skb->data, skb_headlen(skb));
+
+		if (headlen > skb_headlen(skb) || headlen < ETH_HLEN) {
+			this_cpu_inc(tun->pcpu_stats->rx_dropped);
+			napi_free_frags(&tfile->napi);
+			mutex_unlock(&tfile->napi_mutex);
+			WARN_ON(1);
+			return -ENOMEM;
+		}
+
+		local_bh_disable();
+		napi_gro_frags(&tfile->napi);
+		local_bh_enable();
+		mutex_unlock(&tfile->napi_mutex);
+	} else if (tun->flags & IFF_NAPI) {
 		struct sk_buff_head *queue = &tfile->sk.sk_write_queue;
 		int queue_len;
 
@@ -2063,6 +2176,15 @@ static int tun_set_iff(struct net *net,
 	if (tfile->detached)
 		return -EINVAL;
 
+	if ((ifr->ifr_flags & IFF_NAPI_FRAGS)) {
+		if (!capable(CAP_NET_ADMIN))
+			return -EPERM;
+
+		if (!(ifr->ifr_flags & IFF_NAPI) ||
+		    (ifr->ifr_flags & TUN_TYPE_MASK) != IFF_TAP)
+			return -EINVAL;
+	}
+
 	dev = __dev_get_by_name(net, ifr->ifr_name);
 	if (dev) {
 		if (ifr->ifr_flags & IFF_TUN_EXCL)
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -61,6 +61,7 @@
 #define IFF_TUN		0x0001
 #define IFF_TAP		0x0002
 #define IFF_NAPI	0x0010
+#define IFF_NAPI_FRAGS	0x0020
 #define IFF_NO_PI	0x1000
 /* This flag has no real effect */
 #define IFF_ONE_QUEUE	0x2000