net: fix possible wrong checksum generation

Pravin Shelar mentioned that GSO could potentially generate
wrong TX checksum if skb has fragments that are overwritten
by the user between the checksum computation and transmit.

He suggested to linearize skbs but this extra copy can be
avoided for normal tcp skbs cooked by tcp_sendmsg().

This patch introduces a new SKB_GSO_SHARED_FRAG flag, set
in skb_shinfo(skb)->gso_type if at least one frag can be
modified by the user.

Typical sources of such possible overwrites are {vm}splice(),
sendfile(), and macvtap/tun/virtio_net drivers.

Tested:

$ netperf -H 7.7.8.84
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
7.7.8.84 () port 0 AF_INET
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.00    3959.52

$ netperf -H 7.7.8.84 -t TCP_SENDFILE
TCP SENDFILE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 7.7.8.84 ()
port 0 AF_INET
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.00    3216.80

Performance of the SENDFILE is impacted by the extra allocation and
copy, and because we use order-0 pages, while the TCP_STREAM uses
bigger pages.

Reported-by: Pravin Shelar <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 0f0f9ce3a7769ec552cc9f01f1915b44e44958fe..b181dfb3d6d600362235f7be38703a6827530f96 100644 (file)
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -543,6 +543,7 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                skb->data_len += len;
                skb->len += len;
                skb->truesize += truesize;
+               skb_shinfo(skb)->gso_type |= SKB_GSO_SHARED_FRAG;
                atomic_add(truesize, &skb->sk->sk_wmem_alloc);
                while (len) {
                        int off = base & ~PAGE_MASK;
@@ -598,7 +599,7 @@ static int macvtap_skb_from_vnet_hdr(struct sk_buff *skb,
 
        if (vnet_hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
                skb_shinfo(skb)->gso_size = vnet_hdr->gso_size;
-               skb_shinfo(skb)->gso_type = gso_type;
+               skb_shinfo(skb)->gso_type |= gso_type;
 
                /* Header must be checked, and gso_segs computed. */
                skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index c81680dc10eb7c43baaf61a0bfea1456dbe33c5c..293ce8dfc9e657206ebf2007800e3ffc397bb062 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1005,6 +1005,7 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                skb->data_len += len;
                skb->len += len;
                skb->truesize += truesize;
+               skb_shinfo(skb)->gso_type |= SKB_GSO_SHARED_FRAG;
                atomic_add(truesize, &skb->sk->sk_wmem_alloc);
                while (len) {
                        int off = base & ~PAGE_MASK;
@@ -1150,16 +1151,18 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
        }
 
        if (gso.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
+               unsigned short gso_type = 0;
+
                pr_debug("GSO!\n");
                switch (gso.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
                case VIRTIO_NET_HDR_GSO_TCPV4:
-                       skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
+                       gso_type = SKB_GSO_TCPV4;
                        break;
                case VIRTIO_NET_HDR_GSO_TCPV6:
-                       skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
+                       gso_type = SKB_GSO_TCPV6;
                        break;
                case VIRTIO_NET_HDR_GSO_UDP:
-                       skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
+                       gso_type = SKB_GSO_UDP;
                        break;
                default:
                        tun->dev->stats.rx_frame_errors++;
@@ -1168,9 +1171,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
                }
 
                if (gso.gso_type & VIRTIO_NET_HDR_GSO_ECN)
-                       skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
+                       gso_type |= SKB_GSO_TCP_ECN;
 
                skb_shinfo(skb)->gso_size = gso.gso_size;
+               skb_shinfo(skb)->gso_type |= gso_type;
                if (skb_shinfo(skb)->gso_size == 0) {
                        tun->dev->stats.rx_frame_errors++;
                        kfree_skb(skb);

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 701408a1ded6b50aae333b1cd709d9da7bfc35f8..58914c8ea68f8aec4a9ba0c98e33c4a50f1a3849 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -220,6 +220,7 @@ static void set_skb_frag(struct sk_buff *skb, struct page *page,
        skb->len += size;
        skb->truesize += PAGE_SIZE;
        skb_shinfo(skb)->nr_frags++;
+       skb_shinfo(skb)->gso_type |= SKB_GSO_SHARED_FRAG;
        *len -= size;
 }
 
@@ -379,16 +380,18 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
                 ntohs(skb->protocol), skb->len, skb->pkt_type);
 
        if (hdr->hdr.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
+               unsigned short gso_type = 0;
+
                pr_debug("GSO!\n");
                switch (hdr->hdr.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
                case VIRTIO_NET_HDR_GSO_TCPV4:
-                       skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
+                       gso_type = SKB_GSO_TCPV4;
                        break;
                case VIRTIO_NET_HDR_GSO_UDP:
-                       skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
+                       gso_type = SKB_GSO_UDP;
                        break;
                case VIRTIO_NET_HDR_GSO_TCPV6:
-                       skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
+                       gso_type = SKB_GSO_TCPV6;
                        break;
                default:
                        net_warn_ratelimited("%s: bad gso type %u.\n",
@@ -397,7 +400,7 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
                }
 
                if (hdr->hdr.gso_type & VIRTIO_NET_HDR_GSO_ECN)
-                       skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
+                       gso_type |= SKB_GSO_TCP_ECN;
 
                skb_shinfo(skb)->gso_size = hdr->hdr.gso_size;
                if (skb_shinfo(skb)->gso_size == 0) {
@@ -405,6 +408,7 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
                        goto frame_err;
                }
 
+               skb_shinfo(skb)->gso_type |= gso_type;
                /* Header must be checked, and gso_segs computed. */
                skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
                skb_shinfo(skb)->gso_segs = 0;

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8b2256e880e0ea135892b2deb5f5957dfc7568e9..0259b719bebf504d6ab7001a36a68cdebe41dacd 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -307,6 +307,13 @@ enum {
        SKB_GSO_TCPV6 = 1 << 4,
 
        SKB_GSO_FCOE = 1 << 5,
+
+       /* This indicates at least one fragment might be overwritten
+        * (as in vmsplice(), sendfile() ...)
+        * If we need to compute a TX checksum, we'll need to copy
+        * all frags to avoid possible bad checksum
+        */
+       SKB_GSO_SHARED_FRAG = 1 << 6,
 };
 
 #if BITS_PER_LONG > 32
@@ -2200,6 +2207,18 @@ static inline int skb_linearize(struct sk_buff *skb)
        return skb_is_nonlinear(skb) ? __skb_linearize(skb) : 0;
 }
 
+/**
+ * skb_has_shared_frag - can any frag be overwritten
+ * @skb: buffer to test
+ *
+ * Return true if the skb has at least one frag that might be modified
+ * by an external entity (as in vmsplice()/sendfile())
+ */
+static inline bool skb_has_shared_frag(const struct sk_buff *skb)
+{
+       return skb_shinfo(skb)->gso_type & SKB_GSO_SHARED_FRAG;
+}
+
 /**
  *     skb_linearize_cow - make sure skb is linear and writable
  *     @skb: buffer to process

diff --git a/net/core/dev.c b/net/core/dev.c
index c69cd8721b284051ee29febdb3f778ba1df2935a..a83375d3af72eb29e9939016666a0c6e745b8fdd 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2271,6 +2271,15 @@ int skb_checksum_help(struct sk_buff *skb)
                return -EINVAL;
        }
 
+       /* Before computing a checksum, we should make sure no frag could
+        * be modified by an external entity : checksum could be wrong.
+        */
+       if (skb_has_shared_frag(skb)) {
+               ret = __skb_linearize(skb);
+               if (ret)
+                       goto out;
+       }
+
        offset = skb_checksum_start_offset(skb);
        BUG_ON(offset >= skb_headlen(skb));
        csum = skb_checksum(skb, offset, skb->len - offset, 0);

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 2568c449fe36cb488269986402c31915d00ac647..bddc1dd2e7f221331136aec6e4b6efebdf4feb2c 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2340,6 +2340,8 @@ void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len)
 {
        int pos = skb_headlen(skb);
 
+       skb_shinfo(skb1)->gso_type = skb_shinfo(skb)->gso_type;
+
        if (len < pos)  /* Split line is inside header. */
                skb_split_inside_header(skb, skb1, len, pos);
        else            /* Second chunk has no header, nothing to copy. */
@@ -2845,6 +2847,8 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
                skb_copy_from_linear_data_offset(skb, offset,
                                                 skb_put(nskb, hsize), hsize);
 
+               skb_shinfo(nskb)->gso_type = skb_shinfo(skb)->gso_type;
+
                while (pos < offset + len && i < nfrags) {
                        *frag = skb_shinfo(skb)->frags[i];
                        __skb_frag_ref(frag);

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 4b70539199765de41e9356dfca738cb63ba7c16a..49ddca31c4daf4ac50923d540901b99f33a29f0e 100644 (file)
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1306,6 +1306,7 @@ static struct sk_buff *inet_gso_segment(struct sk_buff *skb,
                       SKB_GSO_UDP |
                       SKB_GSO_DODGY |
                       SKB_GSO_TCP_ECN |
+                      SKB_GSO_SHARED_FRAG |
                       0)))
                goto out;
 

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 303012adf9e6e0b442268b6f53b50ac8aea745fe..af6be70821c49557baf10a2d8e0ba8dc8916cdab 100644 (file)
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -738,7 +738,7 @@ drop:
 static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 {
        struct ip_tunnel *tunnel = netdev_priv(dev);
-       const struct iphdr  *old_iph = ip_hdr(skb);
+       const struct iphdr  *old_iph;
        const struct iphdr  *tiph;
        struct flowi4 fl4;
        u8     tos;
@@ -756,6 +756,8 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
            skb_checksum_help(skb))
                goto tx_error;
 
+       old_iph = ip_hdr(skb);
+
        if (dev->type == ARPHRD_ETHER)
                IPCB(skb)->flags = 0;
 

diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index 191fc24a745a9668332f74106fd39831d9f01c53..8f024d41eefa9d828af4969b84134e8c94087ffd 100644 (file)
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -472,7 +472,7 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
        __be16 df = tiph->frag_off;
        struct rtable *rt;                      /* Route to the other host */
        struct net_device *tdev;                /* Device to other host */
-       const struct iphdr  *old_iph = ip_hdr(skb);
+       const struct iphdr  *old_iph;
        struct iphdr  *iph;                     /* Our new IP header */
        unsigned int max_headroom;              /* The extra header space needed */
        __be32 dst = tiph->daddr;
@@ -486,6 +486,8 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
            skb_checksum_help(skb))
                goto tx_error;
 
+       old_iph = ip_hdr(skb);
+
        if (tos & 1)
                tos = old_iph->tos;
 

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 52271947a471355cad0688e061e731e7298121f6..3ec1f69c5ceb2ed0670c242c7eab2c0ac579c285 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -896,6 +896,8 @@ new_segment:
                        skb_fill_page_desc(skb, i, page, offset, copy);
                }
 
+               skb_shinfo(skb)->gso_type |= SKB_GSO_SHARED_FRAG;
+
                skb->len += copy;
                skb->data_len += copy;
                skb->truesize += copy;
@@ -3032,6 +3034,7 @@ struct sk_buff *tcp_tso_segment(struct sk_buff *skb,
                               SKB_GSO_DODGY |
                               SKB_GSO_TCP_ECN |
                               SKB_GSO_TCPV6 |
+                              SKB_GSO_SHARED_FRAG |
                               0) ||
                             !(type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))))
                        goto out;

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0905997e5873338d10f6a1d6bd22ece551cd5fb8..492c7cfe14532aed43a1df27c433c76b2ab4cf68 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1240,13 +1240,13 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
         */
        if (!skb_shinfo(prev)->gso_size) {
                skb_shinfo(prev)->gso_size = mss;
-               skb_shinfo(prev)->gso_type = sk->sk_gso_type;
+               skb_shinfo(prev)->gso_type |= sk->sk_gso_type;
        }
 
        /* CHECKME: To clear or not to clear? Mimics normal skb currently */
        if (skb_shinfo(skb)->gso_segs <= 1) {
                skb_shinfo(skb)->gso_size = 0;
-               skb_shinfo(skb)->gso_type = 0;
+               skb_shinfo(skb)->gso_type &= SKB_GSO_SHARED_FRAG;
        }
 
        /* Difference in this won't matter, both ACKed by the same cumul. ACK */

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 667a6adfccf89629360f824d814e66575c4994b1..367e2ec01da1f25afcf067351bf17ce673851af6 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1133,6 +1133,7 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
                                 unsigned int mss_now)
 {
+       skb_shinfo(skb)->gso_type &= SKB_GSO_SHARED_FRAG;
        if (skb->len <= mss_now || !sk_can_gso(sk) ||
            skb->ip_summed == CHECKSUM_NONE) {
                /* Avoid the costly divide in the normal
@@ -1140,11 +1141,10 @@ static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
                 */
                skb_shinfo(skb)->gso_segs = 1;
                skb_shinfo(skb)->gso_size = 0;
-               skb_shinfo(skb)->gso_type = 0;
        } else {
                skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
                skb_shinfo(skb)->gso_size = mss_now;
-               skb_shinfo(skb)->gso_type = sk->sk_gso_type;
+               skb_shinfo(skb)->gso_type |= sk->sk_gso_type;
        }
 }
 

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index f26f0da7f095763050d891e2543105c3f996320e..d141fc32a2eab7c41557488000e5811620ef799f 100644 (file)
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -100,6 +100,7 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
                       SKB_GSO_DODGY |
                       SKB_GSO_TCP_ECN |
                       SKB_GSO_TCPV6 |
+                      SKB_GSO_SHARED_FRAG |
                       0)))
                goto out;