l2tp: dont play with skb->truesize

Andrew Savchenko reported a DNS failure and we diagnosed that
some UDP sockets were unable to send more packets because their
sk_wmem_alloc was corrupted after a while (tx_queue column in
following trace)

$ cat /proc/net/udp
  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode ref pointer drops
...
  459: 00000000:0270 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 4507 2 ffff88003d612380 0
  466: 00000000:0277 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 4802 2 ffff88003d613180 0
  470: 076A070A:007B 00000000:0000 07 FFFF4600:00000000 00:00000000 00000000   123        0 5552 2 ffff880039974380 0
  470: 010213AC:007B 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 4986 2 ffff88003dbd3180 0
  470: 010013AC:007B 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 4985 2 ffff88003dbd2e00 0
  470: 00FCA8C0:007B 00000000:0000 07 FFFFFB00:00000000 00:00000000 00000000     0        0 4984 2 ffff88003dbd2a80 0
...

Playing with skb->truesize is tricky, especially when
skb is attached to a socket, as we can fool memory charging.

Just remove this code, its not worth trying to be ultra
precise in xmit path.

Reported-by: Andrew Savchenko <bircoph@gmail.com>
Tested-by: Andrew Savchenko <bircoph@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 06389d5ff120bdee9ab09fe33de86d9a2854c13c..2ac884d0e89bd06ff820073351004509b0838902 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1168,8 +1168,6 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
        struct udphdr *uh;
        struct inet_sock *inet;
        __wsum csum;
-       int old_headroom;
-       int new_headroom;
        int headroom;
        int uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
        int udp_len;
@@ -1181,16 +1179,12 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
         */
        headroom = NET_SKB_PAD + sizeof(struct iphdr) +
                uhlen + hdr_len;
-       old_headroom = skb_headroom(skb);
        if (skb_cow_head(skb, headroom)) {
                kfree_skb(skb);
                return NET_XMIT_DROP;
        }
 
-       new_headroom = skb_headroom(skb);
        skb_orphan(skb);
-       skb->truesize += new_headroom - old_headroom;
-
        /* Setup L2TP header */
        session->build_header(session, __skb_push(skb, hdr_len));
 

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 286366ef8930a08981f04952d4459f2b9a413071..716605c241f482e4793e86bdb1dc61d1c3596602 100644 (file)
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -388,8 +388,6 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
        struct l2tp_session *session;
        struct l2tp_tunnel *tunnel;
        struct pppol2tp_session *ps;
-       int old_headroom;
-       int new_headroom;
        int uhlen, headroom;
 
        if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
@@ -408,7 +406,6 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
        if (tunnel == NULL)
                goto abort_put_sess;
 
-       old_headroom = skb_headroom(skb);
        uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
        headroom = NET_SKB_PAD +
                   sizeof(struct iphdr) + /* IP header */
@@ -418,9 +415,6 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
        if (skb_cow_head(skb, headroom))
                goto abort_put_sess_tun;
 
-       new_headroom = skb_headroom(skb);
-       skb->truesize += new_headroom - old_headroom;
-
        /* Setup PPP header */
        __skb_push(skb, sizeof(ppph));
        skb->data[0] = ppph[0];