net: add skb_dst_force() in sock_queue_err_skb()

Commit 7fee226ad239 (add a noref bit on skb dst) forgot to use
skb_dst_force() on packets queued in sk_error_queue

This triggers following warning, for applications using IP_CMSG_PKTINFO
receiving one error status


------------[ cut here ]------------
WARNING: at include/linux/skbuff.h:457 ip_cmsg_recv_pktinfo+0xa6/0xb0()
Hardware name: 2669UYD
Modules linked in: isofs vboxnetadp vboxnetflt nfsd ebtable_nat ebtables
lib80211_crypt_ccmp uinput xcbc hdaps tp_smapi thinkpad_ec radeonfb fb_ddc
radeon ttm drm_kms_helper drm ipw2200 intel_agp intel_gtt libipw i2c_algo_bit
i2c_i801 agpgart rng_core cfbfillrect cfbcopyarea cfbimgblt video raid10 raid1
raid0 linear md_mod vboxdrv
Pid: 4697, comm: miredo Not tainted 2.6.39-rc6-00569-g5895198-dirty #22
Call Trace:
 [<c17746b6>] ? printk+0x1d/0x1f
 [<c1058302>] warn_slowpath_common+0x72/0xa0
 [<c15bbca6>] ? ip_cmsg_recv_pktinfo+0xa6/0xb0
 [<c15bbca6>] ? ip_cmsg_recv_pktinfo+0xa6/0xb0
 [<c1058350>] warn_slowpath_null+0x20/0x30
 [<c15bbca6>] ip_cmsg_recv_pktinfo+0xa6/0xb0
 [<c15bbdd7>] ip_cmsg_recv+0x127/0x260
 [<c154f82d>] ? skb_dequeue+0x4d/0x70
 [<c1555523>] ? skb_copy_datagram_iovec+0x53/0x300
 [<c178e834>] ? sub_preempt_count+0x24/0x50
 [<c15bdd2d>] ip_recv_error+0x23d/0x270
 [<c15de554>] udp_recvmsg+0x264/0x2b0
 [<c15ea659>] inet_recvmsg+0xd9/0x130
 [<c1547752>] sock_recvmsg+0xf2/0x120
 [<c11179cb>] ? might_fault+0x4b/0xa0
 [<c15546bc>] ? verify_iovec+0x4c/0xc0
 [<c1547660>] ? sock_recvmsg_nosec+0x100/0x100
 [<c1548294>] __sys_recvmsg+0x114/0x1e0
 [<c1093895>] ? __lock_acquire+0x365/0x780
 [<c1148b66>] ? fget_light+0xa6/0x3e0
 [<c1148b7f>] ? fget_light+0xbf/0x3e0
 [<c1148aee>] ? fget_light+0x2e/0x3e0
 [<c1549f29>] sys_recvmsg+0x39/0x60

Close bug https://bugzilla.kernel.org/show_bug.cgi?id=34622


Reported-by: Witold Baryluk <baryluk@smp.if.uj.edu.pl>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -2993,6 +2993,9 @@ int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
 	skb->destructor = sock_rmem_free;
 	atomic_add(skb->truesize, &sk->sk_rmem_alloc);
 
+	/* before exiting rcu section, make sure dst is refcounted */
+	skb_dst_force(skb);
+
 	skb_queue_tail(&sk->sk_error_queue, skb);
 	if (!sock_flag(sk, SOCK_DEAD))
 		sk->sk_data_ready(sk, skb->len);