[Devel] [PATCH RHEL7 COMMIT] ms/tcp: fix potential huge kmalloc() calls in TCP_REPAIR

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.10.1.vz7.85.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.10.1.vz7.85.13
------>
commit a91048c4e6ed3ef7bf68a156a56cba87167815f6
Author: Eric Dumazet <edumazet at google.com>
Date:   Wed Nov 18 21:03:33 2015 -0800

    ms/tcp: fix potential huge kmalloc() calls in TCP_REPAIR
    
    tcp_send_rcvq() is used for re-injecting data into tcp receive queue.
    
    Problems :
    
    - No check against size is performed, allowed user to fool kernel in
      attempting very large memory allocations, eventually triggering
      OOM when memory is fragmented.
    
    - In case of fault during the copy we do not return correct errno.
    
    Lets use alloc_skb_with_frags() to cook optimal skbs.
    
    Fixes: 292e8d8c8538 ("tcp: Move rcvq sending to tcp_input.c")
    Fixes: c0e88ff0f256 ("tcp: Repair socket queues")
    Signed-off-by: Eric Dumazet <edumazet at google.com>
    Cc: Pavel Emelyanov <xemul at parallels.com>
    Acked-by: Pavel Emelyanov <xemul at parallels.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    CRIU often triggers 8 order page allocation while restoring TCP sockets
    without this patch.
    https://jira.sw.ru/browse/PSBM-93672
    
    (cherry picked from commit 5d4c9bfbabdb1d497f21afd81501e5c54b0c85d9)
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 net/ipv4/tcp_input.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 015c6fd7ec83..d0a6f767189d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4470,19 +4470,34 @@ static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int
 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
 {
 	struct sk_buff *skb;
+	int err = -ENOMEM;
+	int data_len = 0;
 	bool fragstolen;
 
 	if (size == 0)
 		return 0;
 
-	skb = alloc_skb(size, sk->sk_allocation);
+	if (size > PAGE_SIZE) {
+		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
+
+		data_len = npages << PAGE_SHIFT;
+		size = data_len + (size & ~PAGE_MASK);
+	}
+	skb = alloc_skb_with_frags(size - data_len, data_len,
+				   PAGE_ALLOC_COSTLY_ORDER,
+				   &err, sk->sk_allocation);
 	if (!skb)
 		goto err;
 
+	skb_put(skb, size - data_len);
+	skb->data_len = data_len;
+	skb->len = size;
+
 	if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
 		goto err_free;
 
-	if (memcpy_from_msg(skb_put(skb, size), msg, size))
+	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
+	if (err)
 		goto err_free;
 
 	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
@@ -4498,7 +4513,8 @@ int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
 err_free:
 	kfree_skb(skb);
 err:
-	return -ENOMEM;
+	return err;
+
 }
 
 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)