Re: [PATCH net] tcp: fix potential huge kmalloc() calls in TCP_REPAIR

[Pavel Emelyanov <xemul@parallels.com>]

On 11/19/2015 08:03 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> 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.

Doesn't the tcp_try_rmem_schedule() protect us from doing this "eventually"?
I mean first we would be allowed to do it, but then the sock will be charged
with the previous allocations and will not add more memory to socket.

Nonetheless,

Acked-by: Pavel Emelyanov <xemul@parallels.com>

> - 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@google.com>
> Cc: Pavel Emelyanov <xemul@parallels.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 fdd88c3803a6..a4a0b6b3bcf2 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -4481,19 +4481,34 @@ 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;
> @@ -4509,7 +4524,8 @@ 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)
> 
> 
> .
>