Subject: Re: [PATCH] net: clean the sk_frag.page of new cloned socket

From: Eric Dumazet <[email-masked]>
Date: Thu, 25 Jan 2018 04:44:05 -0800

On Thu, 2018-01-25 at 20:08 +0800, Li RongQing wrote:
> Clean the sk_frag.page of new cloned socket, otherwise it will release
> twice wrongly since the reference count of this sk_frag page is not
> increased.
> 
> sk_clone_lock() is used to clone a new socket from sock which is in
> listening state and has not sk_frag.page, but a socket has sent data
> and can gets transformed back to a listening socket, will allocate an
> tcp_sock through sk_clone_lock() when a new connection comes in.
> 
> Signed-off-by: Li RongQing <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> ---
>  net/core/sock.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/core/sock.c b/net/core/sock.c
> index c0b5b2f17412..c845856f26da 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1738,6 +1738,8 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
>  		sk_refcnt_debug_inc(newsk);
>  		sk_set_socket(newsk, NULL);
>  		newsk->sk_wq = NULL;
> +		newsk->sk_frag.page = NULL;
> +		newsk->sk_frag.offset = 0;
>  
>  		if (newsk->sk_prot->sockets_allocated)
>  			sk_sockets_allocated_inc(newsk);

Good catch.

I suspect this was discovered by some syzkaller/syzbot run ?

I would rather move that in tcp_disconnect() that only fuzzers use,
instead of doing this on every clone and slowing down normal users.