netdev - Re: [PATCH] ipv4: synchronize bind() with RTM

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Date:	Thu, 21 Oct 2010 12:25:53 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Timo Teräs <timo.teras@....fi>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: synchronize bind() with RTM_NEWADDR notifications

Le jeudi 21 octobre 2010 à 13:12 +0300, Timo Teräs a écrit :
> Otherwise we have race condition to user land:
>  1. process A changes IP address
>  2. kernel sends RTM_NEWADDR
>  3. process B gets notification
>  4. process B tries to bind() to new IP but that fails with
> EADDRNOTAVAIL because FIB is not yet updated and inet_addr_type() in
> inet_bind() does not recognize the IP as local
>  5. kernel calls inetaddr_chain notifiers which updates FIB
> 
> IPv6 side seems to handle the notifications properly: bind()
> immediately after RTM_NEWADDR succeeds as expected. This is because
> ipv6_chk_addr() uses inet6_addr_lst which is updated before address
> notification.
> 
> Signed-off-by: Timo Teräs <timo.teras@....fi>
> ---
>  net/ipv4/af_inet.c  |    9 +++++++++
>  net/ipv6/af_inet6.c |    4 +++-
>  2 files changed, 12 insertions(+), 1 deletions(-)
> 
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 6a1100c..21200e4 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -466,6 +466,15 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
>  	if (addr_len < sizeof(struct sockaddr_in))
>  		goto out;
>  
> +	/* Acquire rtnl_lock to synchronize with possible simultaneous
> +	 * IP-address changes. This is needed because when RTM_NEWADDR
> +	 * is sent the new IP is not yet in FIB, but alas inet_addr_type
> +	 * checks the address type using FIB. Acquiring rtnl lock once
> +	 * makse sure that any address for which RTM_NEWADDR was sent
> +	 * earlier exists also in FIB. */
> +	rtnl_lock();
> +	rtnl_unlock();

You must be kidding ?

Really, this is a hot path...



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