Re: [PATCH net] sctp: add the missing sock_owned_by_user check in sctp_icmp_redirect

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Wed, Oct 18, 2017 at 09:37:49PM +0800, Xin Long wrote:
> Now sctp processes icmp redirect packet in sctp_icmp_redirect where
> it calls sctp_transport_dst_check in which tp->dst can be released.
> 
> The problem is before calling sctp_transport_dst_check, it doesn't
> check sock_owned_by_user, which means tp->dst could be freed while
> a process is accessing it with owning the socket.
> 
> An use-after-free issue could be triggered by this.
> 
> This patch is to fix it by checking sock_owned_by_user before calling
> sctp_transport_dst_check in sctp_icmp_redirect, so that it would not
> release tp->dst if users still hold sock lock.
> 
> Besides, the same issue fixed in commit 45caeaa5ac0b ("dccp/tcp: fix
> routing redirect race") on sctp also needs this check.
> 
> Fixes: 55be7a9c6074 ("ipv4: Add redirect support to all protocol icmp error handlers")
> Reported-by: Eric Dumazet <edumazet@google.com>

Nice catch, btw.

> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Thanks

> ---
>  net/sctp/input.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index 92a0714..34f10e7 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -421,7 +421,7 @@ void sctp_icmp_redirect(struct sock *sk, struct sctp_transport *t,
>  {
>  	struct dst_entry *dst;
>  
> -	if (!t)
> +	if (sock_owned_by_user(sk) || !t)
>  		return;
>  	dst = sctp_transport_dst_check(t);
>  	if (dst)
> -- 
> 2.1.0
> 
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