netdev - Re: [PATCH net] net: Set sk_prot_creator when cloning sockets to the right proto

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Date:   Tue, 26 Sep 2017 23:14:57 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Christoph Paasch <cpaasch@...le.com>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: Set sk_prot_creator when cloning sockets to
 the right proto

On Tue, 2017-09-26 at 17:38 -0700, Christoph Paasch wrote:
> sk->sk_prot and sk->sk_prot_creator can differ when the app uses
> IPV6_ADDRFORM (transforming an IPv6-socket to an IPv4-one).
> Which is why sk_prot_creator is there to make sure that sk_prot_free()
> does the kmem_cache_free() on the right kmem_cache slab.
> 
> Now, if such a socket gets transformed back to a listening socket (using
> connect() with AF_UNSPEC) we will allocate an IPv4 tcp_sock through
> sk_clone_lock() when a new connection comes in. But sk_prot_creator will
> still point to the IPv6 kmem_cache (as everything got copied in
> sk_clone_lock()). When freeing, we will thus put this
> memory back into the IPv6 kmem_cache although it was allocated in the
> IPv4 cache. I have seen memory corruption happening because of this.
> 
> With slub-debugging and MEMCG_KMEM enabled this gives the warning
> 	"cache_from_obj: Wrong slab cache. TCPv6 but object is from TCP"

Nice catch, thanks !

Reviewed-by: Eric Dumazet <edumazet@...gle.com>