On Tue, Feb 28, 2017 at 12:41:29PM +0800, Xin Long wrote:
> Commit cd2b70875058 ("sctp: check duplicate node before inserting a
> new transport") called rhltable_lookup() to check for the duplicate
> transport node in transport rhashtable.
>
> But rhltable_lookup() doesn't call rcu_read_lock inside, it could cause
> a use-after-free issue if it tries to dereference the node that another
> cpu has freed it. Note that sock lock can not avoid this as it is per
> sock.
>
> This patch is to fix it by calling rcu_read_lock before checking for
> duplicate transport nodes.
>
> Fixes: cd2b70875058 ("sctp: check duplicate node before inserting a new transport")
> Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
> ---
> net/sctp/input.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index fc45896..2a28ab2 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -884,14 +884,17 @@ int sctp_hash_transport(struct sctp_transport *t)
> arg.paddr = &t->ipaddr;
> arg.lport = htons(t->asoc->base.bind_addr.port);
>
> + rcu_read_lock();
> list = rhltable_lookup(&sctp_transport_hashtable, &arg,
> sctp_hash_params);
>
> rhl_for_each_entry_rcu(transport, tmp, list, node)
> if (transport->asoc->ep == t->asoc->ep) {
> + rcu_read_unlock();
> err = -EEXIST;
> goto out;
> }
> + rcu_read_unlock();
>
> err = rhltable_insert_key(&sctp_transport_hashtable, &arg,
> &t->node, sctp_hash_params);
> --
> 2.1.0
>
>
Hmm, rhltable_insert_key I think returns a pointer to the existing object in the
hash table if there is a collision (according to the _rhashtable_insert_fast
description). Wouldn't it be better to eliminate the rhl_for_each_entry_rcu
entirely, and just check the returned pointer from rhltable_insert_key?
Neil
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