On Thu, Sep 08, 2016 at 05:49:04PM +0800, Xin Long wrote:
> Now sctp uses the transport without holding it in sctp_hash_cmp,
> it can cause a use-after-free panic. As after it get transport from
> hashtable, another CPU may free it, then the members it accesses
> may be unavailable memory.
>
> This patch is to use sctp_transport_hold, in which it checks the
> refcnt first, holds it if it's not 0.
>
> Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
> ---
> net/sctp/input.c | 27 +++++++++++++++++----------
> 1 file changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index 69444d3..1555fb8 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -796,27 +796,34 @@ struct sctp_hash_cmp_arg {
> static inline int sctp_hash_cmp(struct rhashtable_compare_arg *arg,
> const void *ptr)
> {
> + struct sctp_transport *t = (struct sctp_transport *)ptr;
> const struct sctp_hash_cmp_arg *x = arg->key;
> - const struct sctp_transport *t = ptr;
> - struct sctp_association *asoc = t->asoc;
> - const struct net *net = x->net;
> + struct sctp_association *asoc;
> + int err = 1;
>
> if (!sctp_cmp_addr_exact(&t->ipaddr, x->paddr))
> - return 1;
> - if (!net_eq(sock_net(asoc->base.sk), net))
> - return 1;
> + return err;
> + if (!sctp_transport_hold(t))
> + return err;
> +
> + asoc = t->asoc;
> + if (!net_eq(sock_net(asoc->base.sk), x->net))
> + goto out;
> if (x->ep) {
> if (x->ep != asoc->ep)
> - return 1;
> + goto out;
> } else {
> if (x->laddr->v4.sin_port != htons(asoc->base.bind_addr.port))
> - return 1;
> + goto out;
> if (!sctp_bind_addr_match(&asoc->base.bind_addr,
> x->laddr, sctp_sk(asoc->base.sk)))
> - return 1;
> + goto out;
> }
>
> - return 0;
> + err = 0;
> +out:
> + sctp_transport_put(t);
> + return err;
> }
>
> static inline u32 sctp_hash_obj(const void *data, u32 len, u32 seed)
> --
> 2.1.0
>
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>
What path does this occur in? __sctp_lookup_association takes a hold on the
asoc, and that function is protected by the rcu_read_lock, so I'm not sure how
you get into a situation in which the asoc can be deleted while the lookup is
occuring.
Neil
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