Re: [PATCHv2 net] sctp: hold the transport before using it in sctp_hash_cmp
flat view
From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: 2016-09-12 18:45:08
Also in:
linux-sctp
On Sat, Sep 10, 2016 at 11:11:23PM +0800, Xin Long wrote:
Since commit 4f0087812648 ("sctp: apply rhashtable api to send/recv
path"), sctp uses transport rhashtable with .obj_cmpfn sctp_hash_cmp,
in which it compares the members of the transport with the rhashtable
args to check if it's the right transport.
But sctp uses the transport without holding it in sctp_hash_cmp, it can
cause a use-after-free panic. As after it gets transport from hashtable,
another CPU may close the sk and free the asoc. In sctp_association_free,
it frees all the transports, meanwhile, the assoc's refcnt may be reduced
to 0, assoc can be destroyed by sctp_association_destroy.
So after that, transport->assoc is actually an unavailable memory address
in sctp_hash_cmp. Although sctp_hash_cmp is under rcu_read_lock, it still
can not avoid this, as assoc is not freed by RCU.
This patch is to hold the transport before checking it's members with
sctp_transport_hold, in which it checks the refcnt first, holds it if
it's not 0.
Fixes: 4f0087812648 ("sctp: apply rhashtable api to send/recv path")
Signed-off-by: Xin Long <lucien.xin@gmail.com>Note that we cannot defer the free of the asoc too because that cause issues with port re-use (issue already hit and fixed in the past), as the port would be still in use during the RCU grace period. Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
quoted hunk ↗ jump to hunk
--- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html