sctp: kfree_rcu asoc

[ Upstream commit fb6df5a6234c38a9c551559506a49a677ac6f07a ]

In sctp_hash_transport/sctp_epaddr_lookup_transport, it dereferences
a transport's asoc under rcu_read_lock while asoc is freed not after
a grace period, which leads to a use-after-free panic.

This patch fixes it by calling kfree_rcu to make asoc be freed after
a grace period.

Note that only the asoc's memory is delayed to free in the patch, it
won't cause sk to linger longer.

Thanks Neil and Marcelo to make this clear.

Fixes: 7fda702f ("sctp: use new rhlist interface on sctp transport rhashtable")
Fixes: cd2b7087 ("sctp: check duplicate node before inserting a new transport")
Reported-by: syzbot+0b05d8aa7cb185107483@syzkaller.appspotmail.com
Reported-by: syzbot+aad231d51b1923158444@syzkaller.appspotmail.com
Suggested-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Acked-by: NMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: NNeil Horman <nhorman@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

include/net/sctp/structs.h

@@ -2075,6 +2075,8 @@ struct sctp_association {
 
 	__u64 abandoned_unsent[SCTP_PR_INDEX(MAX) + 1];
 	__u64 abandoned_sent[SCTP_PR_INDEX(MAX) + 1];
+
+	struct rcu_head rcu;
 };
 
 

net/sctp/associola.c

@@ -434,7 +434,7 @@ static void sctp_association_destroy(struct sctp_association *asoc)
 
 	WARN_ON(atomic_read(&asoc->rmem_alloc));
 
-	kfree(asoc);
+	kfree_rcu(asoc, rcu);
 	SCTP_DBG_OBJCNT_DEC(assoc);
 }