From: Xin Long <lucien.xin@gmail.com>
Date: Sat, 1 Dec 2018 01:36:59 +0800
Subject: sctp: kfree_rcu asoc
Git-commit: fb6df5a6234c38a9c551559506a49a677ac6f07a
Patch-mainline: v4.20-rc6
References: networking-stable-18_12_12

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: 7fda702f9315 ("sctp: use new rhlist interface on sctp transport rhashtable")
Fixes: cd2b70875058 ("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: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 include/net/sctp/structs.h | 2 ++
 net/sctp/associola.c       | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index a11f93790476..feada358d872 100644
--- a/include/net/sctp/structs.h
+++ b/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;
 };
 
 
diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index dd77ec3892b6..914750b819b2 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -435,7 +435,7 @@ 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);
 }
 
-- 
2.20.1