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From:   Chengfeng Ye <dg573847474@gmail.com>
To:     marcelo.leitner@gmail.com, lucien.xin@gmail.com,
        davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com
Cc:     linux-sctp@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Chengfeng Ye <dg573847474@gmail.com>
Subject: [PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq_lock
Date:   Tue, 27 Jun 2023 12:03:40 +0000
Message-Id: <20230627120340.19432-1-dg573847474@gmail.com>
Precedence: bulk

As &net->sctp.addr_wq_lock is also acquired by the timer
sctp_addr_wq_timeout_handler() in protocal.c, the same lock acquisition
at sctp_auto_asconf_init() seems should disable irq since it is called
from sctp_accept() under process context.

Possible deadlock scenario:
sctp_accept()
    -> sctp_sock_migrate()
    -> sctp_auto_asconf_init()
    -> spin_lock(&net->sctp.addr_wq_lock)
        <timer interrupt>
        -> sctp_addr_wq_timeout_handler()
        -> spin_lock_bh(&net->sctp.addr_wq_lock); (deadlock here)

This flaw was found using an experimental static analysis tool we are
developing for irq-related deadlock.

The tentative patch fix the potential deadlock by spin_lock_bh().

Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
 net/sctp/socket.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index cda8c2874691..b2c7d17ff848 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -364,9 +364,9 @@ static void sctp_auto_asconf_init(struct sctp_sock *sp)
 	struct net *net = sock_net(&sp->inet.sk);
 
 	if (net->sctp.default_auto_asconf) {
-		spin_lock(&net->sctp.addr_wq_lock);
+		spin_lock_bh(&net->sctp.addr_wq_lock);
 		list_add_tail(&sp->auto_asconf_list, &net->sctp.auto_asconf_splist);
-		spin_unlock(&net->sctp.addr_wq_lock);
+		spin_unlock_bh(&net->sctp.addr_wq_lock);
 		sp->do_auto_asconf = 1;
 	}
 }
-- 
2.17.1