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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        Xin Long <lucien.xin@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 199/240] sctp: fix a SCTP_MIB_CURRESTAB leak in sctp_sf_do_dupcook_b
Date:   Thu, 20 May 2021 11:23:11 +0200
Message-Id: <20210520092115.335834355@linuxfoundation.org>
In-Reply-To: <20210520092108.587553970@linuxfoundation.org>
References: <20210520092108.587553970@linuxfoundation.org>
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From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit f282df0391267fb2b263da1cc3233aa6fb81defc ]

Normally SCTP_MIB_CURRESTAB is always incremented once asoc enter into
ESTABLISHED from the state < ESTABLISHED and decremented when the asoc
is being deleted.

However, in sctp_sf_do_dupcook_b(), the asoc's state can be changed to
ESTABLISHED from the state >= ESTABLISHED where it shouldn't increment
SCTP_MIB_CURRESTAB. Otherwise, one asoc may increment MIB_CURRESTAB
multiple times but only decrement once at the end.

I was able to reproduce it by using scapy to do the 4-way shakehands,
after that I replayed the COOKIE-ECHO chunk with 'peer_vtag' field
changed to different values, and SCTP_MIB_CURRESTAB was incremented
multiple times and never went back to 0 even when the asoc was freed.

This patch is to fix it by only incrementing SCTP_MIB_CURRESTAB when
the state < ESTABLISHED in sctp_sf_do_dupcook_b().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sctp/sm_statefuns.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 146b568962e0..9045f6bcb34c 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -1851,7 +1851,8 @@ static sctp_disposition_t sctp_sf_do_dupcook_b(struct net *net,
 	sctp_add_cmd_sf(commands, SCTP_CMD_UPDATE_ASSOC, SCTP_ASOC(new_asoc));
 	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_STATE,
 			SCTP_STATE(SCTP_STATE_ESTABLISHED));
-	SCTP_INC_STATS(net, SCTP_MIB_CURRESTAB);
+	if (asoc->state < SCTP_STATE_ESTABLISHED)
+		SCTP_INC_STATS(net, SCTP_MIB_CURRESTAB);
 	sctp_add_cmd_sf(commands, SCTP_CMD_HB_TIMERS_START, SCTP_NULL());
 
 	repl = sctp_make_cookie_ack(new_asoc, chunk);
-- 
2.30.2