netdev - [PATCH net] sctp: fix a SCTP_MIB_CURRESTAB leak in sctp_sf_do_dupcook

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Message-Id: <98b2f435ec48fba6c9bbb63908c887f15f67a98d.1619988080.git.lucien.xin@gmail.com>
Date:   Mon,  3 May 2021 04:41:20 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: [PATCH net] sctp: fix a SCTP_MIB_CURRESTAB leak in sctp_sf_do_dupcook_b

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@...il.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 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 5fc3f3a..fd1e319 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -1953,7 +1953,8 @@ static enum sctp_disposition sctp_sf_do_dupcook_b(

 	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());

 	/* Update the content of current association.  */
-- 
2.1.0