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From:   Kleber Sacilotto de Souza <kleber.souza@canonical.com>
To:     netdev@vger.kernel.org
Cc:     Gerrit Renker <gerrit@erg.abdn.ac.uk>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Thadeu Lima de Souza Cascardo <cascardo@canonical.com>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        "Alexander A. Klimov" <grandmaster@al2klimov.de>,
        Kees Cook <keescook@chromium.org>,
        Eric Dumazet <edumazet@google.com>,
        Alexey Kodanev <alexey.kodanev@oracle.com>,
        dccp@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] dccp: ccid: move timers to struct dccp_sock
Date:   Tue, 13 Oct 2020 19:18:48 +0200
Message-Id: <20201013171849.236025-2-kleber.souza@canonical.com>
In-Reply-To: <20201013171849.236025-1-kleber.souza@canonical.com>
References: <20201013171849.236025-1-kleber.souza@canonical.com>
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From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

When dccps_hc_tx_ccid is freed, ccid timers may still trigger. The reason
del_timer_sync can't be used is because this relies on keeping a reference
to struct sock. But as we keep a pointer to dccps_hc_tx_ccid and free that
during disconnect, the timer should really belong to struct dccp_sock.

This addresses CVE-2020-16119.

Fixes: 839a6094140a (net: dccp: Convert timers to use timer_setup())
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
---
 include/linux/dccp.h   |  2 ++
 net/dccp/ccids/ccid2.c | 32 +++++++++++++++++++-------------
 net/dccp/ccids/ccid3.c | 30 ++++++++++++++++++++----------
 3 files changed, 41 insertions(+), 23 deletions(-)

diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index 07e547c02fd8..504afa1a4be6 100644
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -259,6 +259,7 @@ struct dccp_ackvec;
  * @dccps_sync_scheduled - flag which signals "send out-of-band message soon"
  * @dccps_xmitlet - tasklet scheduled by the TX CCID to dequeue data packets
  * @dccps_xmit_timer - used by the TX CCID to delay sending (rate-based pacing)
+ * @dccps_ccid_timer - used by the CCIDs
  * @dccps_syn_rtt - RTT sample from Request/Response exchange (in usecs)
  */
 struct dccp_sock {
@@ -303,6 +304,7 @@ struct dccp_sock {
 	__u8				dccps_sync_scheduled:1;
 	struct tasklet_struct		dccps_xmitlet;
 	struct timer_list		dccps_xmit_timer;
+	struct timer_list		dccps_ccid_timer;
 };
 
 static inline struct dccp_sock *dccp_sk(const struct sock *sk)
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 3da1f77bd039..dbca1f1e2449 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -126,21 +126,26 @@ static void dccp_tasklet_schedule(struct sock *sk)
 
 static void ccid2_hc_tx_rto_expire(struct timer_list *t)
 {
-	struct ccid2_hc_tx_sock *hc = from_timer(hc, t, tx_rtotimer);
-	struct sock *sk = hc->sk;
-	const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
+	struct dccp_sock *dp = from_timer(dp, t, dccps_ccid_timer);
+	struct sock *sk = (struct sock *)dp;
+	struct ccid2_hc_tx_sock *hc;
+	bool sender_was_blocked;
 
 	bh_lock_sock(sk);
+
+	if (inet_sk_state_load(sk) == DCCP_CLOSED)
+		goto out;
+
+	hc = ccid_priv(dp->dccps_hc_tx_ccid);
+	sender_was_blocked = ccid2_cwnd_network_limited(hc);
+
 	if (sock_owned_by_user(sk)) {
-		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + HZ / 5);
+		sk_reset_timer(sk, &dp->dccps_ccid_timer, jiffies + HZ / 5);
 		goto out;
 	}
 
 	ccid2_pr_debug("RTO_EXPIRE\n");
 
-	if (sk->sk_state == DCCP_CLOSED)
-		goto out;
-
 	/* back-off timer */
 	hc->tx_rto <<= 1;
 	if (hc->tx_rto > DCCP_RTO_MAX)
@@ -166,7 +171,7 @@ static void ccid2_hc_tx_rto_expire(struct timer_list *t)
 	if (sender_was_blocked)
 		dccp_tasklet_schedule(sk);
 	/* restart backed-off timer */
-	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
+	sk_reset_timer(sk, &dp->dccps_ccid_timer, jiffies + hc->tx_rto);
 out:
 	bh_unlock_sock(sk);
 	sock_put(sk);
@@ -330,7 +335,7 @@ static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
 	}
 #endif
 
-	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
+	sk_reset_timer(sk, &dp->dccps_ccid_timer, jiffies + hc->tx_rto);
 
 #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
 	do {
@@ -700,9 +705,9 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 
 	/* restart RTO timer if not all outstanding data has been acked */
 	if (hc->tx_pipe == 0)
-		sk_stop_timer(sk, &hc->tx_rtotimer);
+		sk_stop_timer(sk, &dp->dccps_ccid_timer);
 	else
-		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
+		sk_reset_timer(sk, &dp->dccps_ccid_timer, jiffies + hc->tx_rto);
 done:
 	/* check if incoming Acks allow pending packets to be sent */
 	if (sender_was_blocked && !ccid2_cwnd_network_limited(hc))
@@ -737,17 +742,18 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
 	hc->tx_last_cong = hc->tx_lsndtime = hc->tx_cwnd_stamp = ccid2_jiffies32;
 	hc->tx_cwnd_used = 0;
 	hc->sk		 = sk;
-	timer_setup(&hc->tx_rtotimer, ccid2_hc_tx_rto_expire, 0);
+	timer_setup(&dp->dccps_ccid_timer, ccid2_hc_tx_rto_expire, 0);
 	INIT_LIST_HEAD(&hc->tx_av_chunks);
 	return 0;
 }
 
 static void ccid2_hc_tx_exit(struct sock *sk)
 {
+	struct dccp_sock *dp = dccp_sk(sk);
 	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
 	int i;
 
-	sk_stop_timer(sk, &hc->tx_rtotimer);
+	sk_stop_timer(sk, &dp->dccps_ccid_timer);
 
 	for (i = 0; i < hc->tx_seqbufc; i++)
 		kfree(hc->tx_seqbuf[i]);
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index b9ee1a4a8955..685f4d046c0d 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -184,17 +184,24 @@ static inline void ccid3_hc_tx_update_win_count(struct ccid3_hc_tx_sock *hc,
 
 static void ccid3_hc_tx_no_feedback_timer(struct timer_list *t)
 {
-	struct ccid3_hc_tx_sock *hc = from_timer(hc, t, tx_no_feedback_timer);
-	struct sock *sk = hc->sk;
+	struct dccp_sock *dp = from_timer(dp, t, dccps_ccid_timer);
+	struct ccid3_hc_tx_sock *hc;
+	struct sock *sk = (struct sock *)dp;
 	unsigned long t_nfb = USEC_PER_SEC / 5;
 
 	bh_lock_sock(sk);
+
+	if (inet_sk_state_load(sk) == DCCP_CLOSED)
+		goto out;
+
 	if (sock_owned_by_user(sk)) {
 		/* Try again later. */
 		/* XXX: set some sensible MIB */
 		goto restart_timer;
 	}
 
+	hc = ccid_priv(dp->dccps_hc_tx_ccid);
+
 	ccid3_pr_debug("%s(%p, state=%s) - entry\n", dccp_role(sk), sk,
 		       ccid3_tx_state_name(hc->tx_state));
 
@@ -250,8 +257,8 @@ static void ccid3_hc_tx_no_feedback_timer(struct timer_list *t)
 		t_nfb = max(hc->tx_t_rto, 2 * hc->tx_t_ipi);
 
 restart_timer:
-	sk_reset_timer(sk, &hc->tx_no_feedback_timer,
-			   jiffies + usecs_to_jiffies(t_nfb));
+	sk_reset_timer(sk, &dp->dccps_ccid_timer,
+		       jiffies + usecs_to_jiffies(t_nfb));
 out:
 	bh_unlock_sock(sk);
 	sock_put(sk);
@@ -280,7 +287,7 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 		return -EBADMSG;
 
 	if (hc->tx_state == TFRC_SSTATE_NO_SENT) {
-		sk_reset_timer(sk, &hc->tx_no_feedback_timer, (jiffies +
+		sk_reset_timer(sk, &dp->dccps_ccid_timer, (jiffies +
 			       usecs_to_jiffies(TFRC_INITIAL_TIMEOUT)));
 		hc->tx_last_win_count	= 0;
 		hc->tx_t_last_win_count = now;
@@ -354,6 +361,7 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, unsigned int len)
 static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 {
 	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	struct dccp_sock *dp = dccp_sk(sk);
 	struct tfrc_tx_hist_entry *acked;
 	ktime_t now;
 	unsigned long t_nfb;
@@ -420,7 +428,7 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 			       (unsigned int)(hc->tx_x >> 6));
 
 	/* unschedule no feedback timer */
-	sk_stop_timer(sk, &hc->tx_no_feedback_timer);
+	sk_stop_timer(sk, &dp->dccps_ccid_timer);
 
 	/*
 	 * As we have calculated new ipi, delta, t_nom it is possible
@@ -445,8 +453,8 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 		       "expire in %lu jiffies (%luus)\n",
 		       dccp_role(sk), sk, usecs_to_jiffies(t_nfb), t_nfb);
 
-	sk_reset_timer(sk, &hc->tx_no_feedback_timer,
-			   jiffies + usecs_to_jiffies(t_nfb));
+	sk_reset_timer(sk, &dp->dccps_ccid_timer,
+		       jiffies + usecs_to_jiffies(t_nfb));
 }
 
 static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
@@ -488,21 +496,23 @@ static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
 
 static int ccid3_hc_tx_init(struct ccid *ccid, struct sock *sk)
 {
+	struct dccp_sock *dp = dccp_sk(sk);
 	struct ccid3_hc_tx_sock *hc = ccid_priv(ccid);
 
 	hc->tx_state = TFRC_SSTATE_NO_SENT;
 	hc->tx_hist  = NULL;
 	hc->sk	     = sk;
-	timer_setup(&hc->tx_no_feedback_timer,
+	timer_setup(&dp->dccps_ccid_timer,
 		    ccid3_hc_tx_no_feedback_timer, 0);
 	return 0;
 }
 
 static void ccid3_hc_tx_exit(struct sock *sk)
 {
+	struct dccp_sock *dp = dccp_sk(sk);
 	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
 
-	sk_stop_timer(sk, &hc->tx_no_feedback_timer);
+	sk_stop_timer(sk, &dp->dccps_ccid_timer);
 	tfrc_tx_hist_purge(&hc->tx_hist);
 }
 
-- 
2.25.1