netdev - [PATCH v4 net 1/2] tcp: Fix use-after-free in inet_twsk

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Message-ID: <20240307232151.55963-2-kuniyu@amazon.com>
Date: Thu, 7 Mar 2024 15:21:50 -0800
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Allison Henderson <allison.henderson@...cle.com>
CC: Kuniyuki Iwashima <kuniyu@...zon.com>, Kuniyuki Iwashima
	<kuni1840@...il.com>, <netdev@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<rds-devel@....oracle.com>
Subject: [PATCH v4 net 1/2] tcp: Fix use-after-free in inet_twsk_purge().

Commit 740ea3c4a0b2 ("tcp: Clean up kernel listener's reqsk in
inet_twsk_purge()") added changes in inet_twsk_purge() to purge
reqsk in per-netns ehash during netns dismantle.

inet_csk_reqsk_queue_drop_and_put() will remove reqsk from per-netns
ehash, but the iteration uses sk_nulls_for_each_rcu(), which is not
safe.  After removing reqsk, we need to restart iteration.

Also, we need to use refcount_inc_not_zero() to check if reqsk is
freed by its timer.

Fixes: 740ea3c4a0b2 ("tcp: Clean up kernel listener's reqsk in inet_twsk_purge()")
Reported-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/ipv4/inet_timewait_sock.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 5befa4de5b24..c81f83893fc7 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -278,18 +278,32 @@ void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
 restart:
 		sk_nulls_for_each_rcu(sk, node, &head->chain) {
 			if (sk->sk_state != TCP_TIME_WAIT) {
+				struct request_sock *req;
+
+				if (likely(sk->sk_state != TCP_NEW_SYN_RECV))
+					continue;
+
 				/* A kernel listener socket might not hold refcnt for net,
 				 * so reqsk_timer_handler() could be fired after net is
 				 * freed.  Userspace listener and reqsk never exist here.
 				 */
-				if (unlikely(sk->sk_state == TCP_NEW_SYN_RECV &&
-					     hashinfo->pernet)) {
-					struct request_sock *req = inet_reqsk(sk);
 
-					inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
+				if (sk->sk_family != family ||
+				    refcount_read(&sock_net(sk)->ns.count))
+					continue;
+
+				req = inet_reqsk(sk);
+				if (unlikely(!refcount_inc_not_zero(&req->rsk_refcnt)))
+					continue;
+
+				if (unlikely(sk->sk_family != family ||
+					     refcount_read(&sock_net(sk)->ns.count))) {
+					reqsk_put(req);
+					continue;
 				}
 
-				continue;
+				inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
+				goto restart;
 			}
 
 			tw = inet_twsk(sk);
-- 
2.30.2