netdev - [PATCH net 9/9] rds: sysctl: rds_tcp_{rcv,snd}buf: avoid using current->nsproxy

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Message-Id: <20250108-net-sysctl-current-nsproxy-v1-9-5df34b2083e8@kernel.org>
Date: Wed, 08 Jan 2025 16:34:37 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>, 
 Geliang Tang <geliang@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Gregory Detal <gregory.detal@...il.com>, 
 Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, 
 Xin Long <lucien.xin@...il.com>, Vlad Yasevich <vyasevich@...il.com>, 
 Neil Horman <nhorman@...driver.com>, wangweidong <wangweidong1@...wei.com>, 
 Daniel Borkmann <daniel@...earbox.net>, Vlad Yasevich <vyasevic@...hat.com>, 
 Allison Henderson <allison.henderson@...cle.com>, 
 Sowmini Varadhan <sowmini.varadhan@...cle.com>, 
 Al Viro <viro@...iv.linux.org.uk>
Cc: Joel Granados <joel.granados@...nel.org>, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-sctp@...r.kernel.org, 
 linux-rdma@...r.kernel.org, rds-devel@....oracle.com, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, stable@...r.kernel.org
Subject: [PATCH net 9/9] rds: sysctl: rds_tcp_{rcv,snd}buf: avoid using
 current->nsproxy

As mentioned in a previous commit of this series, using the 'net'
structure via 'current' is not recommended for different reasons:

- Inconsistency: getting info from the reader's/writer's netns vs only
  from the opener's netns.

- current->nsproxy can be NULL in some cases, resulting in an 'Oops'
  (null-ptr-deref), e.g. when the current task is exiting, as spotted by
  syzbot [1] using acct(2).

The per-netns structure can be obtained from the table->data using
container_of(), then the 'net' one can be retrieved from the listen
socket (if available).

Fixes: c6a58ffed536 ("RDS: TCP: Add sysctl tunables for sndbuf/rcvbuf on rds-tcp socket")
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/67769ecb.050a0220.3a8527.003f.GAE@google.com [1]
Suggested-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/rds/tcp.c | 39 ++++++++++++++++++++++++++++++++-------
 1 file changed, 32 insertions(+), 7 deletions(-)

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 351ac1747224a3a1c8b0e297ba53cdbbcbc55401..0581c53e6517043ad6c2ad4207b26ab169989ed8 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -61,8 +61,10 @@ static atomic_t rds_tcp_unloading = ATOMIC_INIT(0);

 static struct kmem_cache *rds_tcp_conn_slab;

-static int rds_tcp_skbuf_handler(const struct ctl_table *ctl, int write,
-				 void *buffer, size_t *lenp, loff_t *fpos);
+static int rds_tcp_sndbuf_handler(const struct ctl_table *ctl, int write,
+				  void *buffer, size_t *lenp, loff_t *fpos);
+static int rds_tcp_rcvbuf_handler(const struct ctl_table *ctl, int write,
+				  void *buffer, size_t *lenp, loff_t *fpos);

 static int rds_tcp_min_sndbuf = SOCK_MIN_SNDBUF;
 static int rds_tcp_min_rcvbuf = SOCK_MIN_RCVBUF;
@@ -74,7 +76,7 @@ static struct ctl_table rds_tcp_sysctl_table[] = {
 		/* data is per-net pointer */
 		.maxlen         = sizeof(int),
 		.mode           = 0644,
-		.proc_handler   = rds_tcp_skbuf_handler,
+		.proc_handler   = rds_tcp_sndbuf_handler,
 		.extra1		= &rds_tcp_min_sndbuf,
 	},
 #define	RDS_TCP_RCVBUF	1
@@ -83,7 +85,7 @@ static struct ctl_table rds_tcp_sysctl_table[] = {
 		/* data is per-net pointer */
 		.maxlen         = sizeof(int),
 		.mode           = 0644,
-		.proc_handler   = rds_tcp_skbuf_handler,
+		.proc_handler   = rds_tcp_rcvbuf_handler,
 		.extra1		= &rds_tcp_min_rcvbuf,
 	},
 };
@@ -682,10 +684,10 @@ static void rds_tcp_sysctl_reset(struct net *net)
 	spin_unlock_irq(&rds_tcp_conn_lock);
 }

-static int rds_tcp_skbuf_handler(const struct ctl_table *ctl, int write,
+static int rds_tcp_skbuf_handler(struct rds_tcp_net *rtn,
+				 const struct ctl_table *ctl, int write,
 				 void *buffer, size_t *lenp, loff_t *fpos)
 {
-	struct net *net = current->nsproxy->net_ns;
 	int err;

 	err = proc_dointvec_minmax(ctl, write, buffer, lenp, fpos);
@@ -694,11 +696,34 @@ static int rds_tcp_skbuf_handler(const struct ctl_table *ctl, int write,
 			*(int *)(ctl->extra1));
 		return err;
 	}
-	if (write)
+
+	if (write && rtn->rds_tcp_listen_sock && rtn->rds_tcp_listen_sock->sk) {
+		struct net *net = sock_net(rtn->rds_tcp_listen_sock->sk);
+
 		rds_tcp_sysctl_reset(net);
+	}
+
 	return 0;
 }

+static int rds_tcp_sndbuf_handler(const struct ctl_table *ctl, int write,
+				  void *buffer, size_t *lenp, loff_t *fpos)
+{
+	struct rds_tcp_net *rtn = container_of(ctl->data, struct rds_tcp_net,
+					       sndbuf_size);
+
+	return rds_tcp_skbuf_handler(rtn, ctl, write, buffer, lenp, fpos);
+}
+
+static int rds_tcp_rcvbuf_handler(const struct ctl_table *ctl, int write,
+				  void *buffer, size_t *lenp, loff_t *fpos)
+{
+	struct rds_tcp_net *rtn = container_of(ctl->data, struct rds_tcp_net,
+					       rcvbuf_size);
+
+	return rds_tcp_skbuf_handler(rtn, ctl, write, buffer, lenp, fpos);
+}
+
 static void rds_tcp_exit(void)
 {
 	rds_tcp_set_unloading();

-- 
2.47.1