netdev - [PATCH net 3/9] mptcp: sysctl: blackhole timeout: avoid using current->nsproxy

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Message-Id: <20250108-net-sysctl-current-nsproxy-v1-3-5df34b2083e8@kernel.org>
Date: Wed, 08 Jan 2025 16:34:31 +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 3/9] mptcp: sysctl: blackhole timeout: avoid using
 current->nsproxy

As mentioned in the previous commit, 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 'pernet' structure can be obtained from the table->data using
container_of().

Fixes: 27069e7cb3d1 ("mptcp: disable active MPTCP in case of blackhole")
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>
Reviewed-by: Mat Martineau <martineau@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/ctrl.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 81c30aa02196d69c55799e5963f6591e416c8831..b0dd008e2114bce65ee3906bbdc19a5a4316cefa 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -160,7 +160,9 @@ static int proc_blackhole_detect_timeout(const struct ctl_table *table,
 					 int write, void *buffer, size_t *lenp,
 					 loff_t *ppos)
 {
-	struct mptcp_pernet *pernet = mptcp_get_pernet(current->nsproxy->net_ns);
+	struct mptcp_pernet *pernet = container_of(table->data,
+						   struct mptcp_pernet,
+						   blackhole_timeout);
 	int ret;

 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

-- 
2.47.1