linux-kernel - [PATCH net 5/9] sctp: sysctl: rto_min/max: avoid using current->nsproxy

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Message-Id: <20250108-net-sysctl-current-nsproxy-v1-5-5df34b2083e8@kernel.org>
Date: Wed, 08 Jan 2025 16:34:33 +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 5/9] sctp: sysctl: rto_min/max: 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 'net' structure can be obtained from the table->data using
container_of().

Note that table->data could also be used directly, as this is the only
member needed from the 'net' structure, but that would increase the size
of this fix, to use '*data' everywhere 'net->sctp.rto_min/max' is used.

Fixes: 4f3fdf3bc59c ("sctp: add check rto_min and rto_max in sysctl")
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/sctp/sysctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
index 9848d19630a4f760238a3a2abd3ec823f012d34a..a5285815264dfa9d88d1d71244f309448e97a506 100644
--- a/net/sctp/sysctl.c
+++ b/net/sctp/sysctl.c
@@ -433,7 +433,7 @@ static int proc_sctp_do_hmac_alg(const struct ctl_table *ctl, int write,
 static int proc_sctp_do_rto_min(const struct ctl_table *ctl, int write,
 				void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct net *net = current->nsproxy->net_ns;
+	struct net *net = container_of(ctl->data, struct net, sctp.rto_min);
 	unsigned int min = *(unsigned int *) ctl->extra1;
 	unsigned int max = *(unsigned int *) ctl->extra2;
 	struct ctl_table tbl;
@@ -461,7 +461,7 @@ static int proc_sctp_do_rto_min(const struct ctl_table *ctl, int write,
 static int proc_sctp_do_rto_max(const struct ctl_table *ctl, int write,
 				void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct net *net = current->nsproxy->net_ns;
+	struct net *net = container_of(ctl->data, struct net, sctp.rto_max);
 	unsigned int min = *(unsigned int *) ctl->extra1;
 	unsigned int max = *(unsigned int *) ctl->extra2;
 	struct ctl_table tbl;

-- 
2.47.1