[PATCH 5.16 041/285] net: initialize init_net earlier

Greg Kroah-Hartman
2022-04-12T07:43:14Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 9c1be1935fb68b2413796cdc03d019b8cf35ab51 ]

While testing a patch that will follow later
("net: add netns refcount tracker to struct nsproxy")
I found that devtmpfs_init() was called before init_net
was initialized.

This is a bug, because devtmpfs_setup() calls
ksys_unshare(CLONE_NEWNS);

This has the effect of increasing init_net refcount,
which will be later overwritten to 1, as part of setup_net(&init_net)

We had too many prior patches [1] trying to work around the root cause.

Really, make sure init_net is in BSS section, and that net_ns_init()
is called earlier at boot time.

Note that another patch ("vfs: add netns refcount tracker
to struct fs_context") also will need net_ns_init() being called
before vfs_caches_init()

As a bonus, this patch saves around 4KB in .data section.

[1]

f8c46cb39079 ("netns: do not call pernet ops for not yet set up init_net namespace")
b5082df8019a ("net: Initialise init_net.count to 1")
734b65417b24 ("net: Statically initialize init_net.dev_base_head")

v2: fixed a build error reported by kernel build bots (CONFIG_NET=n)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/net_namespace.h | 6 ++++++
init/main.c | 2 ++
net/core/dev.c | 3 +--
net/core/net_namespace.c | 17 +++++------------
4 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index bb5fa5914032..2ba326f9e004 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -479,4 +479,10 @@ static inline void fnhe_genid_bump(struct net *net)
atomic_inc(&net->fnhe_genid);
}

+#ifdef CONFIG_NET
+void net_ns_init(void);
+#else
+static inline void net_ns_init(void) {}
+#endif
+
#endif /* __NET_NET_NAMESPACE_H */
diff --git a/init/main.c b/init/main.c
index bb984ed79de0..cb68bc48a682 100644
--- a/init/main.c
+++ b/init/main.c
@@ -99,6 +99,7 @@
#include <linux/kcsan.h>
#include <linux/init_syscalls.h>
#include <linux/stackdepot.h>
+#include <net/net_namespace.h>

#include <asm/io.h>
#include <asm/bugs.h>
@@ -1113,6 +1114,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
key_init();
security_init();
dbg_late_init();
+ net_ns_init();
vfs_caches_init();
pagecache_init();
signals_init();
diff --git a/net/core/dev.c b/net/core/dev.c
index 2078d04c6482..8c47e0f2075d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -11403,8 +11403,7 @@ static int __net_init netdev_init(struct net *net)
BUILD_BUG_ON(GRO_HASH_BUCKETS >
8 * sizeof_field(struct napi_struct, gro_bitmask));

- if (net != &init_net)
- INIT_LIST_HEAD(&net->dev_base_head);
+ INIT_LIST_HEAD(&net->dev_base_head);

net->dev_name_head = netdev_create_hash();
if (net->dev_name_head == NULL)
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 9702d2b0d920..9745cb6fdf51 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -44,13 +44,7 @@ EXPORT_SYMBOL_GPL(net_rwsem);
static struct key_tag init_net_key_domain = { .usage = REFCOUNT_INIT(1) };
#endif

-struct net init_net = {
- .ns.count = REFCOUNT_INIT(1),
- .dev_base_head = LIST_HEAD_INIT(init_net.dev_base_head),
-#ifdef CONFIG_KEYS
- .key_domain = &init_net_key_domain,
-#endif
-};
+struct net init_net;
EXPORT_SYMBOL(init_net);

static bool init_net_initialized;
@@ -1081,7 +1075,7 @@ static void rtnl_net_notifyid(struct net *net, int cmd, int id, u32 portid,
rtnl_set_sk_err(net, RTNLGRP_NSID, err);
}

-static int __init net_ns_init(void)
+void __init net_ns_init(void)
{
struct net_generic *ng;

@@ -1102,6 +1096,9 @@ static int __init net_ns_init(void)

rcu_assign_pointer(init_net.gen, ng);

+#ifdef CONFIG_KEYS
+ init_net.key_domain = &init_net_key_domain;
+#endif
down_write(&pernet_ops_rwsem);
if (setup_net(&init_net, &init_user_ns))
panic("Could not setup the initial network namespace");
@@ -1116,12 +1113,8 @@ static int __init net_ns_init(void)
RTNL_FLAG_DOIT_UNLOCKED);
rtnl_register(PF_UNSPEC, RTM_GETNSID, rtnl_net_getid, rtnl_net_dumpid,
RTNL_FLAG_DOIT_UNLOCKED);
-
- return 0;
}

-pure_initcall(net_ns_init);
-
static void free_exit_list(struct pernet_operations *ops, struct list_head *net_exit_list)
{
ops_pre_exit_list(ops, net_exit_list);
--
2.35.1