Forwarded: [PATCH] nsfs: skip active reference management on initial namespaces

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Subject: [PATCH] nsfs: skip active reference management on initial namespaces
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master

Initial namespaces (init_net, init_uts_ns, init_pid_ns, etc.) are
statically allocated and exist for the entire lifetime of the system.
They should not participate in active reference counting.

When operations involve initial namespaces, both ns_ref_active_get()
and ns_ref_active_put() were managing active references on them.
This caused the active reference count to become imbalanced, leading
to warnings in __ns_ref_active_get() and __ns_ref_active_put().

Fix by adding is_initial_namespace() checks in both the
ns_ref_active_get and ns_ref_active_put macros. Initial namespaces
are now completely excluded from active reference management,
treating them as permanent kernel resources.

Reported-by: syzbot+0b2e79f91ff6579bfa5b@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 include/linux/ns_common.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index bd4492ef6ffc..b22c692b5f38 100644
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h
@@ -289,7 +289,10 @@ static __always_inline void __ns_ref_active_get(struct ns_common *ns)
 	VFS_WARN_ON_ONCE(is_initial_namespace(ns) && __ns_ref_active_read(ns) <= 0);
 }
 #define ns_ref_active_get(__ns) \
-	do { if (__ns) __ns_ref_active_get(to_ns_common(__ns)); } while (0)
+	do { \
+		if ((__ns) && !is_initial_namespace(&(__ns)->ns)) \
+			__ns_ref_active_get(to_ns_common(__ns)); \
+	} while (0)
 
 static __always_inline bool __ns_ref_active_get_not_zero(struct ns_common *ns)
 {
@@ -314,7 +317,10 @@ static __always_inline void __ns_ref_active_put(struct ns_common *ns)
 	}
 }
 #define ns_ref_active_put(__ns) \
-	do { if (__ns) __ns_ref_active_put(to_ns_common(__ns)); } while (0)
+	do { \
+		if ((__ns) && !is_initial_namespace(&(__ns)->ns)) \
+			__ns_ref_active_put(to_ns_common(__ns)); \
+	} while (0)
 
 static __always_inline struct ns_common *__must_check ns_get_unless_inactive(struct ns_common *ns)
 {
-- 
2.43.0