linux-kernel - [PATCH] pidfs: detect refcount bugs

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Message-ID: <20250506-uferbereich-guttun-7c8b1a0a431f@brauner>
Date: Tue,  6 May 2025 13:55:54 +0200
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] pidfs: detect refcount bugs

Now that we have pidfs_{get,register}_pid() that needs to be paired with
pidfs_put_pid() it's possible that someone pairs them with put_pid().
Thus freeing struct pid while it's still used by pidfs. Notice when that
happens. I'll also add a scheme to detect invalid uses of
pidfs_get_pid() and pidfs_put_pid() later.

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 kernel/pid.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/pid.c b/kernel/pid.c
index 26f1e136f017..8317bcbc7cf7 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -100,6 +100,7 @@ void put_pid(struct pid *pid)
 
 	ns = pid->numbers[pid->level].ns;
 	if (refcount_dec_and_test(&pid->count)) {
+		WARN_ON_ONCE(pid->stashed);
 		kmem_cache_free(ns->pid_cachep, pid);
 		put_pid_ns(ns);
 	}
-- 
2.47.2