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Date: Wed, 7 Aug 2024 09:35:45 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Mathias Krause <minipli@grsecurity.net>
Cc: Masami Hiramatsu <mhiramat@kernel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@efficios.com>, Ajay Kaher <ajay.kaher@broadcom.com>,
 linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Ilkka
 =?UTF-8?B?TmF1bGFww6TDpA==?= <digirigawa@gmail.com>, Al Viro
 <viro@zeniv.linux.org.uk>, Brad Spengler <spender@grsecurity.net>
Subject: Re: [PATCH 2/2] tracefs: Don't overlay 'struct inode'
Message-ID: <20240807093545.4ec51d61@gandalf.local.home>
In-Reply-To: <20240807115143.45927-3-minipli@grsecurity.net>
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On Wed,  7 Aug 2024 13:51:39 +0200
Mathias Krause <minipli@grsecurity.net> wrote:

> diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
> index f704d8348357..a7769857962a 100644
> --- a/fs/tracefs/internal.h
> +++ b/fs/tracefs/internal.h
> @@ -10,10 +10,8 @@ enum {
>  };
>  
>  struct tracefs_inode {
> -	union {
> -		struct inode            vfs_inode;
> -		struct rcu_head		rcu;
> -	};
> +	struct inode		vfs_inode;
> +	struct rcu_head		rcu;

I rather not make this structure any bigger for the rcu element that is not
used until freed.

>  	/* The below gets initialized with memset_after(ti, 0, vfs_inode) */
>  	struct list_head	list;
>  	unsigned long           flags;

Perhaps:

diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index f704d8348357..ab6d6c3d835d 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -10,12 +10,12 @@ enum {
 };
 
 struct tracefs_inode {
+	struct inode            vfs_inode;
+	/* The below gets initialized with memset_after(ti, 0, vfs_inode) */
 	union {
-		struct inode            vfs_inode;
+		struct list_head	list;
 		struct rcu_head		rcu;
 	};
-	/* The below gets initialized with memset_after(ti, 0, vfs_inode) */
-	struct list_head	list;
 	unsigned long           flags;
 	void                    *private;
 };


-- Steve