Re: [for-linus][PATCH 1/3] eventfs: Have the inodes all for files and directories all be the same

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Kees Cook <keescook@chromium.org>,
	 linux-kernel@vger.kernel.org,
	Masami Hiramatsu <mhiramat@kernel.org>,
	 Mark Rutland <mark.rutland@arm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	 Andrew Morton <akpm@linux-foundation.org>,
	Christian Brauner <brauner@kernel.org>,
	 Al Viro <viro@zeniv.linux.org.uk>,
	Ajay Kaher <ajay.kaher@broadcom.com>
Subject: Re: [for-linus][PATCH 1/3] eventfs: Have the inodes all for files and directories all be the same
Date: Mon, 22 Jan 2024 10:19:12 -0800	[thread overview]
Message-ID: <CAHk-=wiLqJYT2GGSBhKuJS-Uq1DVq3S32oP0SwqQiATuBivxcg@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wjGxVVKvxVf=NDnMhB3=eQ_NMiEY3onG1wRAjJepig=aw@mail.gmail.com>

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On Mon, 22 Jan 2024 at 09:39, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Actually, why not juist add an inode number to your data structures,
> at least for directories? And just do a static increment on it as they
> get registered?
>
> That avoids the whole issue with possibly leaking kernel address data.

The 'nlink = 1' thing doesn't seem to make 'find' any happier for this
case, sadly.

But the inode number in the 'struct eventfs_inode' looks trivial. And
doesn't even grow that structure on 64-bit architectures at least,
because the struct is already 64-bit aligned, and had only one 32-bit
entry at the end.

On 32-bit architectures the structure size grows, but I'm not sure the
allocation size grows. Our kmalloc() is quantized at odd numbers.

IOW, this trivial patch seems to be much safer than worrying about
some pointer exposure.

              Linus

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 fs/tracefs/event_inode.c | 6 ++++--
 fs/tracefs/internal.h    | 1 +
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 6795fda2af19..0b52ec111cf3 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -395,8 +395,7 @@ static struct dentry *create_dir(struct eventfs_inode *ei, struct dentry *parent
 	inode->i_op = &eventfs_root_dir_inode_operations;
 	inode->i_fop = &eventfs_file_operations;
 
-	/* All directories will have the same inode number */
-	inode->i_ino = EVENTFS_DIR_INODE_INO;
+	inode->i_ino = ei->ino;
 
 	ti = get_tracefs(inode);
 	ti->flags |= TRACEFS_EVENT_INODE;
@@ -859,6 +858,7 @@ struct eventfs_inode *eventfs_create_dir(const char *name, struct eventfs_inode
 					 int size, void *data)
 {
 	struct eventfs_inode *ei;
+	static int ino_counter = EVENTFS_DIR_INODE_INO;
 
 	if (!parent)
 		return ERR_PTR(-EINVAL);
@@ -889,6 +889,8 @@ struct eventfs_inode *eventfs_create_dir(const char *name, struct eventfs_inode
 	INIT_LIST_HEAD(&ei->list);
 
 	mutex_lock(&eventfs_mutex);
+	ei->ino = ++ino_counter;
+
 	if (!parent->is_freed) {
 		list_add_tail(&ei->list, &parent->children);
 		ei->d_parent = parent->dentry;
diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index 12b7d0150ae9..1a574d306ea9 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -64,6 +64,7 @@ struct eventfs_inode {
 		struct llist_node	llist;
 		struct rcu_head		rcu;
 	};
+	unsigned int			ino;
 	unsigned int			is_freed:1;
 	unsigned int			is_events:1;
 	unsigned int			nr_entries:30;
