linux-hardening - Re: [PATCH] netfs: Use container

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Date:   Wed, 18 May 2022 09:05:14 +0100
From:   David Howells <dhowells@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     dhowells@...hat.com, Jeff Layton <jlayton@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] netfs: Use container_of() for offset casting

I wonder if it would be worth making this explicit in the inode wrappers of
the users of netfslib.  In afs, for instance, there is:

	struct afs_vnode {
		struct {
			/* These must be contiguous */
			struct inode	vfs_inode;
			struct netfs_i_context netfs_ctx;
		};
		...
	};

would it be worth making that:

	struct afs_vnode {
		union {
			struct netfs_i_c_pair netfs_inode;
			struct {
				/* These must be contiguous */
				struct inode	vfs_inode;
				struct netfs_i_context netfs_ctx;
			};
		};
		...
	};

I don't want to do the following, say:


	struct afs_vnode {
		struct netfs_i_c_pair ni;
		...
	};

as that would then require a lot of s/->vfs_inode/->ni.vfs_inode/, but maybe
it would be better to include a struct inode in struct netfs_i_context, and
then do:

	struct afs_vnode {
		union {
			struct netfs_i_context netfs_ctx;
			struct inode vfs_inode;
		};
		...
	};

and perhaps rename netfs_i_context to netfs_inode (though that looks a bit
close to nfs_inode).  It's just a shame I can't do:

	struct netfs_inode : inode {
		...
	};

	struct afs_vnode : netfs_inode {
		...
	};

right? ;-)

On the other hand:

	warthog>git grep '[>.]vfs_inode' -- fs/{9p,afs,ceph,cifs,nfs} | wc -l
	181

so maybe a mass change to, say:

	struct netfs_inode {
		struct inode vfs_inode;
		...
	};

	struct afs_vnode {
		struct netfs_inode ni;
		...
	};

wouldn't be so bad.

David