linux-kernel - Re: [PATCH 1/3] VFS: introduce MAY_ACT_AS

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Message-ID: <28763.1538662213@warthog.procyon.org.uk>
Date:   Thu, 04 Oct 2018 15:10:13 +0100
From:   David Howells <dhowells@...hat.com>
To:     NeilBrown <neilb@...e.com>
Cc:     dhowells@...hat.com, "J. Bruce Fields" <bfields@...ldses.org>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Jan Harkes <jaharkes@...cmu.edu>, linux-nfs@...r.kernel.org,
        Miklos Szeredi <miklos@...redi.hu>,
        Jeff Layton <jlayton@...nel.org>, linux-kernel@...r.kernel.org,
        linux-afs@...ts.infradead.org, coda@...cmu.edu,
        linux-fsdevel@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 1/3] VFS: introduce MAY_ACT_AS_OWNER

NeilBrown <neilb@...e.com> wrote:

> diff --git a/fs/afs/security.c b/fs/afs/security.c
> index 81dfedb7879f..ac2e39de8bff 100644
> --- a/fs/afs/security.c
> +++ b/fs/afs/security.c
> @@ -349,6 +349,16 @@ int afs_permission(struct inode *inode, int mask)
>  	if (mask & MAY_NOT_BLOCK)
>  		return -ECHILD;
>  
> +	/* Short-circuit for owner */
> +	if (mask & MAY_ACT_AS_OWNER) {
> +		if (inode_owner_or_capable(inode))

You don't know that inode->i_uid in meaningful.  You may have noticed that
afs_permission() ignores i_uid and i_gid entirely.  It queries the server (if
this information is not otherwise cached) to ask what permits the user is
granted - where the user identity is defined by the key returned from
afs_request_key()[*].

So, NAK for the afs piece.

David

[*] If there's no appropriate key, anonymous permits will be used.