linux-kernel - Re: [PATCH 01/18] vfs: add miscattr ops

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Date:   Thu, 25 Mar 2021 15:52:28 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Andreas Dilger <adilger@...ger.ca>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Dave Kleikamp <shaggy@...nel.org>,
        David Sterba <dsterba@...e.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Jan Kara <jack@...e.cz>,
        Joel Becker <jlbec@...lplan.org>,
        Matthew Garrett <matthew.garrett@...ula.com>,
        Mike Marshall <hubcap@...ibond.com>,
        Richard Weinberger <richard@....at>,
        Ryusuke Konishi <konishi.ryusuke@...il.com>,
        "Theodore Ts'o" <tytso@....edu>, Tyler Hicks <code@...icks.com>
Subject: Re: [PATCH 01/18] vfs: add miscattr ops

On Tue, Mar 23, 2021 at 1:24 AM Eric Biggers <ebiggers@...nel.org> wrote:

> > +int vfs_miscattr_set(struct dentry *dentry, struct miscattr *ma)
> > +{
> > +     struct inode *inode = d_inode(dentry);
> > +     struct miscattr old_ma = {};
> > +     int err;
> > +
> > +     if (d_is_special(dentry))
> > +             return -ENOTTY;
> > +
> > +     if (!inode->i_op->miscattr_set)
> > +             return -ENOIOCTLCMD;
> > +
> > +     if (!inode_owner_or_capable(inode))
> > +             return -EPERM;
>
> Shouldn't this be EACCES, not EPERM?

$ git diff master.. | grep -C1 inode_owner_or_capable | grep
"^-.*\(EPERM\|EACCES\)" | cut -d- -f3 | sort | uniq -c
     12 EACCES;
      4 EPERM;

So EACCES would win if this was a democracy.  However:

"[EACCES]
Permission denied. An attempt was made to access a file in a way
forbidden by its file access permissions."

"[EPERM]
Operation not permitted. An attempt was made to perform an operation
limited to processes with appropriate privileges or to the owner of a
file or other resource."

The EPERM description matches the semantics of
inode_owner_or_capable() exactly.  It's a pretty clear choice.

Thanks,
Miklos