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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Wed, 17 Aug 2022 18:32:15 -0400
Message-ID: <CAN-5tyFvV7QOxyAQXu3UM5swQVB2roDpQ5CBRVc64Epp1gj9hg@mail.gmail.com>
Subject: Re: [RFC] problems with alloc_file_pseudo() use in __nfs42_ssc_open()
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>,
        Olga Kornievskaia <kolga@netapp.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Wed, Aug 17, 2022 at 6:18 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
>         My apologies for having missed that back when the SSC
> patchset had been done (and missing the problems after it got
> merged, actually).
>
> 1) if this
>         r_ino = nfs_fhget(ss_mnt->mnt_sb, src_fh, fattr);
> in __nfs42_ssc_open() yields a directory inode, we are screwed
> as soon as it's passed to alloc_file_pseudo() - a *lot* of places
> in dcache handling would break if we do that.  It's not too
> nice for a regular file from non-cooperating filesystem, but for
> directory ones it's deadly.

This inode is created to make an appearance of an opened file to do
(an NFS) read, it's never a directory.

> 2) if alloc_file_pseudo() fails there, we get an inode leak.  It
> needs an iput() for that case.  As in
>         if (IS_ERR(filep)) {
>                 res = ERR_CAST(filep);
>                 iput(r_ino);
>                 goto out_free_name;
>         }
>
> But I'd like to point out that alloc_file_pseudo() is not inteded for
> use on normal filesystem's inodes - the use here *mostly* works
> (directories aside), but...  Use it on filesystem with non-trivial
> default dentry_operations and things will get interesting, etc.