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Date: Thu, 4 Jan 2024 09:27:12 -0500
From: Chuck Lever <chuck.lever@oracle.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Chuck Lever <cel@kernel.org>, jlayton@redhat.com,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Jeff Layton <jlayton@kernel.org>, linux-fsdevel@vger.kernel.org,
        linux-nfs@vger.kernel.org, trondmy@hammerspace.com,
        viro@zeniv.linux.org.uk, brauner@kernel.org
Subject: Re: [PATCH v2 1/2] exportfs: fix the fallback implementation of the
 get_name export operation
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On Thu, Jan 04, 2024 at 09:39:04AM +0200, Amir Goldstein wrote:
> On Wed, Jan 3, 2024 at 5:19 PM Chuck Lever <cel@kernel.org> wrote:
> >
> > From: Trond Myklebust <trond.myklebust@hammerspace.com>
> >
> > The fallback implementation for the get_name export operation uses
> > readdir() to try to match the inode number to a filename. That filename
> > is then used together with lookup_one() to produce a dentry.
> > A problem arises when we match the '.' or '..' entries, since that
> > causes lookup_one() to fail. This has sometimes been seen to occur for
> > filesystems that violate POSIX requirements around uniqueness of inode
> > numbers, something that is common for snapshot directories.
> >
> > This patch just ensures that we skip '.' and '..' rather than allowing a
> > match.
> >
> > Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> > Reviewed-by: Jeff Layton <jlayton@kernel.org>
> > Acked-by: Amir Goldstein <amir73il@gmail.com>
> > Link: https://lore.kernel.org/linux-nfs/CAOQ4uxiOZobN76OKB-VBNXWeFKVwLW_eK5QtthGyYzWU9mjb7Q@mail.gmail.com/
> > Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> > ---
> >  fs/exportfs/expfs.c |    4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
> > index 3ae0154c5680..84af58eaf2ca 100644
> > --- a/fs/exportfs/expfs.c
> > +++ b/fs/exportfs/expfs.c
> > @@ -255,7 +255,9 @@ static bool filldir_one(struct dir_context *ctx, const char *name, int len,
> >                 container_of(ctx, struct getdents_callback, ctx);
> >
> >         buf->sequence++;
> > -       if (buf->ino == ino && len <= NAME_MAX) {
> > +       /* Ignore the '.' and '..' entries */
> > +       if ((len > 2 || name[0] != '.' || (len == 2 && name[1] != '.')) &&
> > +           buf->ino == ino && len <= NAME_MAX) {
> 
> 
> Thank you for creating the helper, but if you already went to this trouble,
> I think it is better to introduce is_dot_dotdot() as a local helper already
> in this backportable patch, so that stable kernel code is same as upstream
> code (good for future fixes) and then dedupe the local helper with the rest
> of the local helpers in patch 2?

There's now no Fixes: nor a Cc: stable on 1/2. You convinced me that
1/2 will not result in any external behavior change.

The upshot is I do not expect 1/2 will be backported, unless I have
grossly misread your emails.


-- 
Chuck Lever