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Message-id: <169100930100.32308.6829680445843128900@noble.neil.brown.name>
Date: Thu, 03 Aug 2023 06:48:21 +1000
From: "NeilBrown" <neilb@...e.de>
To: "Jeff Layton" <jlayton@...nel.org>
Cc: "Chuck Lever" <chuck.lever@...cle.com>,
"Olga Kornievskaia" <kolga@...app.com>,
"Dai Ngo" <Dai.Ngo@...cle.com>, "Tom Talpey" <tom@...pey.com>,
linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
"Jeff Layton" <jlayton@...nel.org>
Subject: Re: [PATCH v3] nfsd: don't hand out write delegations on O_WRONLY opens
On Thu, 03 Aug 2023, Jeff Layton wrote:
> I noticed that xfstests generic/001 was failing against linux-next nfsd.
>
> The client would request a OPEN4_SHARE_ACCESS_WRITE open, and the server
> would hand out a write delegation. The client would then try to use that
> write delegation as the source stateid in a COPY or CLONE operation, and
> the server would respond with NFS4ERR_STALE.
>
> The problem is that the struct file associated with the delegation does
> not necessarily have read permissions. It's handing out a write
> delegation on what is effectively an O_WRONLY open. RFC 8881 states:
>
> "An OPEN_DELEGATE_WRITE delegation allows the client to handle, on its
> own, all opens."
>
> Given that the client didn't request any read permissions, and that nfsd
> didn't check for any, it seems wrong to give out a write delegation.
>
> Only hand out a write delegation if we have a O_RDWR descriptor
> available. If it fails to find an appropriate write descriptor, go
> ahead and try for a read delegation if NFS4_SHARE_ACCESS_READ was
> requested.
>
> This fixes xfstest generic/001.
>
> Closes: https://bugzilla.linux-nfs.org/show_bug.cgi?id=412
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
> Changes in v3:
> - add find_rw_file helper to ensure spinlock is taken appropriately
> - refine comments over conditionals
> - Link to v2: https://lore.kernel.org/r/20230801-wdeleg-v2-1-20c14252bab4@kernel.org
>
> Changes in v2:
> - Rework the logic when finding struct file for the delegation. The
> earlier patch might still have attached a O_WRONLY file to the deleg
> in some cases, and could still have handed out a write delegation on
> an O_WRONLY OPEN request in some cases.
> ---
> fs/nfsd/nfs4state.c | 48 +++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 37 insertions(+), 11 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index ef7118ebee00..c551784d108a 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -649,6 +649,18 @@ find_readable_file(struct nfs4_file *f)
> return ret;
> }
>
> +static struct nfsd_file *
> +find_rw_file(struct nfs4_file *f)
> +{
> + struct nfsd_file *ret;
> +
> + spin_lock(&f->fi_lock);
> + ret = nfsd_file_get(f->fi_fds[O_RDWR]);
> + spin_unlock(&f->fi_lock);
> +
> + return ret;
> +}
> +
> struct nfsd_file *
> find_any_file(struct nfs4_file *f)
> {
> @@ -5449,7 +5461,7 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> struct nfs4_file *fp = stp->st_stid.sc_file;
> struct nfs4_clnt_odstate *odstate = stp->st_clnt_odstate;
> struct nfs4_delegation *dp;
> - struct nfsd_file *nf;
> + struct nfsd_file *nf = NULL;
> struct file_lock *fl;
> u32 dl_type;
>
> @@ -5461,21 +5473,35 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> if (fp->fi_had_conflict)
> return ERR_PTR(-EAGAIN);
>
> - if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
> - nf = find_writeable_file(fp);
> + /*
> + * Try for a write delegation first. RFC8881 section 10.4 says:
> + *
> + * "An OPEN_DELEGATE_WRITE delegation allows the client to handle,
> + * on its own, all opens."
> + *
> + * Furthermore the client can use a write delegationf or most read
> + * operations as well, so we require a O_RDWR file here.
> + *
> + * Only a write delegation in the case of a BOTH open, and ensure
> + * we get the O_RDWR descriptor.
> + */
This comment isn't working for me, and it isn't just the need for
s/f / f/
Neither the "Furthermore" or the "Only a" seem to make sense.
I think the key take away from the RFC quote is "all opens" and that
implies "opens for read". i.e. all delegations imply read access.
So I would then start the code with
if (!(open->op_share_access & NFS4_SHARE_ACCESS_READ))
return ERR_PTR(-EACCES);
then choose between readable and rw.
So the comment would say:
* RFC8881 section 10.4 says:
*
* "An OPEN_DELEGATE_READ delegation allows a client to handle,
* on its own, requests to open a file for reading ...."
* and
* "An OPEN_DELEGATE_WRITE delegation allows the client to handle,
* on its own, all opens."
* and as "all" includes "for reading", any delegation must
* allow reading. So if the original access is write-only we
* do not return a delegation, otherwise we require at least
* "readable", to return a DELGATE_READ and "rw" to return
* DELEGATE_WRITE which we only try if the original open
* requested write access.
Code looks good, though I find the growth of find_foo_file APIs
aesthetically unpleasant.
NeilBrown
> + if ((open->op_share_access & NFS4_SHARE_ACCESS_BOTH) == NFS4_SHARE_ACCESS_BOTH) {
> + nf = find_rw_file(fp);
> dl_type = NFS4_OPEN_DELEGATE_WRITE;
> - } else {
> + }
> +
> + /*
> + * If the file is being opened O_RDONLY or we couldn't get a O_RDWR
> + * file for some reason, then try for a read deleg instead.
> + */
> + if (!nf && (open->op_share_access & NFS4_SHARE_ACCESS_READ)) {
> nf = find_readable_file(fp);
> dl_type = NFS4_OPEN_DELEGATE_READ;
> }
> - if (!nf) {
> - /*
> - * We probably could attempt another open and get a read
> - * delegation, but for now, don't bother until the
> - * client actually sends us one.
> - */
> +
> + if (!nf)
> return ERR_PTR(-EAGAIN);
> - }
> +
> spin_lock(&state_lock);
> spin_lock(&fp->fi_lock);
> if (nfs4_delegation_exists(clp, fp))
>
> ---
> base-commit: a734662572708cf062e974f659ae50c24fc1ad17
> change-id: 20230731-wdeleg-bbdb6b25a3c6
>
> Best regards,
> --
> Jeff Layton <jlayton@...nel.org>
>
>
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