Re: [PATCH v2] nfsd: refine and rename NFSD_MAY_LOCK

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On Wed, 12 Mar 2025, Olga Kornievskaia wrote:
> On Tue, Mar 11, 2025 at 11:28 AM Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
> >
> > On Thu, Oct 17, 2024 at 5:42 PM NeilBrown <neilb@xxxxxxx> wrote:
> > >
> > >
> > > NFSD_MAY_LOCK means a few different things.
> > > - it means that GSS is not required.
> > > - it means that with NFSEXP_NOAUTHNLM, authentication is not required
> > > - it means that OWNER_OVERRIDE is allowed.
> > >
> > > None of these are specific to locking, they are specific to the NLM
> > > protocol.
> > > So:
> > >  - rename to NFSD_MAY_NLM
> > >  - set NFSD_MAY_OWNER_OVERRIDE and NFSD_MAY_BYPASS_GSS in nlm_fopen()
> > >    so that NFSD_MAY_NLM doesn't need to imply these.
> > >  - move the test on NFSEXP_NOAUTHNLM out of nfsd_permission() and
> > >    into fh_verify where other special-case tests on the MAY flags
> > >    happen.  nfsd_permission() can be called from other places than
> > >    fh_verify(), but none of these will have NFSD_MAY_NLM.
> >
> > This patch breaks NLM when used in combination with TLS.
> 
> I was too quick to link this to TLS. It's presence of security policy
> so sec=krb* causes the same problems.
> 
> >  If exports
> > have xprtsec=tls:mtls and mount is done with tls/mtls, the server
> > won't give any locks and client will get "no locks available" error.
> >
> > >
> > > Signed-off-by: NeilBrown <neilb@xxxxxxx>
> > > ---
> > >
> > > No change from previous patch - the corruption in the email has been
> > > avoided (I hope).
> > >
> > >
> > >  fs/nfsd/lockd.c | 13 +++++++++++--
> > >  fs/nfsd/nfsfh.c | 12 ++++--------
> > >  fs/nfsd/trace.h |  2 +-
> > >  fs/nfsd/vfs.c   | 12 +-----------
> > >  fs/nfsd/vfs.h   |  2 +-
> > >  5 files changed, 18 insertions(+), 23 deletions(-)
> > >
> > > diff --git a/fs/nfsd/lockd.c b/fs/nfsd/lockd.c
> > > index 46a7f9b813e5..edc9f75dc75c 100644
> > > --- a/fs/nfsd/lockd.c
> > > +++ b/fs/nfsd/lockd.c
> > > @@ -38,11 +38,20 @@ nlm_fopen(struct svc_rqst *rqstp, struct nfs_fh *f, struct file **filp,
> > >         memcpy(&fh.fh_handle.fh_raw, f->data, f->size);
> > >         fh.fh_export = NULL;
> > >
> > > +       /*
> > > +        * Allow BYPASS_GSS as some client implementations use AUTH_SYS
> > > +        * for NLM even when GSS is used for NFS.
> > > +        * Allow OWNER_OVERRIDE as permission might have been changed
> > > +        * after the file was opened.
> > > +        * Pass MAY_NLM so that authentication can be completely bypassed
> > > +        * if NFSEXP_NOAUTHNLM is set.  Some older clients use AUTH_NULL
> > > +        * for NLM requests.
> > > +        */
> > >         access = (mode == O_WRONLY) ? NFSD_MAY_WRITE : NFSD_MAY_READ;
> > > -       access |= NFSD_MAY_LOCK;
> > > +       access |= NFSD_MAY_NLM | NFSD_MAY_OWNER_OVERRIDE | NFSD_MAY_BYPASS_GSS;
> > >         nfserr = nfsd_open(rqstp, &fh, S_IFREG, access, filp);
> > >         fh_put(&fh);
> > > -       /* We return nlm error codes as nlm doesn't know
> > > +       /* We return nlm error codes as nlm doesn't know
> > >          * about nfsd, but nfsd does know about nlm..
> > >          */
> > >         switch (nfserr) {
> > > diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> > > index 40533f7c7297..6a831cb242df 100644
> > > --- a/fs/nfsd/nfsfh.c
> > > +++ b/fs/nfsd/nfsfh.c
> > > @@ -363,13 +363,10 @@ __fh_verify(struct svc_rqst *rqstp,
> > >         if (error)
> > >                 goto out;
> > >
> > > -       /*
> > > -        * pseudoflavor restrictions are not enforced on NLM,
> > > -        * which clients virtually always use auth_sys for,
> > > -        * even while using RPCSEC_GSS for NFS.
> > > -        */
> > > -       if (access & NFSD_MAY_LOCK)
> > > -               goto skip_pseudoflavor_check;
> > > +       if ((access & NFSD_MAY_NLM) && (exp->ex_flags & NFSEXP_NOAUTHNLM))
> 
> I think this should either be an OR or the fact that "nlm but only
> with insecurelock export option and not other" is the only way to
> bypass checking is wrong. I think it's just a check for NLM that
> stays.

I don't think that NLM gets a complete bypass unless no_auth_nlm is set.
For the case you are describing, I think NFSD_MAY_BYPASS_GSS is supposed
to make it work.

I assume the NLM request is arriving with AUTH_SYS authentication?
So check_nfsd_access() is being called with may_bypass_gss and this:

	if (may_bypass_gss && (
	     rqstp->rq_cred.cr_flavor == RPC_AUTH_NULL ||
	     rqstp->rq_cred.cr_flavor == RPC_AUTH_UNIX)) {
		for (f = exp->ex_flavors; f < end; f++) {
			if (f->pseudoflavor >= RPC_AUTH_DES)
				return 0;
		}
	}

in check_nfsd_access() should succeed.
Can you add some tracing and see what is happening in here?
Maybe the "goto denied" earlier in the function is being reached.  I
don't fully understand the TLS code yet - maybe it needs some test on
may_bypass_gss. 

Thanks,
NeilBrown


> 
> > > +               /* NLM is allowed to fully bypass authentication */
> > > +               goto out;
> > > +
> > >         if (access & NFSD_MAY_BYPASS_GSS)
> > >                 may_bypass_gss = true;
> > >         /*
> > > @@ -385,7 +382,6 @@ __fh_verify(struct svc_rqst *rqstp,
> > >         if (error)
> > >                 goto out;
> > >
> > > -skip_pseudoflavor_check:
> > >         /* Finally, check access permissions. */
> > >         error = nfsd_permission(cred, exp, dentry, access);
> > >  out:
> > > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> > > index b8470d4cbe99..3448e444d410 100644
> > > --- a/fs/nfsd/trace.h
> > > +++ b/fs/nfsd/trace.h
> > > @@ -79,7 +79,7 @@ DEFINE_NFSD_XDR_ERR_EVENT(cant_encode);
> > >                 { NFSD_MAY_READ,                "READ" },               \
> > >                 { NFSD_MAY_SATTR,               "SATTR" },              \
> > >                 { NFSD_MAY_TRUNC,               "TRUNC" },              \
> > > -               { NFSD_MAY_LOCK,                "LOCK" },               \
> > > +               { NFSD_MAY_NLM,                 "NLM" },                \
> > >                 { NFSD_MAY_OWNER_OVERRIDE,      "OWNER_OVERRIDE" },     \
> > >                 { NFSD_MAY_LOCAL_ACCESS,        "LOCAL_ACCESS" },       \
> > >                 { NFSD_MAY_BYPASS_GSS_ON_ROOT,  "BYPASS_GSS_ON_ROOT" }, \
> > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > > index 51f5a0b181f9..2610638f4301 100644
> > > --- a/fs/nfsd/vfs.c
> > > +++ b/fs/nfsd/vfs.c
> > > @@ -2509,7 +2509,7 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
> > >                 (acc & NFSD_MAY_EXEC)?  " exec"  : "",
> > >                 (acc & NFSD_MAY_SATTR)? " sattr" : "",
> > >                 (acc & NFSD_MAY_TRUNC)? " trunc" : "",
> > > -               (acc & NFSD_MAY_LOCK)?  " lock"  : "",
> > > +               (acc & NFSD_MAY_NLM)?   " nlm"  : "",
> > >                 (acc & NFSD_MAY_OWNER_OVERRIDE)? " owneroverride" : "",
> > >                 inode->i_mode,
> > >                 IS_IMMUTABLE(inode)?    " immut" : "",
> > > @@ -2534,16 +2534,6 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp,
> > >         if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode))
> > >                 return nfserr_perm;
> > >
> > > -       if (acc & NFSD_MAY_LOCK) {
> > > -               /* If we cannot rely on authentication in NLM requests,
> > > -                * just allow locks, otherwise require read permission, or
> > > -                * ownership
> > > -                */
> > > -               if (exp->ex_flags & NFSEXP_NOAUTHNLM)
> > > -                       return 0;
> > > -               else
> > > -                       acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE;
> > > -       }
> > >         /*
> > >          * The file owner always gets access permission for accesses that
> > >          * would normally be checked at open time. This is to make
> > > diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> > > index 854fb95dfdca..f9b09b842856 100644
> > > --- a/fs/nfsd/vfs.h
> > > +++ b/fs/nfsd/vfs.h
> > > @@ -20,7 +20,7 @@
> > >  #define NFSD_MAY_READ                  0x004 /* == MAY_READ */
> > >  #define NFSD_MAY_SATTR                 0x008
> > >  #define NFSD_MAY_TRUNC                 0x010
> > > -#define NFSD_MAY_LOCK                  0x020
> > > +#define NFSD_MAY_NLM                   0x020 /* request is from lockd */
> > >  #define NFSD_MAY_MASK                  0x03f
> > >
> > >  /* extra hints to permission and open routines: */
> > >
> > > base-commit: c4e418a53fe30d8e1da68f5aabca352b682fd331
> > > --
> > > 2.46.0
> > >
> > >
> 





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