On Thu, Oct 10, 2024 at 07:14:07AM +1100, NeilBrown wrote:
> On Thu, 10 Oct 2024, Chuck Lever wrote:
> > On Tue, Oct 08, 2024 at 05:47:55PM -0400, NeilBrown wrote:
> > > And NFSD_MAY_LOCK should be discarded, and nlm_fopen() should set
> > > NFSD_MAY_BYPASS_SEC.
> >
> > 366 /*
> > 367 * pseudoflavor restrictions are not enforced on NLM,
> >
> > Wrt the mention of "NLM", nfsd4_lock() also sets NFSD_MAY_LOCK.
>
> True, but it shouldn't. NFSD_MAY_LOCK is only used to bypass the GSS
> requirement. It must have been copied into nfsd4_lock() without a full
> understanding of its purpose.
nfsd4_lock()'s use of MAY_LOCK goes back before the git era, so it's
difficult to say with certainty.
I would like to keep such subtle changes bisectable. To me, it seems
like it would be a basic first step to change the fh_verify() call
in nfsd4_lock() to use (NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE)
instead of NFSD_MAY_LOCK, as a separate patch.
> > 368 * which clients virtually always use auth_sys for,
> > 369 * even while using RPCSEC_GSS for NFS.
> > 370 */
> > 371 if (access & NFSD_MAY_LOCK)
> > 372 goto skip_pseudoflavor_check;
> > 373 if (access & NFSD_MAY_BYPASS_GSS)
> > 374 may_bypass_gss = true;
> > 375 /*
> > 376 * Clients may expect to be able to use auth_sys during mount,
> > 377 * even if they use gss for everything else; see section 2.3.2
> > 378 * of rfc 2623.
> > 379 */
> > 380 if (access & NFSD_MAY_BYPASS_GSS_ON_ROOT
> > 381 && exp->ex_path.dentry == dentry)
> > 382 may_bypass_gss = true;
> > 383
> > 384 error = check_nfsd_access(exp, rqstp, may_bypass_gss);
> > 385 if (error)
> > 386 goto out;
> > 387
> > 388 skip_pseudoflavor_check:
> > 389 /* Finally, check access permissions. */
> > 390 error = nfsd_permission(cred, exp, dentry, access);
> >
> > MAY_LOCK is checked in nfsd_permission() and __fh_verify().
> >
> > But MAY_BYPASS_GSS is set in loads of places that use those two
> > functions. How can we be certain that the two flags are equivalent?
>
> We can be certain by looking at the effect. Before a recent patch they
> both did "goto skip_pseudoflavor_check" and nothing else.
I'm still not convinced MAY_LOCK and MAY_BYPASS_GSS are 100%
equivalent. nfsd_permission() checks for MAY_LOCK, but does not
check for MAY_BYPASS_GSS:
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 only consumer of MAY_BYPASS_GSS seems to be OP_PUTFH, now that
I'm looking closely for it. But I don't think we want the
no_auth_nlm export option to modify the way PUTFH behaves.
--
Chuck Lever
