[PATCH] nfsd: Fix NFSD_MAY_BYPASS_GSS and NFSD_MAY_BYPASS_GSS_ON_ROOT
From: Pali Rohár
Date: Thu Sep 12 2024 - 18:20:32 EST
Currently NFSD_MAY_BYPASS_GSS and NFSD_MAY_BYPASS_GSS_ON_ROOT do not bypass
only GSS, but bypass any authentication method. This is problem specially
for NFS3 AUTH_NULL-only exports.
The purpose of NFSD_MAY_BYPASS_GSS_ON_ROOT is described in RFC 2623,
section 2.3.2, to allow mounting NFS2/3 GSS-only export without
authentication. So few procedures which do not expose security risk used
during mount time can be called also with AUTH_NONE or AUTH_SYS, to allow
client mount operation to finish successfully.
The problem with current implementation is that for AUTH_NULL-only exports,
the NFSD_MAY_BYPASS_GSS_ON_ROOT is active also for NFS3 AUTH_UNIX mount
attempts which confuse NFS3 clients, and make them think that AUTH_UNIX is
enabled and is working. Linux NFS3 client never switches from AUTH_UNIX to
AUTH_NONE on active mount, which makes the mount inaccessible.
Fix the NFSD_MAY_BYPASS_GSS and NFSD_MAY_BYPASS_GSS_ON_ROOT implementation
and really allow to bypass only exports which have some GSS auth flavor
enabled.
The result would be: For AUTH_NULL-only export if client attempts to do
mount with AUTH_UNIX flavor then it will receive access errors, which
instruct client that AUTH_UNIX flavor is not usable and will either try
other auth flavor (AUTH_NULL if enabled) or fails mount procedure.
This should fix problems with AUTH_NULL-only or AUTH_UNIX-only exports if
client attempts to mount it with other auth flavor (e.g. with AUTH_NULL for
AUTH_UNIX-only export, or with AUTH_UNIX for AUTH_NULL-only export).
Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
---
fs/nfsd/export.c | 19 ++++++++++++++++++-
fs/nfsd/export.h | 2 +-
fs/nfsd/nfs4proc.c | 2 +-
fs/nfsd/nfs4xdr.c | 2 +-
fs/nfsd/nfsfh.c | 12 +++++++++---
fs/nfsd/vfs.c | 2 +-
6 files changed, 31 insertions(+), 8 deletions(-)
diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index 50b3135d07ac..eb11d3fdffe1 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -1074,7 +1074,7 @@ static struct svc_export *exp_find(struct cache_detail *cd,
return exp;
}
-__be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp)
+__be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp, bool may_bypass_gss)
{
struct exp_flavor_info *f, *end = exp->ex_flavors + exp->ex_nflavors;
struct svc_xprt *xprt = rqstp->rq_xprt;
@@ -1120,6 +1120,23 @@ __be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp)
if (nfsd4_spo_must_allow(rqstp))
return 0;
+ /* Some calls may be processed without authentication
+ * on GSS exports. For example NFS2/3 calls on root
+ * directory, see section 2.3.2 of rfc 2623.
+ * For "may_bypass_gss" check that export has really
+ * enabled some GSS flavor and also check that the
+ * used auth flavor is without auth (none or sys).
+ */
+ 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_GSS ||
+ f->pseudoflavor >= RPC_AUTH_GSS_KRB5)
+ return 0;
+ }
+ }
+
denied:
return rqstp->rq_vers < 4 ? nfserr_acces : nfserr_wrongsec;
}
diff --git a/fs/nfsd/export.h b/fs/nfsd/export.h
index ca9dc230ae3d..dc7cf4f6ac53 100644
--- a/fs/nfsd/export.h
+++ b/fs/nfsd/export.h
@@ -100,7 +100,7 @@ struct svc_expkey {
#define EX_WGATHER(exp) ((exp)->ex_flags & NFSEXP_GATHERED_WRITES)
int nfsexp_flags(struct svc_rqst *rqstp, struct svc_export *exp);
-__be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp);
+__be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp, bool may_bypass_gss);
/*
* Function declarations
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 2e39cf2e502a..0f67f4a7b8b2 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -2791,7 +2791,7 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
if (current_fh->fh_export &&
need_wrongsec_check(rqstp))
- op->status = check_nfsd_access(current_fh->fh_export, rqstp);
+ op->status = check_nfsd_access(current_fh->fh_export, rqstp, false);
}
encode_op:
if (op->status == nfserr_replay_me) {
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 97f583777972..b45ea5757652 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3775,7 +3775,7 @@ nfsd4_encode_entry4_fattr(struct nfsd4_readdir *cd, const char *name,
nfserr = nfserrno(err);
goto out_put;
}
- nfserr = check_nfsd_access(exp, cd->rd_rqstp);
+ nfserr = check_nfsd_access(exp, cd->rd_rqstp, false);
if (nfserr)
goto out_put;
diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index dd4e11a703aa..ed0eabfa3cb0 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -329,6 +329,7 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type, int access)
{
struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
struct svc_export *exp = NULL;
+ bool may_bypass_gss = false;
struct dentry *dentry;
__be32 error;
@@ -375,8 +376,13 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type, int access)
* which clients virtually always use auth_sys for,
* even while using RPCSEC_GSS for NFS.
*/
- if (access & NFSD_MAY_LOCK || access & NFSD_MAY_BYPASS_GSS)
+ if (access & NFSD_MAY_LOCK)
goto skip_pseudoflavor_check;
+ /*
+ * NFS4 PUTFH may bypass GSS (see nfsd4_putfh() in nfs4proc.c).
+ */
+ if (access & NFSD_MAY_BYPASS_GSS)
+ may_bypass_gss = true;
/*
* Clients may expect to be able to use auth_sys during mount,
* even if they use gss for everything else; see section 2.3.2
@@ -384,9 +390,9 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type, int access)
*/
if (access & NFSD_MAY_BYPASS_GSS_ON_ROOT
&& exp->ex_path.dentry == dentry)
- goto skip_pseudoflavor_check;
+ may_bypass_gss = true;
- error = check_nfsd_access(exp, rqstp);
+ error = check_nfsd_access(exp, rqstp, may_bypass_gss);
if (error)
goto out;
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 29b1f3613800..b2f5ea7c2187 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -320,7 +320,7 @@ nfsd_lookup(struct svc_rqst *rqstp, struct svc_fh *fhp, const char *name,
err = nfsd_lookup_dentry(rqstp, fhp, name, len, &exp, &dentry);
if (err)
return err;
- err = check_nfsd_access(exp, rqstp);
+ err = check_nfsd_access(exp, rqstp, false);
if (err)
goto out;
/*
--
2.20.1