nfsd: fix unlikely NULL deref in mach_creds_match

We really shouldn't allow a client to be created with cl_mach_cred set
unless it also has a principal name.

This also allows us to fail such cases immediately on EXCHANGE_ID as
opposed to waiting and incorrectly returning WRONG_CRED on the following
CREATE_SESSION.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index efa3d4c09dab..ed58ced6fa8b 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2385,6 +2385,15 @@ nfsd4_exchange_id(struct svc_rqst *rqstp,
                         status = nfserr_inval;
                         goto out_nolock;
                 }
+                /*
+                 * Sometimes userspace doesn't give us a principal.
+                 * Which is a bug, really.  Anyway, we can't enforce
+                 * MACH_CRED in that case, better to give up now:
+                 */
+                if (!new->cl_cred.cr_principal) {
+                        status = nfserr_serverfault;
+                        goto out_nolock;
+                }
                 new->cl_mach_cred = true;
         case SP4_NONE:
                 break;