NFSD: Don't hold unrefcounted creds over call to nfsd_setuser()

nfsd_open() gets an unrefcounted pointer to the current process's effective
credentials at the top of the function, then calls nfsd_setuser() via
fh_verify() - which may replace and destroy the current process's effective
credentials - and then passes the unrefcounted pointer to dentry_open() - but
the credentials may have been destroyed by this point.

Instead, the value from current_cred() should be passed directly to
dentry_open() as one of its arguments, rather than being cached in a variable.

Possibly fh_verify() should return the creds to use.

This is a regression introduced by
745ca2475a6ac596e3d8d37c2759c0fbe2586227 "CRED: Pass credentials through
dentry_open()".

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-and-Verified-By: Steve Dickson <steved@redhat.com>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 4145083dcf88..23341c1063bc 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -678,7 +678,6 @@ __be32
 nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
                         int access, struct file **filp)
 {
-        const struct cred *cred = current_cred();
         struct dentry   *dentry;
         struct inode    *inode;
         int             flags = O_RDONLY|O_LARGEFILE;
@@ -733,7 +732,7 @@ nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
                 vfs_dq_init(inode);
         }
         *filp = dentry_open(dget(dentry), mntget(fhp->fh_export->ex_path.mnt),
-                            flags, cred);
+                            flags, current_cred());
         if (IS_ERR(*filp))
                 host_err = PTR_ERR(*filp);
         else