nfsd: fix EXDEV checking in rename

We again check for the EXDEV a little later on, so the first check is
redundant.  This check is also slightly racier, since a badly timed
eviction from the export cache could leave us with the two fh_export
pointers pointing to two different cache entries which each refer to the
same underlying export.

It's better to compare vfsmounts as the later check does, but that
leaves a minor security hole in the case where the two exports refer to
two different directories especially if (for example) they have
different root-squashing options.

So, compare ex_path.dentry too.

Reported-by: Joe Habermann <joe.habermann@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 2 insertions, 4 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 2b2e2396a869..84ce601d8063 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1758,10 +1758,6 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
         tdentry = tfhp->fh_dentry;
         tdir = tdentry->d_inode;
 
-        err = (rqstp->rq_vers == 2) ? nfserr_acces : nfserr_xdev;
-        if (ffhp->fh_export != tfhp->fh_export)
-                goto out;
-
         err = nfserr_perm;
         if (!flen || isdotent(fname, flen) || !tlen || isdotent(tname, tlen))
                 goto out;
@@ -1802,6 +1798,8 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
         host_err = -EXDEV;
         if (ffhp->fh_export->ex_path.mnt != tfhp->fh_export->ex_path.mnt)
                 goto out_dput_new;
+        if (ffhp->fh_export->ex_path.dentry != tfhp->fh_export->ex_path.dentry)
+                goto out_dput_new;
 
         host_err = nfsd_break_lease(odentry->d_inode);
         if (host_err)