[PATCH] r/o bind mounts: get write access for vfs_rename() callers

This also uses the little helper in the NFS code to make an if() a little bit
less ugly.  We introduced the helper at the beginning of the series.

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 17 insertions, 4 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 00df735fb509..83c843b3fea3 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2718,8 +2718,12 @@ static int do_rename(int olddfd, const char *oldname,
         if (new_dentry == trap)
                 goto exit5;
 
+        error = mnt_want_write(oldnd.path.mnt);
+        if (error)
+                goto exit5;
         error = vfs_rename(old_dir->d_inode, old_dentry,
                                    new_dir->d_inode, new_dentry);
+        mnt_drop_write(oldnd.path.mnt);
 exit5:
         dput(new_dentry);
 exit4:
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 71f899482306..18a4cc9feeb3 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1710,13 +1710,20 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
         if (ndentry == trap)
                 goto out_dput_new;
 
-#ifdef MSNFS
-        if ((ffhp->fh_export->ex_flags & NFSEXP_MSNFS) &&
+        if (svc_msnfs(ffhp) &&
                 ((atomic_read(&odentry->d_count) > 1)
                  || (atomic_read(&ndentry->d_count) > 1))) {
                         host_err = -EPERM;
-        } else
-#endif
+                        goto out_dput_new;
+        }
+
+        host_err = -EXDEV;
+        if (ffhp->fh_export->ex_path.mnt != tfhp->fh_export->ex_path.mnt)
+                goto out_dput_new;
+        host_err = mnt_want_write(ffhp->fh_export->ex_path.mnt);
+        if (host_err)
+                goto out_dput_new;
+
         host_err = vfs_rename(fdir, odentry, tdir, ndentry);
         if (!host_err && EX_ISSYNC(tfhp->fh_export)) {
                 host_err = nfsd_sync_dir(tdentry);
@@ -1724,6 +1731,8 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
                         host_err = nfsd_sync_dir(fdentry);
         }
 
+        mnt_drop_write(ffhp->fh_export->ex_path.mnt);
+
  out_dput_new:
         dput(ndentry);
  out_dput_old: