ovl: verify upper dentry before unlink and rename

Unlink and rename in overlayfs checked the upper dentry for staleness by
verifying upper->d_parent against upperdir.  However the dentry can go
stale also by being unhashed, for example.

Expand the verification to actually look up the name again (under parent
lock) and check if it matches the upper dentry.  This matches what the VFS
does before passing the dentry to filesytem's unlink/rename methods, which
excludes any inconsistency caused by overlayfs.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Orabug: 24363418
CVE:CVE-2016-6198,CVE-2016-6197
Based on mainline v4.6 commit 11f3710417d026ea2f4fcf362d866342c5274185
Conflicts:
  fs/overlayfs/dir.c - code base
Signed-off-by: Chuck Anderson <chuck.anderson@oracle.com>

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 36d6a5b3229fd5ff535f158059286792a4712d09..c844ce3764bf9179c6024650dee40414a333d2e9 100644 (file)
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -596,21 +596,25 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
 {
        struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
        struct inode *dir = upperdir->d_inode;
-       struct dentry *upper = ovl_dentry_upper(dentry);
+       struct dentry *upper;
        int err;
 
        mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
+       upper = lookup_one_len(dentry->d_name.name, upperdir,
+                              dentry->d_name.len);
+       err = PTR_ERR(upper);
+       if (IS_ERR(upper))
+               goto out_unlock;
+
        err = -ESTALE;
-       if (upper->d_parent == upperdir) {
-               /* Don't let d_delete() think it can reset d_inode */
-               dget(upper);
+       if (upper == ovl_dentry_upper(dentry)) {
                if (is_dir)
                        err = vfs_rmdir(dir, upper);
                else
                        err = vfs_unlink(dir, upper, NULL);
-               dput(upper);
                ovl_dentry_version_inc(dentry->d_parent);
        }
+       dput(upper);
 
        /*
         * Keeping this dentry hashed would mean having to release
@@ -620,6 +624,7 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
         */
        if (!err)
                d_drop(dentry);
+out_unlock:
        mutex_unlock(&dir->i_mutex);
 
        return err;
@@ -840,29 +845,39 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
 
        trap = lock_rename(new_upperdir, old_upperdir);
 
-       olddentry = ovl_dentry_upper(old);
-       newdentry = ovl_dentry_upper(new);
-       if (newdentry) {
+
+       olddentry = lookup_one_len(old->d_name.name, old_upperdir,
+                                   old->d_name.len);
+       err = PTR_ERR(olddentry);
+       if (IS_ERR(olddentry))
+               goto out_unlock;
+
+       err = -ESTALE;
+       if (olddentry != ovl_dentry_upper(old))
+               goto out_dput_old;
+
+       newdentry = lookup_one_len(new->d_name.name, new_upperdir,
+                                   new->d_name.len);
+       err = PTR_ERR(newdentry);
+       if (IS_ERR(newdentry))
+               goto out_dput_old;
+
+       err = -ESTALE;
+       if (ovl_dentry_upper(new)) {
                if (opaquedir) {
-                       newdentry = opaquedir;
-                       opaquedir = NULL;
+                       if (newdentry != opaquedir)
+                               goto out_dput;
                } else {
-                       dget(newdentry);
+                       if (newdentry != ovl_dentry_upper(new))
+                               goto out_dput;
                }
        } else {
                new_create = true;
-               newdentry = lookup_one_len(new->d_name.name, new_upperdir,
-                                          new->d_name.len);
-               err = PTR_ERR(newdentry);
-               if (IS_ERR(newdentry))
-                       goto out_unlock;
+               if (!d_is_negative(newdentry) &&
+                   (!new_opaque || !ovl_is_whiteout(newdentry)))
+                       goto out_dput;
        }
 
-       err = -ESTALE;
-       if (olddentry->d_parent != old_upperdir)
-               goto out_dput;
-       if (newdentry->d_parent != new_upperdir)
-               goto out_dput;
        if (olddentry == trap)
                goto out_dput;
        if (newdentry == trap)
@@ -918,6 +933,8 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
 
 out_dput:
        dput(newdentry);
+out_dput_old:
+       dput(olddentry);
 out_unlock:
        unlock_rename(new_upperdir, old_upperdir);
 out_revert_creds: