ovl: simplify permission checking

The fact that we always do permission checking on the overlay inode and
clear MAY_WRITE for checking access to the lower inode allows cruft to be
removed from ovl_permission().

1) "default_permissions" option effectively did generic_permission() on the
overlay inode with i_mode, i_uid and i_gid updated from underlying
filesystem.  This is what we do by default now.  It did the update using
vfs_getattr() but that's only needed if the underlying filesystem can
change (which is not allowed).  We may later introduce a "paranoia_mode"
that verifies that mode/uid/gid are not changed.

2) splitting out the IS_RDONLY() check from inode_permission() also becomes
unnecessary once we remove the MAY_WRITE from the lower inode check.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

3 files changed, 1 insertions, 53 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 8f7dd547cfb3..66f42f5cf705 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -124,29 +124,6 @@ int ovl_permission(struct inode *inode, int mask)
         const struct cred *old_cred;
         int err;
 
-        if (ovl_is_default_permissions(inode)) {
-                struct kstat stat;
-                struct path realpath = { .dentry = realdentry };
-
-                if (mask & MAY_NOT_BLOCK)
-                        return -ECHILD;
-
-                realpath.mnt = ovl_entry_mnt_real(oe, inode, is_upper);
-
-                err = vfs_getattr(&realpath, &stat);
-                if (err)
-                        return err;
-
-                if ((stat.mode ^ inode->i_mode) & S_IFMT)
-                        return -ESTALE;
-
-                inode->i_mode = stat.mode;
-                inode->i_uid = stat.uid;
-                inode->i_gid = stat.gid;
-
-                return generic_permission(inode, mask);
-        }
-
         /* Careful in RCU walk mode */
         realinode = d_inode_rcu(realdentry);
         if (!realinode) {
@@ -154,27 +131,6 @@ int ovl_permission(struct inode *inode, int mask)
                 return -ENOENT;
         }
 
-        if (mask & MAY_WRITE) {
-                umode_t mode = realinode->i_mode;
-
-                /*
-                 * Writes will always be redirected to upper layer, so
-                 * ignore lower layer being read-only.
-                 *
-                 * If the overlay itself is read-only then proceed
-                 * with the permission check, don't return EROFS.
-                 * This will only happen if this is the lower layer of
-                 * another overlayfs.
-                 *
-                 * If upper fs becomes read-only after the overlay was
-                 * constructed return EROFS to prevent modification of
-                 * upper layer.
-                 */
-                if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
-                    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
-                        return -EROFS;
-        }
-
         /*
          * Check overlay inode with the creds of task and underlying inode
          * with creds of mounter
@@ -186,7 +142,7 @@ int ovl_permission(struct inode *inode, int mask)
         old_cred = ovl_override_creds(inode->i_sb);
         if (!is_upper)
                 mask &= ~(MAY_WRITE | MAY_APPEND);
-        err = __inode_permission(realinode, mask);
+        err = inode_permission(realinode, mask);
         revert_creds(old_cred);
 
         return err;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 75128c70aa6a..e8d50da384d5 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -146,7 +146,6 @@ struct inode *ovl_inode_real(struct inode *inode);
 struct vfsmount *ovl_entry_mnt_real(struct ovl_entry *oe, struct inode *inode,
                                     bool is_upper);
 struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry);
-bool ovl_is_default_permissions(struct inode *inode);
 void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache);
 struct dentry *ovl_workdir(struct dentry *dentry);
 int ovl_want_write(struct dentry *dentry);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 893d6e0ea1c5..80598912a5d9 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -185,13 +185,6 @@ struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
         return oe->cache;
 }
 
-bool ovl_is_default_permissions(struct inode *inode)
-{
-        struct ovl_fs *ofs = inode->i_sb->s_fs_info;
-
-        return ofs->config.default_permissions;
-}
-
 void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
 {
         struct ovl_entry *oe = dentry->d_fsdata;