ovl: lookup indexed ancestor of lower dir

ovl_lookup_real() in lower layer walks back lower parents to find the
topmost indexed parent. If an indexed ancestor is found before reaching
lower layer root, ovl_lookup_real() is called recursively with upper
layer to walk back from indexed upper to the topmost connected/hashed
upper parent (or up to root).

ovl_lookup_real() in upper layer then walks forward to connect the topmost
upper overlay dir dentry and ovl_lookup_real() in lower layer continues to
walk forward to connect the decoded lower overlay dir dentry.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

3 files changed, 56 insertions, 7 deletions

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index 092e6e8c9258..b65ea49de457 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -294,6 +294,10 @@ fail:
         goto out;
 }
 
+static struct dentry *ovl_lookup_real(struct super_block *sb,
+                                      struct dentry *real,
+                                      struct ovl_layer *layer);
+
 /*
  * Lookup an indexed or hashed overlay dentry by real inode.
  */
@@ -301,9 +305,16 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
                                             struct dentry *real,
                                             struct ovl_layer *layer)
 {
+        struct ovl_fs *ofs = sb->s_fs_info;
+        struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt };
+        struct dentry *index = NULL;
         struct dentry *this = NULL;
         struct inode *inode;
 
+        /*
+         * Decoding upper dir from index is expensive, so first try to lookup
+         * overlay dentry in inode/dcache.
+         */
         inode = ovl_lookup_inode(sb, real, !layer->idx);
         if (IS_ERR(inode))
                 return ERR_CAST(inode);
@@ -312,7 +323,35 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
                 iput(inode);
         }
 
-        /* TODO: use index when looking up by origin inode */
+        /*
+         * For decoded lower dir file handle, lookup index by origin to check
+         * if lower dir was copied up and and/or removed.
+         */
+        if (!this && layer->idx && ofs->indexdir && !WARN_ON(!d_is_dir(real))) {
+                index = ovl_lookup_index(ofs, NULL, real, false);
+                if (IS_ERR(index))
+                        return index;
+        }
+
+        /* Get connected upper overlay dir from index */
+        if (index) {
+                struct dentry *upper = ovl_index_upper(ofs, index);
+
+                dput(index);
+                if (IS_ERR_OR_NULL(upper))
+                        return upper;
+
+                /*
+                 * ovl_lookup_real() in lower layer may call recursively once to
+                 * ovl_lookup_real() in upper layer. The first level call walks
+                 * back lower parents to the topmost indexed parent. The second
+                 * recursive call walks back from indexed upper to the topmost
+                 * connected/hashed upper parent (or up to root).
+                 */
+                this = ovl_lookup_real(sb, upper, &upper_layer);
+                dput(upper);
+        }
+
         if (!this)
                 return NULL;
 
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 6199bf7a77c7..c5449efd96d5 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -661,11 +661,9 @@ struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh)
         return ERR_PTR(err);
 }
 
-static struct dentry *ovl_lookup_index(struct dentry *dentry,
-                                       struct dentry *upper,
-                                       struct dentry *origin)
+struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
+                                struct dentry *origin, bool verify)
 {
-        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
         struct dentry *index;
         struct inode *inode;
         struct qstr name;
@@ -693,6 +691,16 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
         inode = d_inode(index);
         if (d_is_negative(index)) {
                 goto out_dput;
+        } else if (ovl_is_whiteout(index) && !verify) {
+                /*
+                 * When index lookup is called with !verify for decoding an
+                 * overlay file handle, a whiteout index implies that decode
+                 * should treat file handle as stale and no need to print a
+                 * warning about it.
+                 */
+                dput(index);
+                index = ERR_PTR(-ESTALE);
+                goto out;
         } else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
                    ((inode->i_mode ^ d_inode(origin)->i_mode) & S_IFMT)) {
                 /*
@@ -706,7 +714,7 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
                                     index, d_inode(index)->i_mode & S_IFMT,
                                     d_inode(origin)->i_mode & S_IFMT);
                 goto fail;
-        } else if (is_dir) {
+        } else if (is_dir && verify) {
                 if (!upper) {
                         pr_warn_ratelimited("overlayfs: suspected uncovered redirected dir found (origin=%pd2, index=%pd2).\n",
                                             origin, index);
@@ -943,7 +951,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
         if (origin && ovl_indexdir(dentry->d_sb) &&
             (!d.is_dir || ovl_index_all(dentry->d_sb))) {
-                index = ovl_lookup_index(dentry, upperdentry, origin);
+                index = ovl_lookup_index(ofs, upperdentry, origin, true);
                 if (IS_ERR(index)) {
                         err = PTR_ERR(index);
                         index = NULL;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index bf17bf97c50f..0df25a9c94bd 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -274,6 +274,8 @@ struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index);
 int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index);
 int ovl_get_index_name(struct dentry *origin, struct qstr *name);
 struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh);
+struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
+                                struct dentry *origin, bool verify);
 int ovl_path_next(int idx, struct dentry *dentry, struct path *path);
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                           unsigned int flags);