ovl: lookup index entry for copy up origin

When inodes index feature is enabled, lookup in indexdir for the index
entry of lower real inode or copy up origin inode. The index entry name
is the hex representation of the lower inode file handle.

If the index dentry in negative, then either no lower aliases have been
copied up yet, or aliases have been copied up in older kernels and are
not indexed.

If the index dentry for a copy up origin inode is positive, but points
to an inode different than the upper inode, then either the upper inode
has been copied up and not indexed or it was indexed, but since then
index dir was cleared. Either way, that index cannot be used to indentify
the overlay inode.

If a positive dentry that matches the upper inode was found, then it is
safe to use the copy up origin st_ino for upper hardlinks, because all
indexed upper hardlinks are represented by the same overlay inode as the
copy up origin.

Set the INDEX type flag on an indexed upper dentry. A non-upper dentry
may also have a positive index from copy up of another lower hardlink.
This situation will be handled by following patches.

Index lookup is going to be used to prevent breaking hardlinks on copy up.

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

1 files changed, 108 insertions, 0 deletions

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 0c816e9aa50c..3bec4cb39967 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -379,6 +379,94 @@ fail:
 }
 
 /*
+ * Lookup in indexdir for the index entry of a lower real inode or a copy up
+ * origin inode. The index entry name is the hex representation of the lower
+ * inode file handle.
+ *
+ * If the index dentry in negative, then either no lower aliases have been
+ * copied up yet, or aliases have been copied up in older kernels and are
+ * not indexed.
+ *
+ * If the index dentry for a copy up origin inode is positive, but points
+ * to an inode different than the upper inode, then either the upper inode
+ * has been copied up and not indexed or it was indexed, but since then
+ * index dir was cleared. Either way, that index cannot be used to indentify
+ * the overlay inode.
+ */
+int ovl_get_index_name(struct dentry *origin, struct qstr *name)
+{
+	int err;
+	struct ovl_fh *fh;
+	char *n, *s;
+
+	fh = ovl_encode_fh(origin, false);
+	if (IS_ERR(fh))
+		return PTR_ERR(fh);
+
+	err = -ENOMEM;
+	n = kzalloc(fh->len * 2, GFP_TEMPORARY);
+	if (n) {
+		s  = bin2hex(n, fh, fh->len);
+		*name = (struct qstr) QSTR_INIT(n, s - n);
+		err = 0;
+	}
+	kfree(fh);
+
+	return err;
+
+}
+
+static struct dentry *ovl_lookup_index(struct dentry *dentry,
+				       struct dentry *upper,
+				       struct dentry *origin)
+{
+	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+	struct dentry *index;
+	struct inode *inode;
+	struct qstr name;
+	int err;
+
+	err = ovl_get_index_name(origin, &name);
+	if (err)
+		return ERR_PTR(err);
+
+	index = lookup_one_len_unlocked(name.name, ofs->indexdir, name.len);
+	if (IS_ERR(index)) {
+		pr_warn_ratelimited("overlayfs: failed inode index lookup (ino=%lu, key=%*s, err=%i);\n"
+				    "overlayfs: mount with '-o index=off' to disable inodes index.\n",
+				    d_inode(origin)->i_ino, name.len, name.name,
+				    err);
+		goto out;
+	}
+
+	if (d_is_negative(index)) {
+		if (upper && d_inode(origin)->i_nlink > 1) {
+			pr_warn_ratelimited("overlayfs: hard link with origin but no index (ino=%lu).\n",
+					    d_inode(origin)->i_ino);
+			goto fail;
+		}
+
+		dput(index);
+		index = NULL;
+	} else if (upper && d_inode(index) != d_inode(upper)) {
+		inode = d_inode(index);
+		pr_warn_ratelimited("overlayfs: wrong index found (index ino: %lu, upper ino: %lu).\n",
+				    d_inode(index)->i_ino,
+				    d_inode(upper)->i_ino);
+		goto fail;
+	}
+
+out:
+	kfree(name.name);
+	return index;
+
+fail:
+	dput(index);
+	index = ERR_PTR(-EIO);
+	goto out;
+}
+
+/*
  * Returns next layer in stack starting from top.
  * Returns -1 if this is the last layer.
  */
@@ -409,6 +497,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
 	struct path *stack = NULL;
 	struct dentry *upperdir, *upperdentry = NULL;
+	struct dentry *index = NULL;
 	unsigned int ctr = 0;
 	struct inode *inode = NULL;
 	bool upperopaque = false;
@@ -506,6 +595,18 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		}
 	}
 
+	/* Lookup index by lower inode and verify it matches upper inode */
+	if (ctr && !d.is_dir && ovl_indexdir(dentry->d_sb)) {
+		struct dentry *origin = stack[0].dentry;
+
+		index = ovl_lookup_index(dentry, upperdentry, origin);
+		if (IS_ERR(index)) {
+			err = PTR_ERR(index);
+			index = NULL;
+			goto out_put;
+		}
+	}
+
 	oe = ovl_alloc_entry(ctr);
 	err = -ENOMEM;
 	if (!oe)
@@ -515,6 +616,9 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
 	dentry->d_fsdata = oe;
 
+	if (index && !upperdentry)
+		upperdentry = dget(index);
+
 	if (upperdentry || ctr) {
 		err = -ENOMEM;
 		inode = ovl_get_inode(dentry, upperdentry);
@@ -522,9 +626,12 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			goto out_free_oe;
 
 		OVL_I(inode)->redirect = upperredirect;
+		if (index)
+			ovl_set_flag(OVL_INDEX, inode);
 	}
 
 	revert_creds(old_cred);
+	dput(index);
 	kfree(stack);
 	kfree(d.redirect);
 	d_add(dentry, inode);
@@ -535,6 +642,7 @@ out_free_oe:
 	dentry->d_fsdata = NULL;
 	kfree(oe);
 out_put:
+	dput(index);
 	for (i = 0; i < ctr; i++)
 		dput(stack[i].dentry);
 	kfree(stack);