ovl: Handle verity during copy-up

During regular metacopy, if lowerdata file has fs-verity enabled, and
the verity option is enabled, we add the digest to the metacopy xattr.

If verity is required, and lowerdata does not have fs-verity enabled,
fall back to full copy-up (or the generated metacopy would not
validate).

Signed-off-by: Alexander Larsson <alexl@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

Author: alexlarsson

fs/overlayfs/copy_up.c

@@ -544,6 +544,7 @@ struct ovl_copy_up_ctx {
 	bool origin;
 	bool indexed;
 	bool metacopy;
+	bool metacopy_digest;
 };
 
 static int ovl_link_up(struct ovl_copy_up_ctx *c)
@@ -641,8 +642,20 @@ static int ovl_copy_up_metadata(struct ovl_copy_up_ctx *c, struct dentry *temp)
 	}
 
 	if (c->metacopy) {
-		err = ovl_check_setxattr(ofs, temp, OVL_XATTR_METACOPY,
-					 NULL, 0, -EOPNOTSUPP);
+		struct path lowerdatapath;
+		struct ovl_metacopy metacopy_data = OVL_METACOPY_INIT;
+
+		ovl_path_lowerdata(c->dentry, &lowerdatapath);
+		if (WARN_ON_ONCE(lowerdatapath.dentry == NULL))
+			return -EIO;
+		err = ovl_get_verity_digest(ofs, &lowerdatapath, &metacopy_data);
+		if (err)
+			return err;
+
+		if (metacopy_data.digest_algo)
+			c->metacopy_digest = true;
+
+		err = ovl_set_metacopy_xattr(ofs, temp, &metacopy_data);
 		if (err)
 			return err;
 	}
@@ -751,9 +764,15 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
 	if (err)
 		goto cleanup;
 
-	if (!c->metacopy)
-		ovl_set_upperdata(d_inode(c->dentry));
 	inode = d_inode(c->dentry);
+	if (c->metacopy_digest)
+		ovl_set_flag(OVL_HAS_DIGEST, inode);
+	else
+		ovl_clear_flag(OVL_HAS_DIGEST, inode);
+	ovl_clear_flag(OVL_VERIFIED_DIGEST, inode);
+
+	if (!c->metacopy)
+		ovl_set_upperdata(inode);
 	ovl_inode_update(inode, temp);
 	if (S_ISDIR(inode->i_mode))
 		ovl_set_flag(OVL_WHITEOUTS, inode);
@@ -813,6 +832,12 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
 	if (err)
 		goto out_fput;
 
+	if (c->metacopy_digest)
+		ovl_set_flag(OVL_HAS_DIGEST, d_inode(c->dentry));
+	else
+		ovl_clear_flag(OVL_HAS_DIGEST, d_inode(c->dentry));
+	ovl_clear_flag(OVL_VERIFIED_DIGEST, d_inode(c->dentry));
+
 	if (!c->metacopy)
 		ovl_set_upperdata(d_inode(c->dentry));
 	ovl_inode_update(d_inode(c->dentry), dget(temp));
@@ -918,6 +943,19 @@ static bool ovl_need_meta_copy_up(struct dentry *dentry, umode_t mode,
 	if (flags && ((OPEN_FMODE(flags) & FMODE_WRITE) || (flags & O_TRUNC)))
 		return false;
 
+	/* Fall back to full copy if no fsverity on source data and we require verity */
+	if (ofs->config.verity_mode == OVL_VERITY_REQUIRE) {
+		struct path lowerdata;
+
+		ovl_path_lowerdata(dentry, &lowerdata);
+
+		if (WARN_ON_ONCE(lowerdata.dentry == NULL) ||
+		    ovl_ensure_verity_loaded(&lowerdata) ||
+		    !fsverity_active(d_inode(lowerdata.dentry))) {
+			return false;
+		}
+	}
+
 	return true;
 }
 
@@ -984,6 +1022,8 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
 	if (err)
 		goto out_free;
 
+	ovl_clear_flag(OVL_HAS_DIGEST, d_inode(c->dentry));
+	ovl_clear_flag(OVL_VERIFIED_DIGEST, d_inode(c->dentry));
 	ovl_set_upperdata(d_inode(c->dentry));
 out_free:
 	kfree(capability);

fs/overlayfs/overlayfs.h

@@ -487,11 +487,14 @@ int ovl_set_metacopy_xattr(struct ovl_fs *ofs, struct dentry *d,
 			   struct ovl_metacopy *metacopy);
 bool ovl_is_metacopy_dentry(struct dentry *dentry);
 char *ovl_get_redirect_xattr(struct ovl_fs *ofs, const struct path *path, int padding);
+int ovl_ensure_verity_loaded(struct path *path);
 int ovl_get_verity_xattr(struct ovl_fs *ofs, const struct path *path,
 			 u8 *digest_buf, int *buf_length);
 int ovl_validate_verity(struct ovl_fs *ofs,
 			struct path *metapath,
 			struct path *datapath);
+int ovl_get_verity_digest(struct ovl_fs *ofs, struct path *src,
+			  struct ovl_metacopy *metacopy);
 int ovl_sync_status(struct ovl_fs *ofs);
 
 static inline void ovl_set_flag(unsigned long flag, struct inode *inode)

fs/overlayfs/util.c

@@ -1188,7 +1188,7 @@ char *ovl_get_redirect_xattr(struct ovl_fs *ofs, const struct path *path, int pa
 }
 
 /* Call with mounter creds as it may open the file */
-static int ovl_ensure_verity_loaded(struct path *datapath)
+int ovl_ensure_verity_loaded(struct path *datapath)
 {
 	struct inode *inode = d_inode(datapath->dentry);
 	struct file *filp;
@@ -1262,6 +1262,37 @@ int ovl_validate_verity(struct ovl_fs *ofs,
 	return 0;
 }
 
+int ovl_get_verity_digest(struct ovl_fs *ofs, struct path *src,
+			  struct ovl_metacopy *metacopy)
+{
+	int err, digest_size;
+
+	if (!ofs->config.verity_mode || !S_ISREG(d_inode(src->dentry)->i_mode))
+		return 0;
+
+	err = ovl_ensure_verity_loaded(src);
+	if (err < 0) {
+		pr_warn_ratelimited("lower file '%pd' failed to load fs-verity info\n",
+				    src->dentry);
+		return -EIO;
+	}
+
+	digest_size = fsverity_get_digest(d_inode(src->dentry),
+					  metacopy->digest, &metacopy->digest_algo, NULL);
+	if (digest_size == 0 ||
+	    WARN_ON_ONCE(digest_size > FS_VERITY_MAX_DIGEST_SIZE)) {
+		if (ofs->config.verity_mode == OVL_VERITY_REQUIRE) {
+			pr_warn_ratelimited("lower file '%pd' has no fs-verity digest\n",
+					    src->dentry);
+			return -EIO;
+		}
+		return 0;
+	}
+
+	metacopy->len += digest_size;
+	return 0;
+}
+
 /*
  * ovl_sync_status() - Check fs sync status for volatile mounts
  *