1 files changed, 158 insertions, 0 deletions
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 9f5fb2eb9cf7..bec06490fb13 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -110,3 +110,161 @@ int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
+
+int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
+			      unsigned int max_len,
+			      struct fscrypt_str *disk_link)
+{
+	int err;
+
+	/*
+	 * To calculate the size of the encrypted symlink target we need to know
+	 * the amount of NUL padding, which is determined by the flags set in
+	 * the encryption policy which will be inherited from the directory.
+	 * The easiest way to get access to this is to just load the directory's
+	 * fscrypt_info, since we'll need it to create the dir_entry anyway.
+	 *
+	 * Note: in test_dummy_encryption mode, @dir may be unencrypted.
+	 */
+	err = fscrypt_get_encryption_info(dir);
+	if (err)
+		return err;
+	if (!fscrypt_has_encryption_key(dir))
+		return -ENOKEY;
+
+	/*
+	 * Calculate the size of the encrypted symlink and verify it won't
+	 * exceed max_len.  Note that for historical reasons, encrypted symlink
+	 * targets are prefixed with the ciphertext length, despite this
+	 * actually being redundant with i_size.  This decreases by 2 bytes the
+	 * longest symlink target we can accept.
+	 *
+	 * We could recover 1 byte by not counting a null terminator, but
+	 * counting it (even though it is meaningless for ciphertext) is simpler
+	 * for now since filesystems will assume it is there and subtract it.
+	 */
+	if (!fscrypt_fname_encrypted_size(dir, len,
+					  max_len - sizeof(struct fscrypt_symlink_data),
+					  &disk_link->len))
+		return -ENAMETOOLONG;
+	disk_link->len += sizeof(struct fscrypt_symlink_data);
+
+	disk_link->name = NULL;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink);
+
+int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
+			      unsigned int len, struct fscrypt_str *disk_link)
+{
+	int err;
+	struct qstr iname = QSTR_INIT(target, len);
+	struct fscrypt_symlink_data *sd;
+	unsigned int ciphertext_len;
+
+	err = fscrypt_require_key(inode);
+	if (err)
+		return err;
+
+	if (disk_link->name) {
+		/* filesystem-provided buffer */
+		sd = (struct fscrypt_symlink_data *)disk_link->name;
+	} else {
+		sd = kmalloc(disk_link->len, GFP_NOFS);
+		if (!sd)
+			return -ENOMEM;
+	}
+	ciphertext_len = disk_link->len - sizeof(*sd);
+	sd->len = cpu_to_le16(ciphertext_len);
+
+	err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
+	if (err) {
+		if (!disk_link->name)
+			kfree(sd);
+		return err;
+	}
+	/*
+	 * Null-terminating the ciphertext doesn't make sense, but we still
+	 * count the null terminator in the length, so we might as well
+	 * initialize it just in case the filesystem writes it out.
+	 */
+	sd->encrypted_path[ciphertext_len] = '\0';
+
+	if (!disk_link->name)
+		disk_link->name = (unsigned char *)sd;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
+
+/**
+ * fscrypt_get_symlink - get the target of an encrypted symlink
+ * @inode: the symlink inode
+ * @caddr: the on-disk contents of the symlink
+ * @max_size: size of @caddr buffer
+ * @done: if successful, will be set up to free the returned target
+ *
+ * If the symlink's encryption key is available, we decrypt its target.
+ * Otherwise, we encode its target for presentation.
+ *
+ * This may sleep, so the filesystem must have dropped out of RCU mode already.
+ *
+ * Return: the presentable symlink target or an ERR_PTR()
+ */
+const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
+				unsigned int max_size,
+				struct delayed_call *done)
+{
+	const struct fscrypt_symlink_data *sd;
+	struct fscrypt_str cstr, pstr;
+	int err;
+
+	/* This is for encrypted symlinks only */
+	if (WARN_ON(!IS_ENCRYPTED(inode)))
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * Try to set up the symlink's encryption key, but we can continue
+	 * regardless of whether the key is available or not.
+	 */
+	err = fscrypt_get_encryption_info(inode);
+	if (err)
+		return ERR_PTR(err);
+
+	/*
+	 * For historical reasons, encrypted symlink targets are prefixed with
+	 * the ciphertext length, even though this is redundant with i_size.
+	 */
+
+	if (max_size < sizeof(*sd))
+		return ERR_PTR(-EUCLEAN);
+	sd = caddr;
+	cstr.name = (unsigned char *)sd->encrypted_path;
+	cstr.len = le16_to_cpu(sd->len);
+
+	if (cstr.len == 0)
+		return ERR_PTR(-EUCLEAN);
+
+	if (cstr.len + sizeof(*sd) - 1 > max_size)
+		return ERR_PTR(-EUCLEAN);
+
+	err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
+	if (err)
+		return ERR_PTR(err);
+
+	err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
+	if (err)
+		goto err_kfree;
+
+	err = -EUCLEAN;
+	if (pstr.name[0] == '\0')
+		goto err_kfree;
+
+	pstr.name[pstr.len] = '\0';
+	set_delayed_call(done, kfree_link, pstr.name);
+	return pstr.name;
+
+err_kfree:
+	kfree(pstr.name);
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL_GPL(fscrypt_get_symlink);