Use bcrypt to hash passwords

Replace the default hash function used for storing passwords by
password_hash() which internally uses bcrypt. Legacy MD5 hashes are
still supported and are immediately converted to the new format when a
user logs in.

Since big parts of the authentication system needed to be rewritten in
this context, this patch also includes some simplification and
refactoring of all code related to password checking and resetting.

Fixes FS#52297.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

3 files changed, 61 insertions, 145 deletions

diff --git a/web/html/passreset.php b/web/html/passreset.php
index cb2f6bcd..e89967d4 100644
--- a/web/html/passreset.php
+++ b/web/html/passreset.php
@@ -34,10 +34,7 @@ if (isset($_GET['resetkey'], $_POST['email'], $_POST['password'], $_POST['confir
 	}
 
 	if (empty($error)) {
-		$salt = generate_salt();
-		$hash = salted_hash($password, $salt);
-
-		$error = password_reset($hash, $salt, $resetkey, $email);
+		$error = password_reset($password, $resetkey, $email);
 	}
 } elseif (isset($_POST['email'])) {
 	$email = $_POST['email'];
diff --git a/web/lib/acctfuncs.inc.php b/web/lib/acctfuncs.inc.php
index b3cf6122..d0a7ff94 100644
--- a/web/lib/acctfuncs.inc.php
+++ b/web/lib/acctfuncs.inc.php
@@ -272,13 +272,12 @@ function process_account_form($TYPE,$A,$U="",$T="",$S="",$E="",$H="",$P="",$C=""
 
 	if ($TYPE == "new") {
 		/* Create an unprivileged user. */
-		$salt = generate_salt();
 		if (empty($P)) {
 			$send_resetkey = true;
 			$email = $E;
 		} else {
 			$send_resetkey = false;
-			$P = salted_hash($P, $salt);
+			$P = password_hash($P, PASSWORD_DEFAULT);
 		}
 		$U = $dbh->quote($U);
 		$E = $dbh->quote($E);
@@ -291,9 +290,9 @@ function process_account_form($TYPE,$A,$U="",$T="",$S="",$E="",$H="",$P="",$C=""
 		$I = $dbh->quote($I);
 		$K = $dbh->quote(str_replace(" ", "", $K));
 		$q = "INSERT INTO Users (AccountTypeID, Suspended, ";
-		$q.= "InactivityTS, Username, Email, Passwd, Salt, ";
+		$q.= "InactivityTS, Username, Email, Passwd , ";
 		$q.= "RealName, LangPreference, Timezone, Homepage, IRCNick, PGPKey) ";
-		$q.= "VALUES (1, 0, 0, $U, $E, $P, $salt, $R, $L, $TZ ";
+		$q.= "VALUES (1, 0, 0, $U, $E, $P, $R, $L, $TZ ";
 		$q.= "$HP, $I, $K)";
 		$result = $dbh->exec($q);
 		if (!$result) {
@@ -350,9 +349,8 @@ function process_account_form($TYPE,$A,$U="",$T="",$S="",$E="",$H="",$P="",$C=""
 			$q.= ", HideEmail = 0";
 		}
 		if ($P) {
-			$salt = generate_salt();
-			$hash = salted_hash($P, $salt);
-			$q .= ", Passwd = '$hash', Salt = '$salt'";
+			$hash = password_hash($P, PASSWORD_DEFAULT);
+			$q .= ", Passwd = " . $dbh->quote($hash);
 		}
 		$q.= ", RealName = " . $dbh->quote($R);
 		$q.= ", LangPreference = " . $dbh->quote($L);
@@ -528,19 +526,24 @@ function try_login() {
 	if (user_suspended($userID)) {
 		$login_error = __('Account suspended');
 		return array('SID' => '', 'error' => $login_error);
-	} elseif (passwd_is_empty($userID)) {
-		$login_error = __('Your password has been reset. ' .
-			'If you just created a new account, please ' .
-			'use the link from the confirmation email ' .
-			'to set an initial password. Otherwise, ' .
-			'please request a reset key on the %s' .
-			'Password Reset%s page.', '<a href="' .
-			htmlspecialchars(get_uri('/passreset')) . '">',
-			'</a>');
-		return array('SID' => '', 'error' => $login_error);
-	} elseif (!valid_passwd($userID, $_REQUEST['passwd'])) {
-		$login_error = __("Bad username or password.");
-		return array('SID' => '', 'error' => $login_error);
+	}
+
+	switch (check_passwd($userID, $_REQUEST['passwd'])) {
+		case -1:
+			$login_error = __('Your password has been reset. ' .
+				'If you just created a new account, please ' .
+				'use the link from the confirmation email ' .
+				'to set an initial password. Otherwise, ' .
+				'please request a reset key on the %s' .
+				'Password Reset%s page.', '<a href="' .
+				htmlspecialchars(get_uri('/passreset')) . '">',
+				'</a>');
+			return array('SID' => '', 'error' => $login_error);
+		case 0:
+			$login_error = __("Bad username or password.");
+			return array('SID' => '', 'error' => $login_error);
+		case 1:
+			break;
 	}
 
 	$logged_in = 0;
@@ -736,18 +739,18 @@ function send_resetkey($email, $welcome=false) {
 /**
  * Change a user's password in the database if reset key and e-mail are correct
  *
- * @param string $hash New MD5 hash of a user's password
- * @param string $salt New salt for the user's password
+ * @param string $password The new password
  * @param string $resetkey Code e-mailed to a user to reset a password
  * @param string $email E-mail address of the user resetting their password
  *
  * @return string|void Redirect page if successful, otherwise return error message
  */
-function password_reset($hash, $salt, $resetkey, $email) {
+function password_reset($password, $resetkey, $email) {
+	$hash = password_hash($password, PASSWORD_DEFAULT);
+
 	$dbh = DB::connect();
-	$q = "UPDATE Users ";
-	$q.= "SET Passwd = '$hash', ";
-	$q.= "Salt = '$salt', ";
+	$q = "UPDATE Users SET ";
+	$q.= "Passwd = " . $dbh->quote($hash) . ", ";
 	$q.= "ResetKey = '' ";
 	$q.= "WHERE ResetKey != '' ";
 	$q.= "AND ResetKey = " . $dbh->quote($resetkey) . " ";
@@ -778,75 +781,48 @@ function good_passwd($passwd) {
 /**
  * Determine if the password is correct and salt it if it hasn't been already
  *
- * @param string $userID The user ID to check the password against
+ * @param int $user_id The user ID to check the password against
  * @param string $passwd The password the visitor sent
  *
- * @return bool True if password was correct and properly salted, otherwise false
+ * @return int Positive if password is correct, negative if password is unset
  */
-function valid_passwd($userID, $passwd) {
+function check_passwd($user_id, $passwd) {
 	$dbh = DB::connect();
-	if ($passwd == "") {
-		return false;
-	}
 
-	/* Get salt for this user. */
-	$salt = get_salt($userID);
-	if ($salt) {
-		$q = "SELECT ID FROM Users ";
-		$q.= "WHERE ID = " . $userID . " ";
-		$q.= "AND Passwd = " . $dbh->quote(salted_hash($passwd, $salt));
-		$result = $dbh->query($q);
-		if (!$result) {
-			return false;
-		}
-
-		$row = $result->fetch(PDO::FETCH_NUM);
-		return ($row[0] > 0);
-	} else {
-		/* Check password without using salt. */
-		$q = "SELECT ID FROM Users ";
-		$q.= "WHERE ID = " . $userID . " ";
-		$q.= "AND Passwd = " . $dbh->quote(md5($passwd));
-		$result = $dbh->query($q);
-		if (!$result) {
-			return false;
-		}
-
-		$row = $result->fetch(PDO::FETCH_NUM);
-		if (!$row[0]) {
-			return false;
-		}
+	/* Get password hash and salt. */
+	$q = "SELECT Passwd, Salt FROM Users WHERE ID = " . intval($user_id);
+	$result = $dbh->query($q);
+	if (!$result) {
+		return 0;
+	}
+	$row = $result->fetch(PDO::FETCH_ASSOC);
+	if (!$row) {
+		return 0;
+	}
+	$hash = $row['Passwd'];
+	$salt = $row['Salt'];
+	if (!$hash) {
+		return -1;
+	}
 
-		/* Password correct, but salt it first! */
-		if (!save_salt($userID, $passwd)) {
-			trigger_error("Unable to salt user's password;" .
-				" ID " . $userID, E_USER_WARNING);
-			return false;
+	/* Verify the password hash. */
+	if (!password_verify($passwd, $hash)) {
+		/* Invalid password, fall back to MD5. */
+		if (md5($salt . $passwd) != $hash) {
+			return 0;
 		}
-
-		return true;
 	}
-}
 
-/**
- * Determine if a user's password is empty
- *
- * @param string $uid The user ID to check for an empty password
- *
- * @return bool True if the user's password is empty, otherwise false
- */
-function passwd_is_empty($uid) {
-	$dbh = DB::connect();
-
-	$q = "SELECT * FROM Users WHERE ID = " . $dbh->quote($uid) . " ";
-	$q .= "AND Passwd = " . $dbh->quote('');
-	$result = $dbh->query($q);
+	/* Password correct, migrate the hash if necessary. */
+	if (password_needs_rehash($hash, PASSWORD_DEFAULT)) {
+		$hash = password_hash($passwd, PASSWORD_DEFAULT);
 
-	if ($result->fetchColumn()) {
-		return true;
-	} else {
-		return false;
+		$q = "UPDATE Users SET Passwd = " . $dbh->quote($hash) . " ";
+		$q.= "WHERE ID = " . intval($user_id);
+		$dbh->query($q);
 	}
+
+	return 1;
 }
 
 /**
diff --git a/web/lib/aur.inc.php b/web/lib/aur.inc.php
index 94a38499..d58df406 100644
--- a/web/lib/aur.inc.php
+++ b/web/lib/aur.inc.php
@@ -538,63 +538,6 @@ function mkurl($append) {
 }
 
 /**
- * Determine a user's salt from the database
- *
- * @param string $user_id The user ID of the user trying to log in
- *
- * @return string|void Return the salt for the requested user, otherwise void
- */
-function get_salt($user_id) {
-	$dbh = DB::connect();
-	$q = "SELECT Salt FROM Users WHERE ID = " . $user_id;
-	$result = $dbh->query($q);
-	if ($result) {
-		$row = $result->fetch(PDO::FETCH_NUM);
-		return $row[0];
-	}
-	return;
-}
-
-/**
- * Save a user's salted password in the database
- *
- * @param string $user_id The user ID of the user who is salting their password
- * @param string $passwd The password of the user logging in
- */
-function save_salt($user_id, $passwd) {
-	$dbh = DB::connect();
-	$salt = generate_salt();
-	$hash = salted_hash($passwd, $salt);
-	$q = "UPDATE Users SET Salt = " . $dbh->quote($salt) . ", ";
-	$q.= "Passwd = " . $dbh->quote($hash) . " WHERE ID = " . $user_id;
-	return $dbh->exec($q);
-}
-
-/**
- * Generate a string to be used for salting passwords
- *
- * @return string MD5 hash of concatenated random number and current time
- */
-function generate_salt() {
-	return md5(uniqid(mt_rand(), true));
-}
-
-/**
- * Combine salt and password to form a hash
- *
- * @param string $passwd User plaintext password
- * @param string $salt MD5 hash to be used as user salt
- *
- * @return string The MD5 hash of the concatenated salt and user password
- */
-function salted_hash($passwd, $salt) {
-	if (strlen($salt) != 32) {
-		trigger_error('Salt does not look like an md5 hash', E_USER_WARNING);
-	}
-	return md5($salt . $passwd);
-}
-
-/**
  * Get a package comment
  *
  * @param  int $comment_id The ID of the comment