Fix timing information leak allowing discovery of invalid usernames in PAM

keyboard-interactive authentication (backported from a patch by Darren
Tucker; closes: #281595).

1 files changed, 4 insertions, 7 deletions

diff --git a/auth2-chall.c b/auth2-chall.c
index aacbf0bcc..0f08b05c6 100644
--- a/auth2-chall.c
+++ b/auth2-chall.c
@@ -275,12 +275,9 @@ input_userauth_info_response(int type, u_int32_t seq, void *ctxt)
         }
         packet_check_eom();
 
-        if (authctxt->valid) {
-                res = kbdintctxt->device->respond(kbdintctxt->ctxt,
-                    nresp, response);
-        } else {
-                res = -1;
-        }
+        res = kbdintctxt->device->respond(kbdintctxt->ctxt, nresp, response);
+        if (!authctxt->valid)
+                res = 1;        /* keep going if login invalid */
 
         for (i = 0; i < nresp; i++) {
                 memset(response[i], 'r', strlen(response[i]));
@@ -292,7 +289,7 @@ input_userauth_info_response(int type, u_int32_t seq, void *ctxt)
         switch (res) {
         case 0:
                 /* Success! */
-                authenticated = 1;
+                authenticated = authctxt->valid ? 1 : 0;
                 break;
         case 1:
                 /* Authentication needs further interaction */