upstream: kbd-interactive device names should be matched against

the full device name, not a prefix. Doesn't matter in practice as there is
only one kbd-int device supported (PAM xor BSD auth), and an attacker would
still need to successfully authenticate against an incorrectly-selected
device.

reported by ashamedbit, NobleMathews; ok deraadt@

OpenBSD-Commit-ID: cf75d4f99405fbb41354c4ae724a3b39a3b58f82

Author: djmdjm

auth2-chall.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-chall.c,v 1.54 2020/10/18 11:32:01 djm Exp $ */
+/* $OpenBSD: auth2-chall.c,v 1.55 2025/09/29 02:32:15 djm Exp $ */
 /*
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2001 Per Allansson.  All rights reserved.
@@ -154,7 +154,7 @@ kbdint_next_device(Authctxt *authctxt, KbdintAuthctxt *kbdintctxt)
 {
 	size_t len;
 	char *t;
-	int i;
+	size_t i;
 
 	if (kbdintctxt->device)
 		kbdint_reset_device(kbdintctxt);
@@ -165,11 +165,14 @@ kbdint_next_device(Authctxt *authctxt, KbdintAuthctxt *kbdintctxt)
 		if (len == 0)
 			break;
 		for (i = 0; devices[i]; i++) {
+			if (i >= sizeof(kbdintctxt->devices_done) * 8)
+				fatal_f("internal error: too may devices");
 			if ((kbdintctxt->devices_done & (1 << i)) != 0 ||
 			    !auth2_method_allowed(authctxt,
 			    "keyboard-interactive", devices[i]->name))
 				continue;
-			if (strncmp(kbdintctxt->devices, devices[i]->name,
+			if (strlen(devices[i]->name) == len &&
+			    memcmp(kbdintctxt->devices, devices[i]->name,
 			    len) == 0) {
 				kbdintctxt->device = devices[i];
 				kbdintctxt->devices_done |= 1 << i;