From 8d7970b8f3db727fe798b65f3377fe6787575426 Mon Sep 17 00:00:00 2001
From: Paul Mackerras <paulus@ozlabs.org>
Date: Mon, 3 Feb 2020 15:53:28 +1100
Subject: [PATCH] pppd: Fix bounds check in EAP code

Given that we have just checked vallen < len, it can never be the case
that vallen >= len + sizeof(rhostname).  This fixes the check so we
actually avoid overflowing the rhostname array.

Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
---
 pppd/eap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pppd/eap.c b/pppd/eap.c
index 94407f56..1b93db01 100644
--- a/pppd/eap.c
+++ b/pppd/eap.c
@@ -1420,7 +1420,7 @@ int len;
 		}
 
 		/* Not so likely to happen. */
-		if (vallen >= len + sizeof (rhostname)) {
+		if (len - vallen >= sizeof (rhostname)) {
 			dbglog("EAP: trimming really long peer name down");
 			BCOPY(inp + vallen, rhostname, sizeof (rhostname) - 1);
 			rhostname[sizeof (rhostname) - 1] = '\0';
@@ -1846,7 +1846,7 @@ int len;
 		}
 
 		/* Not so likely to happen. */
-		if (vallen >= len + sizeof (rhostname)) {
+		if (len - vallen >= sizeof (rhostname)) {
 			dbglog("EAP: trimming really long peer name down");
 			BCOPY(inp + vallen, rhostname, sizeof (rhostname) - 1);
 			rhostname[sizeof (rhostname) - 1] = '\0';