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 <[email protected]> Signed-off-by: Paul Mackerras <[email protected]>
ppp-project · Feb 3, 2020 · 8d7970b · 8d7970b
1 parent 858976b
commit 8d7970b
Showing 1 changed file with 2 additions and 2 deletions.
diff --git 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';