From a926a26f0c69ab10e3f9a5335b84b4ab4ac91db1 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 11 Mar 2023 13:43:36 -0800
Subject: [PATCH] Fix change_field() buffer underrun

* lib/fields.c (change_field): Don't point
before array start; that has undefined behavior.

Signed-off-by: Paul Eggert <eggert@cs.ucla.edu>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
---
 lib/fields.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lib/fields.c b/lib/fields.c
index fa5fd156..640be931 100644
--- a/lib/fields.c
+++ b/lib/fields.c
@@ -91,8 +91,9 @@ void change_field (char *buf, size_t maxsize, const char *prompt)
 		 * entering a space.  --marekm
 		 */
 
-		while (--cp >= newf && isspace (*cp));
-		cp++;
+		while (newf < cp && isspace (cp[-1])) {
+			cp--;
+		}
 		*cp = '\0';
 
 		cp = newf;