NetBSD Problem Report #59540

From www@netbsd.org  Mon Jul 21 18:58:50 2025
Return-Path: <www@netbsd.org>
Received: from mail.netbsd.org (mail.netbsd.org [199.233.217.200])
	(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
	 key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256
	 client-signature RSA-PSS (2048 bits) client-digest SHA256)
	(Client CN "mail.NetBSD.org", Issuer "mail.NetBSD.org CA" (not verified))
	by mollari.NetBSD.org (Postfix) with ESMTPS id 96CF91A9239
	for <gnats-bugs@gnats.NetBSD.org>; Mon, 21 Jul 2025 18:58:50 +0000 (UTC)
Message-Id: <20250721185849.3511D1A923C@mollari.NetBSD.org>
Date: Mon, 21 Jul 2025 18:58:49 +0000 (UTC)
From: rwhitlock22@gmail.com
Reply-To: rwhitlock22@gmail.com
To: gnats-bugs@NetBSD.org
Subject: strlcpy(3) has an off-by-one in the manual page
X-Send-Pr-Version: www-1.0

>Number:         59540
>Category:       lib
>Synopsis:       strlcpy(3) has an off-by-one in the manual page
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          doc-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 21 19:00:00 +0000 2025
>Originator:     Robert Whitlock
>Release:        NetBSD current, 10.99.14, July 11, 2025
>Organization:
>Environment:
see above
>Description:
strlcpy(3) claims that strlcpy leaves bytes past dst[strlen(src) + 1] uninitialized, when it would be more precise to say that it leaves bytes past dst[strlen(src)] uninitialized. This can be easily seen by considering the case where src is the empty string "". Then strlen(src) == 0 and dst[strlen(src) + 1] == dst[1], which is one past the terminating NUL byte that is there when strlcpy has finished. The first byte past dst[1] is then the second byte past the NUL terminating byte.

The patch also includes a minor formatting fix.
>How-To-Repeat:
man strlcpy
>Fix:
Index: strlcpy.3
===================================================================
RCS file: /cvsroot/src/lib/libc/string/strlcpy.3,v
retrieving revision 1.25
diff -u -r1.25 strlcpy.3
--- strlcpy.3	2 Apr 2025 00:50:19 -0000	1.25
+++ strlcpy.3	21 Jul 2025 18:18:15 -0000
@@ -79,7 +79,7 @@
 then the
 .Fn strlcat
 function returns
-.Fa size + Fn strlen src
+.Fa size Li + Fn strlen src
 without writing anything to
 .Fa dst .
 .Pp
@@ -146,11 +146,11 @@
 \(em
 .Fn strlcpy
 leaves bytes past
-.Fa dst Ns Li "[" Fn strlen src Li "+ 1" Ns Li "]"
+.Fa dst Ns Li "[" Fn strlen src Ns Li "]"
 uninitialized, and
 .Fn strlcat
 leaves bytes past
-.Fa dst Ns Li "[" Fn strlen dst Li + Fn strlen src Li + 1 Ns Li "]"
+.Fa dst Ns Li "[" Fn strlen dst Li + Fn strlen src Ns Li "]"
 uninitialized.
 This can lead to security vulnerabilities such as leaking secrets from
 uninitialized stack or heap buffers.

Home	PR Database Search