From c480428e3767cac53dcafa29b03ce31e0da1efc9 Mon Sep 17 00:00:00 2001
From: =?utf8?q?P=C3=A1draig=20Brady?= <P@draigBrady.com>
Date: Thu, 7 Aug 2025 20:39:24 +0100
Subject: [PATCH] basenc: fix stripping of '=' chars in some encodings

* src/basenc.c (do_decode): With -i ensure we strip '=' chars
if there is no padding for the chosen encoding.
* tests/basenc/basenc.pl: Add a test case.
* NEWS: Mention the bug fix.
---
 NEWS                   | 4 ++++
 src/basenc.c           | 3 ++-
 tests/basenc/basenc.pl | 1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index 473c7a798d..f97c7e4a19 100644
--- a/NEWS
+++ b/NEWS
@@ -12,6 +12,10 @@ GNU coreutils NEWS                                    -*- outline -*-
 
 ** Bug fixes
 
+  'basenc -d -i' will now strip '=' characters from the input
+  in encodings where padding characters are not valid.
+  [bug introduced with the basenc program in coreutils-8.31]
+
   cksum was not compilable by Apple LLVM 10.0.0 x86-64, which
   lacks support for checking for the VPCLMULQDQ instruction.
   [bug introduced in coreutils-9.6]
diff --git a/src/basenc.c b/src/basenc.c
index c445e6f41a..4993c00253 100644
--- a/src/basenc.c
+++ b/src/basenc.c
@@ -1159,7 +1159,8 @@ do_decode (FILE *in, char const *infile, FILE *out, bool ignore_garbage)
             {
               for (idx_t i = 0; n > 0 && i < n;)
                 {
-                  if (isubase (inbuf[sum + i]) || inbuf[sum + i] == '=')
+                  if (isubase (inbuf[sum + i])
+                      || (REQUIRED_PADDING (1) && inbuf[sum + i] == '='))
                     i++;
                   else
                     memmove (inbuf + sum + i, inbuf + sum + i + 1, --n - i);
diff --git a/tests/basenc/basenc.pl b/tests/basenc/basenc.pl
index c598d29e5b..94f6c2b326 100755
--- a/tests/basenc/basenc.pl
+++ b/tests/basenc/basenc.pl
@@ -168,6 +168,7 @@ my @Tests =
  ['b2m_2', '--base2m -d',     {IN=>'11000001'},   {OUT=>"\xC1"}],
  ['b2m_3', '--base2m -d',     {IN=>"110\n00001"}, {OUT=>"\xC1"}],
  ['b2m_4', '--base2m -di',    {IN=>"110x00001"},  {OUT=>"\xC1"}],
+ ['b2m_4p', '--base2m -di',   {IN=>"=11000001="}, {OUT=>"\xC1"}],
  ['b2m_5', '--base2m -d',     {IN=>"110x00001"},  {EXIT=>1},
   {ERR=>"$prog: invalid input\n"}],
  ['b2m_6', '--base2m -d',     {IN=>"11000001x"},  {OUT=>"\xC1"}, {EXIT=>1},
-- 
2.47.3