glib-aux: fix nm_str_buf_finalize() for cloning buffer

NMStrBuf can also contains NUL characters. We thus cannot use g_strndup(),
which uses strncpy() and truncates at the first NUL.

Fixes: 13d25f9d0b2f ('glib-aux: add support for starting with stack-allocated buffer in NMStrBuf')
(cherry picked from commit 520411623d874803c18c4f29d13eeea7d5d5a6ac)
(cherry picked from commit 7a3de841b8395df0e9d582be7fa00fcbbc8e998d)

2 files changed, 14 insertions, 1 deletions

diff --git a/src/libnm-glib-aux/nm-str-buf.h b/src/libnm-glib-aux/nm-str-buf.h
index 8d68c1eee3..e8b51208a9 100644
--- a/src/libnm-glib-aux/nm-str-buf.h
+++ b/src/libnm-glib-aux/nm-str-buf.h
@@ -530,7 +530,10 @@ nm_str_buf_finalize(NMStrBuf *strbuf, gsize *out_len)
         char *str = g_steal_pointer(&strbuf->_priv_str);
         char *result;
 
-        result = g_strndup(str, strbuf->_priv_len);
+        result = g_new(char, strbuf->_priv_len + 1u);
+        memcpy(result, str, strbuf->_priv_len);
+        result[strbuf->_priv_len] = '\0';
+
         if (strbuf->_priv_do_bzero_mem)
             nm_explicit_bzero(str, strbuf->_priv_len);
         return result;
diff --git a/src/libnm-glib-aux/tests/test-shared-general.c b/src/libnm-glib-aux/tests/test-shared-general.c
index 225049f1bb..8fb9b7e022 100644
--- a/src/libnm-glib-aux/tests/test-shared-general.c
+++ b/src/libnm-glib-aux/tests/test-shared-general.c
@@ -969,6 +969,16 @@ test_nm_str_buf(void)
         } else
             g_assert(stack_buf != nm_str_buf_get_str(&strbuf));
     }
+
+    {
+        nm_auto_str_buf NMStrBuf s1  = NM_STR_BUF_INIT_A(10, nmtst_get_rand_bool());
+        gs_free char            *str = NULL;
+        gsize                    l;
+
+        nm_str_buf_append_len(&s1, "a\0b", 3);
+        str = nm_str_buf_finalize(&s1, &l);
+        g_assert_cmpmem(str, l + 1, "a\0b", 4);
+    }
 }
 
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