From b6036e23b0477be147211b4e21a6b49cd4d6c9a0 Mon Sep 17 00:00:00 2001
From: Jamie Bainbridge <jamie.bainbridge@gmail.com>
Date: Wed, 8 Sep 2021 12:08:17 +1000
Subject: [PATCH] gutils: Avoid segfault in g_get_user_database_entry

g_get_user_database_entry() uses variable pwd to store the contents of
the call to getpwnam_r(), then capitalises the first letter of pw_name
with g_ascii_toupper (pw->pw_name[0]).

However, as per the getpwnam manpage, the result of that call "may point
to a static area". When this happens, GLib is trying to edit static
memory which belongs to a shared library, so segfaults.

Instead, copy pw_name off to a temporary variable, set uppercase on
that variable, and use the variable to join into the desired string.
Free the new variable after it is no longer needed.

Signed-off-by: Jamie Bainbridge <jamie.bainbridge@gmail.com>
---
 glib/gutils.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/glib/gutils.c b/glib/gutils.c
index b7a2113d4..4bccd7229 100644
--- a/glib/gutils.c
+++ b/glib/gutils.c
@@ -692,14 +692,17 @@ g_get_user_database_entry (void)
               {
                 gchar **gecos_fields;
                 gchar **name_parts;
+                gchar *uppercase_pw_name;
 
                 /* split the gecos field and substitute '&' */
                 gecos_fields = g_strsplit (pw->pw_gecos, ",", 0);
                 name_parts = g_strsplit (gecos_fields[0], "&", 0);
-                pw->pw_name[0] = g_ascii_toupper (pw->pw_name[0]);
-                e.real_name = g_strjoinv (pw->pw_name, name_parts);
+                uppercase_pw_name = g_strdup (pw->pw_name);
+                uppercase_pw_name[0] = g_ascii_toupper (uppercase_pw_name[0]);
+                e.real_name = g_strjoinv (uppercase_pw_name, name_parts);
                 g_strfreev (gecos_fields);
                 g_strfreev (name_parts);
+                g_free (uppercase_pw_name);
               }
 #endif
 
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