From bb40105fe95b5d95e31715ddb210380d381a1e26 Mon Sep 17 00:00:00 2001
From: Jamie Bainbridge <[email protected]>
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() capitalises the first letter of pw_name
with g_ascii_toupper (pw->pw_name[0]).

However, the manpage for getpwnam() and getpwuid() says the result of
those calls "may point to a static area". GLib is then trying to edit
static memory which belongs to a shared library, so segfaults.

The reentrant variants of the above calls are supposed to fill the user
buffer supplied to them, however Michael Catanzaro also found a bug in
systemd where the data is not copied to the user buffer and still points
to static memory, resulting in the same sort of segfault. See:
https://github.com/systemd/systemd/issues/20679

Solve both these cases in GLib by copying pw_name off to a temporary
variable, set uppercase on that variable, and use the variable to join
into the desired string. Free the variable after it is no longer needed.

Signed-off-by: Jamie Bainbridge <[email protected]>

Conflict:NA
Reference:https://gitlab.gnome.org/GNOME/glib/-/commit/bb40105fe95b5d95e31715ddb210380d381a1e26

---
 glib/gutils.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/glib/gutils.c b/glib/gutils.c
index b7a2113d41..4bccd72297 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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