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gutils: Avoid segfault in g_get_user_database_entry

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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 <jamie.bainbridge@gmail.com>
This commit is contained in:
Jamie Bainbridge 2021-09-08 12:08:17 +10:00
parent 44666880ad
commit bb40105fe9
1 changed files with 5 additions and 2 deletions
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7
glib/gutils.c
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@ -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