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user-accounts: Fix definition of MAXNAMELEN

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Currently we get MAXNAMELEN from glibc's LOGIN_NAME_MAX, if available,
and sysconf otherwise. But the maximum username length supported by
glibc and the kernel is actually way larger than the maximum length that
actually works in practice. On Linux, anything larger than 32 characters
is not going to fit into utmp, and will therefore be rejected by
useradd. Then gnome-control-center will spit out a confusing error
message dialog.

Let's spare our users from that.

useradd (in shadow-utils) gets its max name size from the following
magic:

 /* Maximum length of usernames */
 #ifdef HAVE_UTMPX_H
 # include <utmpx.h>
 # define USER_NAME_MAX_LENGTH (sizeof (((struct utmpx *)NULL)->ut_user))
 #else
 # include <utmp.h>
 # ifdef HAVE_STRUCT_UTMP_UT_USER
 #  define USER_NAME_MAX_LENGTH (sizeof (((struct utmp *)NULL)->ut_user))
 # else
 #  ifdef HAVE_STRUCT_UTMP_UT_NAME
 #   define USER_NAME_MAX_LENGTH (sizeof (((struct utmp *)NULL)->ut_name))
 #  else
 #   define USER_NAME_MAX_LENGTH 32
 #  endif
 # endif
 #endif

It's more work than necessary. utmpx is standardized by POSIX (it's
actually an XSI extension), whereas utmp is not, so let's just use
utmpx. This ought to work on at least FreeBSD as well. And if any free
operating systems that care about GNOME don't have utmpx yet, no doubt
they'll send patches.

https://bugzilla.gnome.org/show_bug.cgi?id=724193
This commit is contained in:
Michael Catanzaro 2018-01-31 14:31:02 -06:00
parent d14e1b830a
commit 09b94a9b53
1 changed files with 7 additions and 18 deletions
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25
panels/user-accounts/um-utils.c
View file

@ -25,6 +25,7 @@
#include <sys/types.h>
#include <limits.h>
#include <unistd.h>
#include <utmpx.h>
#include <pwd.h>
#include <gio/gio.h>
@ -404,24 +405,12 @@ rounded_rectangle (cairo_t *cr,
cairo_close_path (cr);
}
static guint
get_login_name_max (void)
{
#ifdef LOGIN_NAME_MAX
return LOGIN_NAME_MAX;
#else
static gint length;
if (!length) {
length = sysconf (_SC_LOGIN_NAME_MAX);
g_assert_cmpint (length, >=, 0);
}
return length;
#endif
}
#define MAXNAMELEN get_login_name_max ()
/* Taken from defines.h in shadow-utils. On Linux, this value is much smaller
* than the sysconf limit LOGIN_NAME_MAX, and values larger than this will
* result in failure when running useradd. We could check UT_NAMESIZE instead,
* but that is nonstandard. Better to use POSIX utmpx.
*/
#define MAXNAMELEN (sizeof (((struct utmpx *)NULL)->ut_user))
static gboolean
is_username_used (const gchar *username)