Re: [PATCH] nptl: Zero-extend arguments to SETXID syscalls [BZ #26248]

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Jul 16, 2020 at 7:14 PM Carlos O'Donell <carlos@redhat.com> wrote:
>
> On 7/16/20 5:42 PM, H.J. Lu wrote:
> > On Thu, Jul 16, 2020 at 12:45 PM Aurelien Jarno <aurelien@aurel32.net> wrote:
> >>
> >> On 2020-07-16 05:46, H.J. Lu via Libc-alpha wrote:
> >>> On Thu, Jul 16, 2020 at 5:03 AM Florian Weimer <fweimer@redhat.com> wrote:
> >>>>
> >>>> * H. J. Lu via Libc-alpha:
> >>>>
> >>>>> nptl has
> >>>>>
> >>>>> /* Opcodes and data types for communication with the signal handler to
> >>>>>    change user/group IDs.  */
> >>>>> struct xid_command
> >>>>> {
> >>>>>   int syscall_no;
> >>>>>   long int id[3];
> >>>>>   volatile int cntr;
> >>>>>   volatile int error;
> >>>>> };
> >>>>>
> >>>>>  /* This must be last, otherwise the current thread might not have
> >>>>>      permissions to send SIGSETXID syscall to the other threads.  */
> >>>>>   result = INTERNAL_SYSCALL_NCS (cmdp->syscall_no, 3,
> >>>>>                                  cmdp->id[0], cmdp->id[1], cmdp->id[2]);
> >>>>>
> >>>>> But the second argument of setgroups syscal is a pointer:
> >>>>>
> >>>>>        int setgroups(size_t size, const gid_t *list);
> >>>>>
> >>>>> But on x32, pointers passed to syscall must have pointer type so that they
> >>>>> will be zero-extended.
> >>>>>
> >>>>> Add <setxid-internal.h> to define INTERNAL_SETXID_SYSCALL_NCS and use it,
> >>>>> instead of INTERNAL_SYSCALL_NCS, for SETXID syscalls.  X32 override it
> >>>>> with pointer type for setgroups.  A testcase is added and setgroups
> >>>>> returned with EFAULT when running as root without the fix.
> >>>>
> >>>> Isn't it sufficient to change the type of id to unsigned long int[3]?
> >>>> The UID arguments are unsigned on the kernel side, so no sign extension
> >>>> is required.
> >>>>
> >>>
> >>> It works.  Here is the updated patch.  OK for master?
> >>>
> >>> Thanks.
> >>>
> >>> --
> >>> H.J.
> >>
> >>> From 2af9e56c2306dc9d80a4476fa5b154a26a935557 Mon Sep 17 00:00:00 2001
> >>> From: "H.J. Lu" <hjl.tools@gmail.com>
> >>> Date: Thu, 16 Jul 2020 03:37:10 -0700
> >>> Subject: [PATCH] nptl: Zero-extend arguments to SETXID syscalls [BZ #26248]
> >>>
> >>> nptl has
> >>>
> >>> /* Opcodes and data types for communication with the signal handler to
> >>>    change user/group IDs.  */
> >>> struct xid_command
> >>> {
> >>>   int syscall_no;
> >>>   long int id[3];
> >>>   volatile int cntr;
> >>>   volatile int error;
> >>> };
> >>>
> >>>  /* This must be last, otherwise the current thread might not have
> >>>      permissions to send SIGSETXID syscall to the other threads.  */
> >>>   result = INTERNAL_SYSCALL_NCS (cmdp->syscall_no, 3,
> >>>                                  cmdp->id[0], cmdp->id[1], cmdp->id[2]);
> >>>
> >>> But the second argument of setgroups syscal is a pointer:
> >>>
> >>>        int setgroups(size_t size, const gid_t *list);
> >>>
> >>> But on x32, pointers passed to syscall must have pointer type so that they
> >>> will be zero-extended.  Since the XID arguments are unsigned on the kernel
> >>> side, so no sign extension is required.  Change xid_command to
> >>>
> >>> struct xid_command
> >>> {
> >>>   int syscall_no;
> >>>   unsigned long int id[3];
> >>>   volatile int cntr;
> >>>   volatile int error;
> >>> };
> >>>
> >>> so that all arguments zero-extended.  A testcase is added for x32 and
> >>> setgroups returned with EFAULT when running as root without the fix.
> >>> ---
> >>>  nptl/descr.h                                  |  8 ++-
> >>>  sysdeps/unix/sysv/linux/x86_64/x32/Makefile   |  4 ++
> >>>  .../sysv/linux/x86_64/x32/tst-setgroups.c     | 67 +++++++++++++++++++
> >>>  3 files changed, 78 insertions(+), 1 deletion(-)
> >>>  create mode 100644 sysdeps/unix/sysv/linux/x86_64/x32/tst-setgroups.c
> >>>
> >>> diff --git a/nptl/descr.h b/nptl/descr.h
> >>> index 6a509b6725..e98fe4084d 100644
> >>> --- a/nptl/descr.h
> >>> +++ b/nptl/descr.h
> >>> @@ -95,7 +95,13 @@ struct pthread_unwind_buf
> >>>  struct xid_command
> >>>  {
> >>>    int syscall_no;
> >>> -  long int id[3];
> >>> +  /* Enforce zero-extension for the pointer argument in
> >>> +
> >>> +     int setgroups(size_t size, const gid_t *list);
> >>> +
> >>> +     Since the XID arguments are unsigned on the kernel side, so no sign
> >>> +     extension is required.  */
> >>> +  unsigned long int id[3];
> >>>    volatile int cntr;
> >>>    volatile int error; /* -1: no call yet, 0: success seen, >0: error seen.  */
> >>>  };
> >>> diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/Makefile b/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
> >>> index 16b768d8ba..1a6c984f96 100644
> >>> --- a/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
> >>> +++ b/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
> >>> @@ -5,6 +5,10 @@ ifeq ($(subdir),misc)
> >>>  sysdep_routines += arch_prctl
> >>>  endif
> >>>
> >>> +ifeq ($(subdir),nptl)
> >>> +xtests += tst-setgroups
> >>> +endif
> >>> +
> >>>  ifeq ($(subdir),conform)
> >>>  # For bugs 16437 and 21279.
> >>>  conformtest-xfail-conds += x86_64-x32-linux
> >>> diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/tst-setgroups.c b/sysdeps/unix/sysv/linux/x86_64/x32/tst-setgroups.c
> >>> new file mode 100644
> >>> index 0000000000..9895443278
> >>> --- /dev/null
> >>> +++ b/sysdeps/unix/sysv/linux/x86_64/x32/tst-setgroups.c
> >>> @@ -0,0 +1,67 @@
> >>> +/* Basic test for setgroups
> >>> +   Copyright (C) 2020 Free Software Foundation, Inc.
> >>> +   This file is part of the GNU C Library.
> >>> +
> >>> +   The GNU C Library is free software; you can redistribute it and/or
> >>> +   modify it under the terms of the GNU Lesser General Public
> >>> +   License as published by the Free Software Foundation; either
> >>> +   version 2.1 of the License, or (at your option) any later version.
> >>> +
> >>> +   The GNU C Library is distributed in the hope that it will be useful,
> >>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >>> +   Lesser General Public License for more details.
> >>> +
> >>> +   You should have received a copy of the GNU Lesser General Public
> >>> +   License along with the GNU C Library; if not, see
> >>> +   <https://www.gnu.org/licenses/>.  */
> >>> +
> >>> +#include <stdlib.h>
> >>> +#include <limits.h>
> >>> +#include <grp.h>
> >>> +#include <errno.h>
> >>> +#include <error.h>
> >>> +#include <support/xthread.h>
> >>> +#include <support/support.h>
> >>> +#include <support/test-driver.h>
> >>> +#include <support/xunistd.h>
> >>> +
> >>> +static void *
> >>> +start_routine (void *args)
> >>> +{
> >>> +  return NULL;
> >>> +}
> >>> +
> >>> +static int
> >>> +do_test (void)
> >>> +{
> >>> +  int size;
> >>> +  /* NB: Stack address is at 0xfffXXXXX.  */
> >>> +  gid_t list[NGROUPS_MAX];
> >>> +  int status = EXIT_SUCCESS;
> >>> +
> >>> +  pthread_t thread = xpthread_create (NULL, start_routine, NULL);
> >>> +
> >>> +  size = getgroups (sizeof (list) / sizeof (list[0]), list);
> >>> +  if (size < 0)
> >>> +    {
> >>> +      status = EXIT_FAILURE;
> >>> +      error (0, errno, "getgroups failed");
> >>> +    }
> >>> +  if (setgroups (size, list) < 0)
> >>> +    {
> >>
> >> I guess the idea of using getgroups and setgroups comes from my initial
> >> reproducer in the bug report. But you can actually do simpler by
> >> skipping the getgroups and calling setgroups with a fixed single group.
> >> It correctly handles the case where the list of supplementary groups
> >> returned by getgroups is empty.
> >>
> >
> > This test is simple enough.
> >
> > Carlos, I'd like to get it fixed in 2.32.
>
> Please point me at the final version you want reviewed and I'll do that
> first thing tomorrow morning.
>

Here is the final version:

https://sourceware.org/pipermail/libc-alpha/2020-July/116390.html

-- 
H.J.