[PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[Adhemerval Zanella]

Now that fstat is implemented on top fstatat we need to handle negative
inputs.

Checked on x86_64-linux-gnu and on i686-linux-gnu.
---
 io/Makefile                       |   2 +-
 io/fstat.c                        |   6 ++
 io/fstat64.c                      |   6 ++
 io/tst-stat.c                     | 102 ++++++++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/fstat.c   |   6 ++
 sysdeps/unix/sysv/linux/fstat64.c |  12 ++++
 6 files changed, 133 insertions(+), 1 deletion(-)
 create mode 100644 io/tst-stat.c

diff --git a/io/Makefile b/io/Makefile
index b7bebe923f..d145d88f4e 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -68,7 +68,7 @@ tests		:= test-utime test-stat test-stat2 test-lfs tst-getcwd \
 		   tst-fts tst-fts-lfs tst-open-tmpfile \
 		   tst-copy_file_range tst-getcwd-abspath tst-lockf \
 		   tst-ftw-lnk tst-file_change_detection tst-lchmod \
-		   tst-ftw-bz26353
+		   tst-ftw-bz26353 tst-stat tst-stat-lfs
 
 # Likewise for statx, but we do not need static linking here.
 tests-internal += tst-statx
diff --git a/io/fstat.c b/io/fstat.c
index dc117361ff..17f31bf3b3 100644
--- a/io/fstat.c
+++ b/io/fstat.c
@@ -16,10 +16,16 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <sys/stat.h>
+#include <errno.h>
 
 int
 __fstat (int fd, struct stat *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
   return __fstatat (fd, "", buf, AT_EMPTY_PATH);
 }
 
diff --git a/io/fstat64.c b/io/fstat64.c
index addf379775..618170695c 100644
--- a/io/fstat64.c
+++ b/io/fstat64.c
@@ -16,10 +16,16 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <sys/stat.h>
+#include <errno.h>
 
 int
 __fstat64 (int fd, struct stat64 *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
   return __fstatat64 (fd, "", buf, AT_EMPTY_PATH);
 }
 hidden_def (__fstat64)
diff --git a/io/tst-stat.c b/io/tst-stat.c
new file mode 100644
index 0000000000..445ac4176c
--- /dev/null
+++ b/io/tst-stat.c
@@ -0,0 +1,102 @@
+/* Basic tests for stat, lstat, fstat, and fstatat.
+   Copyright (C) 2021 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 <array_length.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xunistd.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+#include <unistd.h>
+
+static void
+stat_check (int fd, const char *path, struct stat *st)
+{
+  TEST_COMPARE (stat (path, st), 0);
+}
+
+static void
+lstat_check (int fd, const char *path, struct stat *st)
+{
+  TEST_COMPARE (lstat (path, st), 0);
+}
+
+static void
+fstat_check (int fd, const char *path, struct stat *st)
+{
+  /* Test for invalid fstat input (BZ #27559).  */
+  TEST_COMPARE (fstat (AT_FDCWD, st), -1);
+  TEST_COMPARE (errno, EBADF);
+
+  TEST_COMPARE (fstat (fd, st), 0);
+}
+
+static void
+fstatat_check (int fd, const char *path, struct stat *st)
+{
+  TEST_COMPARE (fstatat (fd, "", st, 0), -1);
+  TEST_COMPARE (errno, ENOENT);
+
+  TEST_COMPARE (fstatat (fd, path, st, 0), 0);
+}
+
+typedef void (*test_t)(int, const char *path, struct stat *);
+
+static int
+do_test (void)
+{
+  char *path;
+  int fd = create_temp_file ("tst-fstat.", &path);
+  TEST_VERIFY_EXIT (fd >= 0);
+  support_write_file_string (path, "abc");
+
+  struct statx stx;
+  TEST_COMPARE (statx (fd, path, 0, STATX_BASIC_STATS, &stx), 0);
+
+  test_t tests[] = { stat_check, lstat_check, fstat_check, fstatat_check };
+
+  for (int i = 0; i < array_length (tests); i++)
+    {
+      struct stat st;
+      tests[i](fd, path, &st);
+
+      TEST_COMPARE (stx.stx_dev_major, major (st.st_dev));
+      TEST_COMPARE (stx.stx_dev_minor, minor (st.st_dev));
+      TEST_COMPARE (stx.stx_ino, st.st_ino);
+      TEST_COMPARE (stx.stx_mode, st.st_mode);
+      TEST_COMPARE (stx.stx_nlink, st.st_nlink);
+      TEST_COMPARE (stx.stx_uid, st.st_uid);
+      TEST_COMPARE (stx.stx_gid, st.st_gid);
+      TEST_COMPARE (stx.stx_rdev_major, major (st.st_rdev));
+      TEST_COMPARE (stx.stx_rdev_minor, minor (st.st_rdev));
+      TEST_COMPARE (stx.stx_blksize, st.st_blksize);
+      TEST_COMPARE (stx.stx_blocks, st.st_blocks);
+
+      TEST_COMPARE (stx.stx_ctime.tv_sec, st.st_ctim.tv_sec);
+      TEST_COMPARE (stx.stx_ctime.tv_nsec, st.st_ctim.tv_nsec);
+      TEST_COMPARE (stx.stx_mtime.tv_sec, st.st_mtim.tv_sec);
+      TEST_COMPARE (stx.stx_mtime.tv_nsec, st.st_mtim.tv_nsec);
+    }
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/fstat.c b/sysdeps/unix/sysv/linux/fstat.c
index fd64362205..31a172dcc8 100644
--- a/sysdeps/unix/sysv/linux/fstat.c
+++ b/sysdeps/unix/sysv/linux/fstat.c
@@ -19,11 +19,17 @@
 #include <sys/stat.h>
 #include <kernel_stat.h>
 #include <fcntl.h>
+#include <errno.h>
 
 #if !XSTAT_IS_XSTAT64
 int
 __fstat (int fd, struct stat *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
   return __fstatat (fd, "", buf, AT_EMPTY_PATH);
 }
 
diff --git a/sysdeps/unix/sysv/linux/fstat64.c b/sysdeps/unix/sysv/linux/fstat64.c
index 993abcb445..46de80b663 100644
--- a/sysdeps/unix/sysv/linux/fstat64.c
+++ b/sysdeps/unix/sysv/linux/fstat64.c
@@ -22,10 +22,16 @@
 #include <fcntl.h>
 #include <kernel_stat.h>
 #include <stat_t64_cp.h>
+#include <errno.h>
 
 int
 __fstat64_time64 (int fd, struct __stat64_t64 *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
   return __fstatat64_time64 (fd, "", buf, AT_EMPTY_PATH);
 }
 #if __TIMESIZE != 64
@@ -34,6 +40,12 @@ hidden_def (__fstat64_time64)
 int
 __fstat64 (int fd, struct stat64 *buf)
 {
+  if (fd < 0)
+    {
+      __set_errno (EBADF);
+      return -1;
+    }
+
   struct __stat64_t64 st_t64;
   return __fstat64_time64 (fd, &st_t64)
 	 ?: __cp_stat64_t64_stat64 (&st_t64, buf);
-- 
2.25.1

Re: [PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[Florian Weimer]

* Adhemerval Zanella via Libc-alpha:

> Now that fstat is implemented on top fstatat we need to handle negative
> inputs.

Please mention AT_FDCWD in the commit message.  Or add a comment to the
code that the check rejects AT_FDCWD, which would otherwise be accepted
by the kernel.

The patch looks okay otherwise.

Thanks,
Florian

Re: [PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[Adhemerval Zanella]

On 11/03/2021 09:13, Florian Weimer wrote:
> * Adhemerval Zanella via Libc-alpha:
> 
>> Now that fstat is implemented on top fstatat we need to handle negative
>> inputs.
> 
> Please mention AT_FDCWD in the commit message.  Or add a comment to the
> code that the check rejects AT_FDCWD, which would otherwise be accepted
> by the kernel.
> 
> The patch looks okay otherwise.

Ack.  I will also add the missing tst-stat-lfs (which is just a wrapper
to set __FILE_OFFSET_BITS=64).

Re: [PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[Stefan Liebler]

On 3/11/21 1:37 PM, Adhemerval Zanella via Libc-alpha wrote:
> 
> 
> On 11/03/2021 09:13, Florian Weimer wrote:
>> * Adhemerval Zanella via Libc-alpha:
>>
>>> Now that fstat is implemented on top fstatat we need to handle negative
>>> inputs.
>>
>> Please mention AT_FDCWD in the commit message.  Or add a comment to the
>> code that the check rejects AT_FDCWD, which would otherwise be accepted
>> by the kernel.
>>
>> The patch looks okay otherwise.
> 
> Ack.  I will also add the missing tst-stat-lfs (which is just a wrapper
> to set __FILE_OFFSET_BITS=64).
> 

Hi Adhemerval,

I've just recognized that io/tst-stat is failing on my s390 (31bit) system:
tst-stat.c:94: numeric comparison failure

   left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec

  right: 0 (0x0); from: st.st_ctim.tv_nsec

tst-stat.c:96: numeric comparison failure

   left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
  right: 0 (0x0); from: st.st_mtim.tv_nsec
tst-stat.c:94: numeric comparison failure
   left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
  right: 0 (0x0); from: st.st_ctim.tv_nsec
tst-stat.c:96: numeric comparison failure
   left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
  right: 0 (0x0); from: st.st_mtim.tv_nsec
tst-stat.c:94: numeric comparison failure
   left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
  right: 0 (0x0); from: st.st_ctim.tv_nsec
tst-stat.c:96: numeric comparison failure
   left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
  right: 0 (0x0); from: st.st_mtim.tv_nsec
tst-stat.c:94: numeric comparison failure
   left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
  right: 0 (0x0); from: st.st_ctim.tv_nsec
tst-stat.c:96: numeric comparison failure
   left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
  right: 0 (0x0); from: st.st_mtim.tv_nsec
error: 8 test failures


But I have to admit, I haven't looked into the test yet and won't be
able before next week. But I wanted to report it now.

Bye,
Stefan

Re: [PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[Adhemerval Zanella]

On 12/03/2021 10:44, Stefan Liebler wrote:
> On 3/11/21 1:37 PM, Adhemerval Zanella via Libc-alpha wrote:
>>
>>
>> On 11/03/2021 09:13, Florian Weimer wrote:
>>> * Adhemerval Zanella via Libc-alpha:
>>>
>>>> Now that fstat is implemented on top fstatat we need to handle negative
>>>> inputs.
>>>
>>> Please mention AT_FDCWD in the commit message.  Or add a comment to the
>>> code that the check rejects AT_FDCWD, which would otherwise be accepted
>>> by the kernel.
>>>
>>> The patch looks okay otherwise.
>>
>> Ack.  I will also add the missing tst-stat-lfs (which is just a wrapper
>> to set __FILE_OFFSET_BITS=64).
>>
> 
> Hi Adhemerval,
> 
> I've just recognized that io/tst-stat is failing on my s390 (31bit) system:
> tst-stat.c:94: numeric comparison failure
> 
>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
> 
>   right: 0 (0x0); from: st.st_ctim.tv_nsec
> 
> tst-stat.c:96: numeric comparison failure
> 
>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>   right: 0 (0x0); from: st.st_mtim.tv_nsec
> tst-stat.c:94: numeric comparison failure
>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>   right: 0 (0x0); from: st.st_ctim.tv_nsec
> tst-stat.c:96: numeric comparison failure
>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>   right: 0 (0x0); from: st.st_mtim.tv_nsec
> tst-stat.c:94: numeric comparison failure
>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>   right: 0 (0x0); from: st.st_ctim.tv_nsec
> tst-stat.c:96: numeric comparison failure
>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>   right: 0 (0x0); from: st.st_mtim.tv_nsec
> tst-stat.c:94: numeric comparison failure
>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>   right: 0 (0x0); from: st.st_ctim.tv_nsec
> tst-stat.c:96: numeric comparison failure
>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>   right: 0 (0x0); from: st.st_mtim.tv_nsec
> error: 8 test failures
> 
> 
> But I have to admit, I haven't looked into the test yet and won't be
> able before next week. But I wanted to report it now.
> 
> Bye,
> Stefan


I will check this out on a s390 system.

Re: [PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[Adhemerval Zanella]

On 12/03/2021 10:57, Adhemerval Zanella wrote:
> 
> 
> On 12/03/2021 10:44, Stefan Liebler wrote:
>> On 3/11/21 1:37 PM, Adhemerval Zanella via Libc-alpha wrote:
>>>
>>>
>>> On 11/03/2021 09:13, Florian Weimer wrote:
>>>> * Adhemerval Zanella via Libc-alpha:
>>>>
>>>>> Now that fstat is implemented on top fstatat we need to handle negative
>>>>> inputs.
>>>>
>>>> Please mention AT_FDCWD in the commit message.  Or add a comment to the
>>>> code that the check rejects AT_FDCWD, which would otherwise be accepted
>>>> by the kernel.
>>>>
>>>> The patch looks okay otherwise.
>>>
>>> Ack.  I will also add the missing tst-stat-lfs (which is just a wrapper
>>> to set __FILE_OFFSET_BITS=64).
>>>
>>
>> Hi Adhemerval,
>>
>> I've just recognized that io/tst-stat is failing on my s390 (31bit) system:
>> tst-stat.c:94: numeric comparison failure
>>
>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>
>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>>
>> tst-stat.c:96: numeric comparison failure
>>
>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>> tst-stat.c:94: numeric comparison failure
>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>> tst-stat.c:96: numeric comparison failure
>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>> tst-stat.c:94: numeric comparison failure
>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>> tst-stat.c:96: numeric comparison failure
>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>> tst-stat.c:94: numeric comparison failure
>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>> tst-stat.c:96: numeric comparison failure
>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>> error: 8 test failures
>>
>>
>> But I have to admit, I haven't looked into the test yet and won't be
>> able before next week. But I wanted to report it now.
>>
>> Bye,
>> Stefan
> 
> 
> I will check this out on a s390 system.
> 

I think we stumbled on another kernel limitation/issue: the tst-stat uses
the __NR_fstatat64 call that for s390 will use the entrypoint:

arch/s390/kernel/compat_linux.c:

150 COMPAT_SYSCALL_DEFINE2(s390_stat64, const char __user *, filename, struct stat64_emu31 __user *, statbuf)
151 {
152         struct kstat stat;
153         int ret = vfs_stat(filename, &stat);
154         if (!ret)
155                 ret = cp_stat64(statbuf, &stat);
156         return ret;
157 }

And the cp_stat64 explicit omit the nanoseconds fields:

126 static int cp_stat64(struct stat64_emu31 __user *ubuf, struct kstat *stat)
127 {       
128         struct stat64_emu31 tmp;
129         
130         memset(&tmp, 0, sizeof(tmp));
131         
132         tmp.st_dev = huge_encode_dev(stat->dev);
133         tmp.st_ino = stat->ino;
134         tmp.__st_ino = (u32)stat->ino;
135         tmp.st_mode = stat->mode;
136         tmp.st_nlink = (unsigned int)stat->nlink;
137         tmp.st_uid = from_kuid_munged(current_user_ns(), stat->uid);
138         tmp.st_gid = from_kgid_munged(current_user_ns(), stat->gid);
139         tmp.st_rdev = huge_encode_dev(stat->rdev);
140         tmp.st_size = stat->size;
141         tmp.st_blksize = (u32)stat->blksize;
142         tmp.st_blocks = (u32)stat->blocks;
143         tmp.st_atime = (u32)stat->atime.tv_sec;
144         tmp.st_mtime = (u32)stat->mtime.tv_sec;
145         tmp.st_ctime = (u32)stat->ctime.tv_sec;
146         
147         return copy_to_user(ubuf,&tmp,sizeof(tmp)) ? -EFAULT : 0;
148 }

It seems deliberated from a comment that hits the idea was to in the
future to use the __pad[6,7,8] (meant to nanoseconds) as the high 
bits for the seconds part.

The straightforward fix would to just disable the nanoseconds check
for non-lfs interface.  For LFS interface s390 will use statx as
other architectures, which should mitigate the issue on recent
kernels.

Re: [PATCH] io: Return EBAFD for negative file descriptor on fstat (BZ #27559)

[Stefan Liebler]

On 12/03/2021 15:21, Adhemerval Zanella wrote:
> 
> 
> On 12/03/2021 10:57, Adhemerval Zanella wrote:
>>
>>
>> On 12/03/2021 10:44, Stefan Liebler wrote:
>>> On 3/11/21 1:37 PM, Adhemerval Zanella via Libc-alpha wrote:
>>>>
>>>>
>>>> On 11/03/2021 09:13, Florian Weimer wrote:
>>>>> * Adhemerval Zanella via Libc-alpha:
>>>>>
>>>>>> Now that fstat is implemented on top fstatat we need to handle negative
>>>>>> inputs.
>>>>>
>>>>> Please mention AT_FDCWD in the commit message.  Or add a comment to the
>>>>> code that the check rejects AT_FDCWD, which would otherwise be accepted
>>>>> by the kernel.
>>>>>
>>>>> The patch looks okay otherwise.
>>>>
>>>> Ack.  I will also add the missing tst-stat-lfs (which is just a wrapper
>>>> to set __FILE_OFFSET_BITS=64).
>>>>
>>>
>>> Hi Adhemerval,
>>>
>>> I've just recognized that io/tst-stat is failing on my s390 (31bit) system:
>>> tst-stat.c:94: numeric comparison failure
>>>
>>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>>
>>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>>>
>>> tst-stat.c:96: numeric comparison failure
>>>
>>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>>> tst-stat.c:94: numeric comparison failure
>>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>>> tst-stat.c:96: numeric comparison failure
>>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>>> tst-stat.c:94: numeric comparison failure
>>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>>> tst-stat.c:96: numeric comparison failure
>>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>>> tst-stat.c:94: numeric comparison failure
>>>    left: 315117680 (0x12c85070); from: stx.stx_ctime.tv_nsec
>>>   right: 0 (0x0); from: st.st_ctim.tv_nsec
>>> tst-stat.c:96: numeric comparison failure
>>>    left: 315117680 (0x12c85070); from: stx.stx_mtime.tv_nsec
>>>   right: 0 (0x0); from: st.st_mtim.tv_nsec
>>> error: 8 test failures
>>>
>>>
>>> But I have to admit, I haven't looked into the test yet and won't be
>>> able before next week. But I wanted to report it now.
>>>
>>> Bye,
>>> Stefan
>>
>>
>> I will check this out on a s390 system.
>>
> 
> I think we stumbled on another kernel limitation/issue: the tst-stat uses
> the __NR_fstatat64 call that for s390 will use the entrypoint:
> 
> arch/s390/kernel/compat_linux.c:
> 
> 150 COMPAT_SYSCALL_DEFINE2(s390_stat64, const char __user *, filename, struct stat64_emu31 __user *, statbuf)
> 151 {
> 152         struct kstat stat;
> 153         int ret = vfs_stat(filename, &stat);
> 154         if (!ret)
> 155                 ret = cp_stat64(statbuf, &stat);
> 156         return ret;
> 157 }
> 
> And the cp_stat64 explicit omit the nanoseconds fields:
> 
> 126 static int cp_stat64(struct stat64_emu31 __user *ubuf, struct kstat *stat)
> 127 {       
> 128         struct stat64_emu31 tmp;
> 129         
> 130         memset(&tmp, 0, sizeof(tmp));
> 131         
> 132         tmp.st_dev = huge_encode_dev(stat->dev);
> 133         tmp.st_ino = stat->ino;
> 134         tmp.__st_ino = (u32)stat->ino;
> 135         tmp.st_mode = stat->mode;
> 136         tmp.st_nlink = (unsigned int)stat->nlink;
> 137         tmp.st_uid = from_kuid_munged(current_user_ns(), stat->uid);
> 138         tmp.st_gid = from_kgid_munged(current_user_ns(), stat->gid);
> 139         tmp.st_rdev = huge_encode_dev(stat->rdev);
> 140         tmp.st_size = stat->size;
> 141         tmp.st_blksize = (u32)stat->blksize;
> 142         tmp.st_blocks = (u32)stat->blocks;
> 143         tmp.st_atime = (u32)stat->atime.tv_sec;
> 144         tmp.st_mtime = (u32)stat->mtime.tv_sec;
> 145         tmp.st_ctime = (u32)stat->ctime.tv_sec;
> 146         
> 147         return copy_to_user(ubuf,&tmp,sizeof(tmp)) ? -EFAULT : 0;
> 148 }
> 
> It seems deliberated from a comment that hits the idea was to in the
> future to use the __pad[6,7,8] (meant to nanoseconds) as the high 
> bits for the seconds part.
> 
> The straightforward fix would to just disable the nanoseconds check
> for non-lfs interface.  For LFS interface s390 will use statx as
> other architectures, which should mitigate the issue on recent
> kernels.
> 

Hi Adhemerval,

thanks very much for looking into it.
I've just posted this patch:
"[PATCH] Don't test nanoseconds for non-LFS interface in io/tst-stat.c"
https://sourceware.org/pipermail/libc-alpha/2021-March/123943.html

Thanks,
Stefan