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

Now that fstat is implemented on top fstatat we need to handle negative
inputs.  The implementation now rejects AT_FDCWD, which would otherwise
be accepted by the kernel.

Checked on x86_64-linux-gnu and on i686-linux-gnu.

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

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);
 }
 

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)

io/tst-stat-lfs.c

@@ -0,0 +1,2 @@
+#define _FILE_OFFSET_BITS 64
+#include "tst-stat.c"

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>

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);
 }
 

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);