io: Fix ftw internal realloc buffer (BZ #28126)

The 106ff08526 did not take in consideration the buffer might be
reallocated if the total path is larger than PATH_MAX.  The realloc
uses 'dirbuf', where 'dirstreams' is the allocated buffer.

Checked on x86_64-linux-gnu.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit 1836bb2ebf)

NEWS

@@ -65,6 +65,7 @@ The following bugs are resolved with this release:
   [28062] dynamic-link: Suppress audit calls when a (new) namespace is
     empty
   [28096] elf: audit calls that uses static tls might fail
+  [28126] nftw aborts for paths longer than PATH_MAX
   [28182] _TIME_BITS=64 in C++ has issues with fcntl, ioctl, prctl
   [28223] mips: clone does not align stack
   [28310] Do not use affinity mask for sysconf (_SC_NPROCESSORS_CONF)

io/Makefile

@@ -79,6 +79,7 @@ tests		:= test-utime test-stat test-stat2 test-lfs tst-getcwd \
 		   tst-futimens \
 		   tst-utimensat \
 		   tst-closefrom \
+		   tst-ftw-bz28126
 
 tests-time64 := \
   tst-fcntl-time64 \

io/ftw.c

@@ -204,6 +204,20 @@ struct ftw_data
   void *known_objects;
 };
 
+static bool
+ftw_allocate (struct ftw_data *data, size_t newsize)
+{
+  void *newp = realloc (data->dirstreams, data->maxdir
+					  * sizeof (struct dir_data *)
+					  + newsize);
+  if (newp == NULL)
+    return false;
+  data->dirstreams = newp;
+  data->dirbufsize = newsize;
+  data->dirbuf = (char *) data->dirstreams
+		 + data->maxdir * sizeof (struct dir_data *);
+  return true;
+}
 
 /* Internally we use the FTW_* constants used for `nftw'.  When invoked
    as `ftw', map each flag to the subset of values used by `ftw'.  */
@@ -389,17 +403,9 @@ process_entry (struct ftw_data *data, struct dir_data *dir, const char *name,
     return 0;
 
   new_buflen = data->ftw.base + namlen + 2;
-  if (data->dirbufsize < new_buflen)
-    {
-      /* Enlarge the buffer.  */
-      char *newp;
-
-      data->dirbufsize = 2 * new_buflen;
-      newp = (char *) realloc (data->dirbuf, data->dirbufsize);
-      if (newp == NULL)
-	return -1;
-      data->dirbuf = newp;
-    }
+  if (data->dirbufsize < new_buflen
+      && !ftw_allocate (data, 2 * new_buflen))
+    return -1;
 
   *((char *) __mempcpy (data->dirbuf + data->ftw.base, name, namlen)) = '\0';
 
@@ -629,7 +635,7 @@ __attribute ((noinline))
 ftw_startup (const char *dir, int is_nftw, void *func, int descriptors,
 	     int flags)
 {
-  struct ftw_data data;
+  struct ftw_data data = { .dirstreams = NULL };
   struct STRUCT_STAT st;
   int result = 0;
   int save_err;
@@ -647,16 +653,9 @@ ftw_startup (const char *dir, int is_nftw, void *func, int descriptors,
   data.maxdir = descriptors < 1 ? 1 : descriptors;
   data.actdir = 0;
   /* PATH_MAX is always defined when we get here.  */
-  data.dirbufsize = MAX (2 * strlen (dir), PATH_MAX);
-  data.dirstreams = malloc (data.maxdir * sizeof (struct dir_data *)
-                            + data.dirbufsize);
-  if (data.dirstreams == NULL)
+  if (!ftw_allocate (&data, MAX (2 * strlen (dir), PATH_MAX)))
     return -1;
-
   memset (data.dirstreams, '\0', data.maxdir * sizeof (struct dir_data *));
-
-  data.dirbuf = (char *) data.dirstreams
-                + data.maxdir * sizeof (struct dir_data *);
   cp = __stpcpy (data.dirbuf, dir);
   /* Strip trailing slashes.  */
   while (cp > data.dirbuf + 1 && cp[-1] == '/')

io/tst-ftw-bz28126.c

@@ -0,0 +1,97 @@
+/* Check if internal buffer reallocation work for large paths (BZ #28126)
+   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 <errno.h>
+#include <ftw.h>
+#include <limits.h>
+#include <string.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xunistd.h>
+#include <stdio.h>
+
+static int
+my_func (const char *file, const struct stat *sb, int flag)
+{
+  return 0;
+}
+
+static const char folder[NAME_MAX] = { [0 ... 253] = 'a', [254] = '\0' };
+
+#define NSUBFOLDERS 16
+static int nsubfolders;
+
+static void
+do_cleanup (void)
+{
+  xchdir ("..");
+  for (int i = 0; i < nsubfolders; i++)
+    {
+      remove (folder);
+      xchdir ("..");
+    }
+  remove (folder);
+}
+#define CLEANUP_HANDLER do_cleanup
+
+static void
+check_mkdir (const char *path)
+{
+  int r = mkdir (path, 0777);
+  /* Some filesystem such as overlayfs does not support larger path required
+     to trigger the internal buffer reallocation.  */
+  if (r != 0)
+    {
+      if (errno == ENAMETOOLONG)
+	FAIL_UNSUPPORTED ("the filesystem does not support the required"
+			  "large path");
+      else
+	FAIL_EXIT1 ("mkdir (\"%s\", 0%o): %m", folder, 0777);
+    }
+}
+
+static int
+do_test (void)
+{
+  char *tempdir = support_create_temp_directory ("tst-bz28126");
+
+  /* Create path with various subfolders to force an internal buffer
+     reallocation within ntfw.  */
+  char *path = xasprintf ("%s/%s", tempdir, folder);
+  check_mkdir (path);
+  xchdir (path);
+  free (path);
+  for (int i = 0; i < NSUBFOLDERS - 1; i++)
+    {
+      check_mkdir (folder);
+      xchdir (folder);
+      nsubfolders++;
+    }
+
+  TEST_COMPARE (ftw (tempdir, my_func, 20), 0);
+
+  free (tempdir);
+
+  do_cleanup ();
+
+  return 0;
+}
+
+#include <support/test-driver.c>