[v7] io: Fix ftw internal realloc buffer (BZ #28126)

  The 106ff08526d3ca 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.

---
v7: Move common ftw_data allocate logic to ftw_allocate().

---
 io/Makefile          |  1 +
 io/ftw.c             | 39 +++++++++---------
 io/tst-ftw-bz28126.c | 97 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 117 insertions(+), 20 deletions(-)
 create mode 100644 io/tst-ftw-bz28126.c
  

On Thu, Oct 7, 2021 at 4:18 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> The 106ff08526d3ca 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.
>
> ---
> v7: Move common ftw_data allocate logic to ftw_allocate().
>
> ---
>  io/Makefile          |  1 +
>  io/ftw.c             | 39 +++++++++---------
>  io/tst-ftw-bz28126.c | 97 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 117 insertions(+), 20 deletions(-)
>  create mode 100644 io/tst-ftw-bz28126.c
>
> diff --git a/io/Makefile b/io/Makefile
> index 9871ecbc74..ecf65aba60 100644
> --- a/io/Makefile
> +++ b/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-futimens-time64 \
> diff --git a/io/ftw.c b/io/ftw.c
> index f0db173727..fe953454f2 100644
> --- a/io/ftw.c
> +++ b/io/ftw.c
> @@ -203,6 +203,20 @@ 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'.  */
> @@ -388,17 +402,9 @@ 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';
>
> @@ -628,7 +634,7 @@ __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;
> @@ -646,16 +652,9 @@ 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] == '/')
> diff --git a/io/tst-ftw-bz28126.c b/io/tst-ftw-bz28126.c
> new file mode 100644
> index 0000000000..94044ab9d1
> --- /dev/null
> +++ b/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>
> --
> 2.30.2
>

LGTM.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.