[v2,1/3] support: Add helpers to create paths longer than PATH_MAX

Add new helpers support_create_and_chdir_toolong_temp_directory and
support_chdir_toolong_temp_directory to create and descend into
directory trees longer than PATH_MAX.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
 support/temp_file.c | 173 +++++++++++++++++++++++++++++++++++++++++---
 support/temp_file.h |   9 +++
 2 files changed, 173 insertions(+), 9 deletions(-)

On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
> Add new helpers support_create_and_chdir_toolong_temp_directory and
> support_chdir_toolong_temp_directory to create and descend into
> directory trees longer than PATH_MAX.
> 
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> ---
>   support/temp_file.c | 173 +++++++++++++++++++++++++++++++++++++++++---
>   support/temp_file.h |   9 +++
>   2 files changed, 173 insertions(+), 9 deletions(-)
> 
> diff --git a/support/temp_file.c b/support/temp_file.c
> index e7bb8aadb9..59060e573f 100644
> --- a/support/temp_file.c
> +++ b/support/temp_file.c
> @@ -1,5 +1,6 @@
>   /* Temporary file handling for tests.
>      Copyright (C) 1998-2022 Free Software Foundation, Inc.
> +   Copyright The GNU Tools Authors.
>      This file is part of the GNU C Library.
>   
>      The GNU C Library is free software; you can redistribute it and/or
> @@ -20,15 +21,17 @@
>      some 32-bit platforms. */
>   #define _FILE_OFFSET_BITS 64
>   
> +#include <support/check.h>
>   #include <support/temp_file.h>
>   #include <support/temp_file-internal.h>
>   #include <support/support.h>
>   
> +#include <errno.h>
>   #include <paths.h>
>   #include <stdio.h>
>   #include <stdlib.h>
>   #include <string.h>
> -#include <unistd.h>
> +#include <xunistd.h>
>   
>   /* List of temporary files.  */
>   static struct temp_name_list
> @@ -36,14 +39,32 @@ static struct temp_name_list
>     struct temp_name_list *next;
>     char *name;
>     pid_t owner;
> +  bool toolong;
>   } *temp_name_list;
>   
>   /* Location of the temporary files.  Set by the test skeleton via
>      support_set_test_dir.  The string is not be freed.  */
>   static const char *test_dir = _PATH_TMP;
>   
> -void
> -add_temp_file (const char *name)
> +/* Name of subdirectories in a too long temporary directory tree.  */
> +static char *toolong_subdir;
> +static bool toolong_subdir_initialized;
> +
> +/* Return the maximum size of path on the target.  */
> +static inline size_t
> +get_path_max (void)
> +{
> +#ifdef PATH_MAX
> +  return PATH_MAX;
> +#else
> +  size_t path_max = pathconf ("/", _PC_PATH_MAX);
> +  return (path_max < 0 ? 1024
> +	  : path_max <= PTRDIFF_MAX ? path_max : PTRDIFF_MAX);
> +#endif
> +}
> +
> +static void
> +add_temp_file_internal (const char *name, bool toolong)
>   {
>     struct temp_name_list *newp
>       = (struct temp_name_list *) xcalloc (sizeof (*newp), 1);
> @@ -53,12 +74,19 @@ add_temp_file (const char *name)
>         newp->name = newname;
>         newp->next = temp_name_list;
>         newp->owner = getpid ();
> +      newp->toolong = toolong;
>         temp_name_list = newp;
>       }
>     else
>       free (newp);
>   }
>   
> +void
> +add_temp_file (const char *name)
> +{
> +  add_temp_file_internal (name, false);
> +}
> +
>   int
>   create_temp_file_in_dir (const char *base, const char *dir, char **filename)
>   {
> @@ -90,8 +118,8 @@ create_temp_file (const char *base, char **filename)
>     return create_temp_file_in_dir (base, test_dir, filename);
>   }
>   
> -char *
> -support_create_temp_directory (const char *base)
> +static char *
> +create_temp_directory_internal (const char *base, bool toolong)
>   {
>     char *path = xasprintf ("%s/%sXXXXXX", test_dir, base);
>     if (mkdtemp (path) == NULL)
> @@ -99,16 +127,132 @@ support_create_temp_directory (const char *base)
>         printf ("error: mkdtemp (\"%s\"): %m", path);
>         exit (1);
>       }
> -  add_temp_file (path);
> +  add_temp_file_internal (path, toolong);
>     return path;
>   }
>   
> -/* Helper functions called by the test skeleton follow.  */
> +char *
> +support_create_temp_directory (const char *base)
> +{
> +  return create_temp_directory_internal (base, false);
> +}
> +
> +static void
> +ensure_toolong_subdir_initialized (void)
> +{
> +  if (!toolong_subdir_initialized)
> +    FAIL_EXIT1 ("uninitialized toolong directory tree\n");
> +}
> +
> +static void
> +initialize_toolong_subdir (void)
> +{
> +  size_t sz = NAME_MAX;
> +  char testname[NAME_MAX];
> +  int ret;
> +
> +  if (toolong_subdir_initialized)
> +    return;
> +
> +  memset (testname, 'X', sz - 1);
> +
> +  /* Explore the name limit on the file system.  This should typically be
> +     NAME_MAX, but it could be less on some fuse filesystems.  */
> +  do
> +    {
> +      struct stat statbuf;
> +
> +      testname[sz - 1] = '\0';
> +      ret = stat (testname, &statbuf);
> +    }
> +  while (ret != 0 && errno == ENAMETOOLONG && (sz = sz / 2) > 0);
> +
> +  if (ret != 0 && errno == ENAMETOOLONG)
> +    FAIL_EXIT1 ("stat (%s) failed with ENAMETOOLONG\n", testname);
> +
> +  toolong_subdir = xmalloc (sz);
> +  strcpy (toolong_subdir, testname);
> +  toolong_subdir_initialized = true;
> +}
> +
> +char *
> +support_create_and_chdir_toolong_temp_directory (const char *basename)
> +{
> +  size_t path_max = get_path_max ();
> +
> +  char *base = create_temp_directory_internal (basename, true);
> +
> +  xchdir (base);
> +
> +  initialize_toolong_subdir ();
> +
> +  size_t sz = strlen (toolong_subdir);
> +
> +  /* Create directories and descend into them so that the final path is larger
> +     than PATH_MAX.  */
> +  for (size_t i = 0; i <= path_max / sz; i++)
> +    {
> +      xmkdir (toolong_subdir, S_IRWXU);

This still doesn't work on the trybot, which somehow fails with 
ENAMETOOLONG even though stat() on that length worked in 
initialize_toolong_subdir.  I'm going to need to reproduce the 
environment properly to figure out what's going on.

Siddhesh

> +      xchdir (toolong_subdir);
> +    }
> +  return base;
> +}
>   
>   void
> -support_set_test_dir (const char *path)
> +support_chdir_toolong_temp_directory (const char *base)
>   {
> -  test_dir = path;
> +  size_t path_max = get_path_max ();
> +  ensure_toolong_subdir_initialized ();
> +
> +  xchdir (base);
> +
> +  size_t sz = strlen (toolong_subdir);
> +  for (size_t i = 0; i <= path_max / sz; i++)
> +    xchdir (toolong_subdir);
> +}
> +
> +/* Helper functions called by the test skeleton follow.  */
> +
> +static void
> +remove_toolong_subdirs (const char *base)
> +{
> +  size_t path_max = get_path_max ();
> +
> +  ensure_toolong_subdir_initialized ();
> +
> +  if (chdir (base) != 0)
> +    {
> +      printf ("warning: toolong cleanup base failed: chdir (\"%s\"): %m\n",
> +	      base);
> +      return;
> +    }
> +
> +  /* Descend.  */
> +  int levels = 0;
> +  size_t sz = strlen (toolong_subdir);
> +  for (levels = 0; levels <= path_max / sz; levels++)
> +    if (chdir (toolong_subdir) != 0)
> +      {
> +	printf ("warning: toolong cleanup failed: chdir (\"%s\"): %m\n",
> +		toolong_subdir);
> +	return;
> +      }
> +
> +  /* Ascend and remove.  */
> +  while (--levels >= 0)
> +    {
> +      if (chdir ("..") != 0)
> +	{
> +	  printf ("warning: toolong cleanup failed: chdir (\"..\"): %m\n");
> +	  return;
> +	}
> +      if (remove (toolong_subdir) != 0)
> +	{
> +	  printf ("warning: could not remove subdirectory: %s: %m\n",
> +		  toolong_subdir);
> +	  return;
> +	}
> +    }
>   }
>   
>   void
> @@ -123,6 +267,9 @@ support_delete_temp_files (void)
>   	 around, to prevent PID reuse.)  */
>         if (temp_name_list->owner == pid)
>   	{
> +	  if (temp_name_list->toolong)
> +	    remove_toolong_subdirs (temp_name_list->name);
> +
>   	  if (remove (temp_name_list->name) != 0)
>   	    printf ("warning: could not remove temporary file: %s: %m\n",
>   		    temp_name_list->name);
> @@ -133,6 +280,8 @@ support_delete_temp_files (void)
>         free (temp_name_list);
>         temp_name_list = next;
>       }
> +
> +  free (toolong_subdir);
>   }
>   
>   void
> @@ -147,3 +296,9 @@ support_print_temp_files (FILE *f)
>         fprintf (f, ")\n");
>       }
>   }
> +
> +void
> +support_set_test_dir (const char *path)
> +{
> +  test_dir = path;
> +}
> diff --git a/support/temp_file.h b/support/temp_file.h
> index 50a443abe4..8459ddda72 100644
> --- a/support/temp_file.h
> +++ b/support/temp_file.h
> @@ -44,6 +44,15 @@ int create_temp_file_in_dir (const char *base, const char *dir,
>      returns.  The caller should free this string.  */
>   char *support_create_temp_directory (const char *base);
>   
> +/* Create a temporary directory tree that is longer than PATH_MAX and schedule
> +   it for deletion.  BASENAME is used as a prefix for the unique directory
> +   name, which the function returns.  The caller should free this string.  */
> +char *support_create_and_chdir_toolong_temp_directory (const char *basename);
> +
> +/* Change into the innermost directory of the directory tree BASE, which was
> +   created using support_create_and_chdir_toolong_temp_directory.  */
> +void support_chdir_toolong_temp_directory (const char *base);
> +
>   __END_DECLS
>   
>   #endif /* SUPPORT_TEMP_FILE_H */

On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>
> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
> > Add new helpers support_create_and_chdir_toolong_temp_directory and
> > support_chdir_toolong_temp_directory to create and descend into
> > directory trees longer than PATH_MAX.

Note that recentish linux kernel versions do not allow d_name 's
larger than kernel 's PATH_MAX definition, in that case getdents
returns EIO, this behavior is since kernel 5.5.

* Cristian Rodríguez:

> On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>>
>> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
>> > Add new helpers support_create_and_chdir_toolong_temp_directory and
>> > support_chdir_toolong_temp_directory to create and descend into
>> > directory trees longer than PATH_MAX.
>
> Note that recentish linux kernel versions do not allow d_name 's
> larger than kernel 's PATH_MAX definition, in that case getdents
> returns EIO, this behavior is since kernel 5.5.

NAME_MAX or PATH_MAX?  d_name should be capped by NAME_MAX, but
historically it is not.

Thanks,
Florian

On 20/01/2022 20:17, Cristian Rodríguez wrote:
> On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>>
>> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
>>> Add new helpers support_create_and_chdir_toolong_temp_directory and
>>> support_chdir_toolong_temp_directory to create and descend into
>>> directory trees longer than PATH_MAX.
> 
> Note that recentish linux kernel versions do not allow d_name 's
> larger than kernel 's PATH_MAX definition, in that case getdents
> returns EIO, this behavior is since kernel 5.5.
> 

The d_name in these helpers is limited to _PC_NAME_MAX so AFAICT we 
shouldn't run into issues with that.

Thanks,
Siddhesh

On Thu, Jan 20, 2022 at 11:56 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Cristian Rodríguez:
>
> > On Wed, Jan 19, 2022 at 7:21 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
> >>
> >> On 19/01/2022 13:51, Siddhesh Poyarekar via Libc-alpha wrote:
> >> > Add new helpers support_create_and_chdir_toolong_temp_directory and
> >> > support_chdir_toolong_temp_directory to create and descend into
> >> > directory trees longer than PATH_MAX.
> >
> > Note that recentish linux kernel versions do not allow d_name 's
> > larger than kernel 's PATH_MAX definition, in that case getdents
> > returns EIO, this behavior is since kernel 5.5.
>
> NAME_MAX or PATH_MAX?  d_name should be capped by NAME_MAX, but
> historically it is not.

PATH_MAX.. I wrote that correctly,  see
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2c6b7bcd747201441923a0d3062577a8d1fbd8f8