Re: [PATCH][BZ 17251] Calculate RPATH $ORIGIN from absolute path

[Brennan Shacklett <bpshacklett at gmail dot com>]

ping

On Mon, Oct 6, 2014 at 9:18 AM, Brennan Shacklett <bpshacklett@gmail.com> wrote:
> ping
>
> On Wed, Oct 1, 2014 at 12:28 AM, Brennan Shacklett
> <bpshacklett@gmail.com> wrote:
>> ping
>>
>> On Tue, Sep 23, 2014 at 8:09 PM, Brennan Shacklett
>> <bpshacklett@gmail.com> wrote:
>>> On Tue, Aug 12, 2014 at 9:16 AM, Brennan Shacklett
>>> <bpshacklett@gmail.com> wrote:
>>>> Bug 17251 deals with (what I believe is) the incorrect calculation of $ORIGIN
>>>> for shared libraries. Currently $ORIGIN is calculated correctly for executables
>>>> on linux, because readlink is called on /proc/self/exe, which means the
>>>> resulting path is absolute and has no symlinks.
>>>> Shared libraries with relative paths on the other hand are based
>>>> off of appending the name / path of the library to the current working
>>>> directory, which means if the library is a symlink, it is not followed, which
>>>> breaks RPATH $ORIGIN in the following scenario:
>>>>
>>>> libone.so and libtwo.so are both in ~/lib
>>>> libone.so needs libtwo.so, so libone.so has an RPATH of $ORIGIN.
>>>> If I run ldd on ~/lib/libone.so, libtwo.so is found and all is good.
>>>> If I create a symlink named ~/libone.so to ~/lib/libone.so, and run ldd on it
>>>> libtwo is not found, because $ORIGIN for the library is calculated as ~
>>>> instead of ~/lib.
>>>>
>>>> If I was to repeat the above test but instead of libone.so use an executable,
>>>> everything would work as expected, which is why I think the shared library
>>>> behavior is a bug.
>>>>
>>>> I ran into this in the real world when attempting to dynamically load a .so
>>>> for python SWIG bindings, because the .so which python was loading was
>>>> symlinked to the actual library directory where all of the .so's dependencies
>>>> were located.
>>>>
>>>> The attached patch fixes this behavior by having realname evaluated with
>>>> __realpath in _dl_map_object_from_fd, before _dl_new_object is called (which is
>>>> where l_origin is assigned). This also somewhat simplifies the code in
>>>> elf/dl-object.c, because realname is guaranteed to be an absolute path
>>>> generated by realpath, so I was able to remove the code dealing with relative
>>>> paths.
>>>> I used the implementation of dl_realpath from sysdeps/tile/dl-runtime.c as the
>>>> generic implementation, and extended it with lstat and readlink in the linux
>>>> version. This means the bug is still present on other systems than linux (the
>>>> generic implementation only returns an absolute path, it doesn't do anything
>>>> with symlinks), but if there is a way to get the generic version to follow
>>>> symlinks on all systems please let me know.
>>>>
>>>> I tested and ran the elf test suite on Gentoo Linux x86-64. If this change is
>>>> wanted, I will happily write a test to go along with it.
>>>> I don't have any sort of copyright attribution set up with the FSF, let me know
>>>> if it is necessary for this change.
>>>>
>>>> Thanks,
>>>> Brennan Shacklett
>>>>
>>>> 2014-08-12  Brennan Shacklett  <bpshacklett@gmail.com>
>>>>
>>>>         [BZ #17251]
>>>>         * elf/Makefile (rtld-routines): Add dl-realpath.
>>>>         * elf/dl-load.c (_dl_map_object_from_fd):
>>>>         Calculate realname with __realpath.
>>>>         * elf/dl-object.c (_dl_new_object): Remove relative path handling.
>>>>         * elf/dl-realpath.c: New file. Generic implementation of __realpath.
>>>>         * elf/tile/dl-runtime.c (_dl_after_load): Remove dl_realpath and
>>>>         change call to __realpath.
>>>>         * sysdeps/unix/sysv/linux/Makefile (sysdep-rtld-routines):
>>>>         Add dl-lxstat64.
>>>>         * sysdeps/unix/sysv/linux/dl-lxstat64.c: New file.
>>>>         * sysdeps/unix/sysv/linux/dl-realpath.c: New file. Handle symlinks
>>>>         unlike generic implementation.
>>>> ---
>>>>  elf/Makefile                          |   3 +-
>>>>  elf/dl-load.c                         |  18 +++++
>>>>  elf/dl-object.c                       |  54 ++-------------
>>>>  elf/dl-realpath.c                     |  85 ++++++++++++++++++++++++
>>>>  sysdeps/tile/dl-runtime.c             |  66 +------------------
>>>>  sysdeps/unix/sysv/linux/Makefile      |   2 +-
>>>>  sysdeps/unix/sysv/linux/dl-lxstat64.c |   1 +
>>>>  sysdeps/unix/sysv/linux/dl-realpath.c | 121 ++++++++++++++++++++++++++++++++++
>>>>  8 files changed, 236 insertions(+), 114 deletions(-)
>>>>  create mode 100644 elf/dl-realpath.c
>>>>  create mode 100644 sysdeps/unix/sysv/linux/dl-lxstat64.c
>>>>  create mode 100644 sysdeps/unix/sysv/linux/dl-realpath.c
>>>>
>>>> diff --git a/elf/Makefile b/elf/Makefile
>>>> index 25012cc..c130f21 100644
>>>> --- a/elf/Makefile
>>>> +++ b/elf/Makefile
>>>> @@ -43,7 +43,8 @@ shared-only-routines += dl-caller
>>>>
>>>>  # ld.so uses those routines, plus some special stuff for being the program
>>>>  # interpreter and operating independent of libc.
>>>> -rtld-routines  := rtld $(dl-routines) dl-sysdep dl-environ dl-minimal
>>>> +rtld-routines  := rtld $(dl-routines) dl-sysdep dl-environ dl-minimal \
>>>> +                  dl-realpath
>>>>  all-rtld-routines = $(rtld-routines) $(sysdep-rtld-routines)
>>>>
>>>>  CFLAGS-dl-runtime.c = -fexceptions -fasynchronous-unwind-tables
>>>> diff --git a/elf/dl-load.c b/elf/dl-load.c
>>>> index 016a99c..7353837 100644
>>>> --- a/elf/dl-load.c
>>>> +++ b/elf/dl-load.c
>>>> @@ -891,6 +891,7 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
>>>>    int errval = 0;
>>>>    struct r_debug *r = _dl_debug_initialize (0, nsid);
>>>>    bool make_consistent = false;
>>>> +  char *absolutename = NULL;
>>>>
>>>>    /* Get file information.  */
>>>>    if (__glibc_unlikely (__fxstat64 (_STAT_VER, fd, &st) < 0))
>>>> @@ -902,6 +903,23 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
>>>>        lose (errval, fd, name, realname, l, errstring,
>>>>             make_consistent ? r : NULL, nsid);
>>>>      }
>>>> +  /* Find absolute pathname for object */
>>>> +  absolutename = (char *) malloc (PATH_MAX);
>>>> +  if (!absolutename)
>>>> +    {
>>>> +      errstring = N_("cannot allocate memory for absolute path");
>>>> +      goto call_lose_errno;
>>>> +    }
>>>> +
>>>> +  if (!__realpath (realname, absolutename))
>>>> +    {
>>>> +      free (absolutename);
>>>> +      errstring = N_("cannot find absolute path of shared object");
>>>> +      goto call_lose_errno;
>>>> +    }
>>>> +
>>>> +  free (realname);
>>>> +  realname = absolutename;
>>>>
>>>>    /* Look again to see if the real name matched another already loaded.  */
>>>>    for (l = GL(dl_ns)[nsid]._ns_loaded; l; l = l->l_next)
>>>> diff --git a/elf/dl-object.c b/elf/dl-object.c
>>>> index afd80a6..d93935b 100644
>>>> --- a/elf/dl-object.c
>>>> +++ b/elf/dl-object.c
>>>> @@ -158,55 +158,15 @@ _dl_new_object (char *realname, const char *libname, int type,
>>>>        char *origin;
>>>>        char *cp;
>>>>
>>>> -      if (realname[0] == '/')
>>>> +      /* It is an absolute path, calculated by realpath. Use it.
>>>> +       * But we have to make a copy since we strip out the trailing slash. */
>>>> +      assert (realname[0] == '/');
>>>> +      cp = origin = (char *) malloc (realname_len);
>>>> +      if (origin == NULL)
>>>>         {
>>>> -         /* It is an absolute path.  Use it.  But we have to make a
>>>> -            copy since we strip out the trailing slash.  */
>>>> -         cp = origin = (char *) malloc (realname_len);
>>>> -         if (origin == NULL)
>>>> -           {
>>>> -             origin = (char *) -1;
>>>> -             goto out;
>>>> -           }
>>>> +         origin = (char *) -1;
>>>> +         goto out;
>>>>         }
>>>> -      else
>>>> -       {
>>>> -         size_t len = realname_len;
>>>> -         char *result = NULL;
>>>> -
>>>> -         /* Get the current directory name.  */
>>>> -         origin = NULL;
>>>> -         do
>>>> -           {
>>>> -             char *new_origin;
>>>> -
>>>> -             len += 128;
>>>> -             new_origin = (char *) realloc (origin, len);
>>>> -             if (new_origin == NULL)
>>>> -               /* We exit the loop.  Note that result == NULL.  */
>>>> -               break;
>>>> -             origin = new_origin;
>>>> -           }
>>>> -         while ((result = __getcwd (origin, len - realname_len)) == NULL
>>>> -                && errno == ERANGE);
>>>> -
>>>> -         if (result == NULL)
>>>> -           {
>>>> -             /* We were not able to determine the current directory.
>>>> -                Note that free(origin) is OK if origin == NULL.  */
>>>> -             free (origin);
>>>> -             origin = (char *) -1;
>>>> -             goto out;
>>>> -           }
>>>> -
>>>> -         /* Find the end of the path and see whether we have to add a
>>>> -            slash.  We could use rawmemchr but this need not be
>>>> -            fast.  */
>>>> -         cp = (strchr) (origin, '\0');
>>>> -         if (cp[-1] != '/')
>>>> -           *cp++ = '/';
>>>> -       }
>>>> -
>>>>        /* Add the real file name.  */
>>>>        cp = __mempcpy (cp, realname, realname_len);
>>>>
>>>> diff --git a/elf/dl-realpath.c b/elf/dl-realpath.c
>>>> new file mode 100644
>>>> index 0000000..2549bb3
>>>> --- /dev/null
>>>> +++ b/elf/dl-realpath.c
>>>> @@ -0,0 +1,85 @@
>>>> +/* Dynamic loader version of realpath.
>>>> +   Copyright (C) 2014 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
>>>> +   <http://www.gnu.org/licenses/>.  */
>>>> +
>>>> +#include <stdlib.h>
>>>> +#include <unistd.h>
>>>> +#include <limits.h>
>>>> +#include <ldsodefs.h>
>>>> +
>>>> +/* Simplified implementation of realpath(): no dynamic memory use, no lstat(),
>>>> +   no set_errno(), no valid "rpath" on error, etc.  This simplifies cases
>>>> +   involving relative paths, specifically where $ORIGIN needs to be
>>>> +   calculated. For this relatively rare case, one could also imagine using
>>>> +   link_map.l_origin to avoid the getcwd() here, but the simpler code
>>>> +   here seems like a better solution.  */
>>>> +char * internal_function
>>>> +__realpath (const char *name, char *rpath)
>>>> +{
>>>> +  char *dest;
>>>> +  const char *start, *end;
>>>> +
>>>> +  if (name[0] != '/')
>>>> +    {
>>>> +      if (!__getcwd (rpath, PATH_MAX))
>>>> +       return NULL;
>>>> +      dest = __rawmemchr (rpath, '\0');
>>>> +    }
>>>> +  else
>>>> +    {
>>>> +      rpath[0] = '/';
>>>> +      dest = rpath + 1;
>>>> +    }
>>>> +
>>>> +  for (start = end = name; *start; start = end)
>>>> +    {
>>>> +      /* Skip sequence of multiple path-separators.  */
>>>> +      while (*start == '/')
>>>> +       ++start;
>>>> +
>>>> +      /* Find end of path component.  */
>>>> +      for (end = start; *end && *end != '/'; ++end)
>>>> +       /* Nothing.  */;
>>>> +
>>>> +      if (end - start == 0)
>>>> +       break;
>>>> +      else if (end - start == 1 && start[0] == '.')
>>>> +       /* nothing */;
>>>> +      else if (end - start == 2 && start[0] == '.' && start[1] == '.')
>>>> +       {
>>>> +         /* Back up to previous component, ignore if at root already.  */
>>>> +         if (dest > rpath + 1)
>>>> +           while ((--dest)[-1] != '/');
>>>> +       }
>>>> +      else
>>>> +       {
>>>> +         if (dest[-1] != '/')
>>>> +           *dest++ = '/';
>>>> +
>>>> +         if (dest + (end - start) >= rpath + PATH_MAX)
>>>> +           return NULL;
>>>> +
>>>> +         dest = __mempcpy (dest, start, end - start);
>>>> +         *dest = '\0';
>>>> +       }
>>>> +    }
>>>> +  if (dest > rpath + 1 && dest[-1] == '/')
>>>> +    --dest;
>>>> +  *dest = '\0';
>>>> +
>>>> +  return rpath;
>>>> +}
>>>> diff --git a/sysdeps/tile/dl-runtime.c b/sysdeps/tile/dl-runtime.c
>>>> index bcc00bc..45251d0 100644
>>>> --- a/sysdeps/tile/dl-runtime.c
>>>> +++ b/sysdeps/tile/dl-runtime.c
>>>> @@ -29,70 +29,6 @@
>>>>  #include <arch/sim.h>
>>>>  #include <dl-unmap-segments.h>
>>>>
>>>> -/* Like realpath(), but simplified: no dynamic memory use, no lstat(),
>>>> -   no set_errno(), no valid "rpath" on error, etc.  This handles some
>>>> -   simple cases where the simulator might not have a valid entry for
>>>> -   a loaded Elf object, in particular dlopen() with a relative path.
>>>> -   For this relatively rare case, one could also imagine using
>>>> -   link_map.l_origin to avoid the getcwd() here, but the simpler code
>>>> -   here seems like a better solution.  */
>>>> -static char *
>>>> -dl_realpath (const char *name, char *rpath)
>>>> -{
>>>> -  char *dest;
>>>> -  const char *start, *end;
>>>> -
>>>> -  if (name[0] != '/')
>>>> -    {
>>>> -      if (!__getcwd (rpath, PATH_MAX))
>>>> -        return NULL;
>>>> -      dest = __rawmemchr (rpath, '\0');
>>>> -    }
>>>> -  else
>>>> -    {
>>>> -      rpath[0] = '/';
>>>> -      dest = rpath + 1;
>>>> -    }
>>>> -
>>>> -  for (start = end = name; *start; start = end)
>>>> -    {
>>>> -      /* Skip sequence of multiple path-separators.  */
>>>> -      while (*start == '/')
>>>> -       ++start;
>>>> -
>>>> -      /* Find end of path component.  */
>>>> -      for (end = start; *end && *end != '/'; ++end)
>>>> -       /* Nothing.  */;
>>>> -
>>>> -      if (end - start == 0)
>>>> -       break;
>>>> -      else if (end - start == 1 && start[0] == '.')
>>>> -       /* nothing */;
>>>> -      else if (end - start == 2 && start[0] == '.' && start[1] == '.')
>>>> -       {
>>>> -         /* Back up to previous component, ignore if at root already.  */
>>>> -         if (dest > rpath + 1)
>>>> -           while ((--dest)[-1] != '/');
>>>> -       }
>>>> -      else
>>>> -       {
>>>> -         if (dest[-1] != '/')
>>>> -           *dest++ = '/';
>>>> -
>>>> -         if (dest + (end - start) >= rpath + PATH_MAX)
>>>> -            return NULL;
>>>> -
>>>> -         dest = __mempcpy (dest, start, end - start);
>>>> -         *dest = '\0';
>>>> -       }
>>>> -    }
>>>> -  if (dest > rpath + 1 && dest[-1] == '/')
>>>> -    --dest;
>>>> -  *dest = '\0';
>>>> -
>>>> -  return rpath;
>>>> -}
>>>> -
>>>>  /* Support notifying the simulator about new objects.  */
>>>>  void internal_function
>>>>  _dl_after_load (struct link_map *l)
>>>> @@ -117,7 +53,7 @@ _dl_after_load (struct link_map *l)
>>>>    DLPUTC (':');
>>>>
>>>>    /* Write the library path, including the terminating '\0'.  */
>>>> -  path = dl_realpath (l->l_name, pathbuf) ?: l->l_name;
>>>> +  path = __realpath (l->l_name, pathbuf) ?: l->l_name;
>>>>    for (size_t i = 0;; i++)
>>>>      {
>>>>        DLPUTC (path[i]);
>>>> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
>>>> index 9ad6d22..4525429 100644
>>>> --- a/sysdeps/unix/sysv/linux/Makefile
>>>> +++ b/sysdeps/unix/sysv/linux/Makefile
>>>> @@ -176,7 +176,7 @@ endif
>>>>
>>>>  ifeq ($(subdir),elf)
>>>>  sysdep-rtld-routines += dl-brk dl-sbrk dl-getcwd dl-openat64 dl-opendir \
>>>> -                       dl-fxstatat64
>>>> +                       dl-fxstatat64 dl-lxstat64
>>>>
>>>>  CPPFLAGS-lddlibc4 += -DNOT_IN_libc
>>>>
>>>> diff --git a/sysdeps/unix/sysv/linux/dl-lxstat64.c b/sysdeps/unix/sysv/linux/dl-lxstat64.c
>>>> new file mode 100644
>>>> index 0000000..63e6800
>>>> --- /dev/null
>>>> +++ b/sysdeps/unix/sysv/linux/dl-lxstat64.c
>>>> @@ -0,0 +1 @@
>>>> +#include <lxstat64.c>
>>>> diff --git a/sysdeps/unix/sysv/linux/dl-realpath.c b/sysdeps/unix/sysv/linux/dl-realpath.c
>>>> new file mode 100644
>>>> index 0000000..91652dc
>>>> --- /dev/null
>>>> +++ b/sysdeps/unix/sysv/linux/dl-realpath.c
>>>> @@ -0,0 +1,121 @@
>>>> +/* Dynamic loader version of realpath for linux.
>>>> +   Copyright (C) 2014 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
>>>> +   <http://www.gnu.org/licenses/>.  */
>>>> +
>>>> +#include <stdlib.h>
>>>> +#include <unistd.h>
>>>> +#include <limits.h>
>>>> +#include <ldsodefs.h>
>>>> +#include <sys/stat.h>
>>>> +#include <kernel-features.h>
>>>> +#include <sysdep.h>
>>>> +
>>>> +/* Simplified version of realpath which extends elf/dl-realpath.c to use
>>>> + * linux syscalls for handling symlinks */
>>>> +char * internal_function
>>>> +__realpath (const char *name, char *rpath)
>>>> +{
>>>> +  char *dest;
>>>> +  char extra_buf[PATH_MAX];
>>>> +  const char *start, *end;
>>>> +  int num_links = 0;
>>>> +
>>>> +  if (name[0] != '/')
>>>> +    {
>>>> +      if (!__getcwd (rpath, PATH_MAX))
>>>> +       return NULL;
>>>> +      dest = __rawmemchr (rpath, '\0');
>>>> +    }
>>>> +  else
>>>> +    {
>>>> +      rpath[0] = '/';
>>>> +      dest = rpath + 1;
>>>> +    }
>>>> +
>>>> +  for (start = end = name; *start; start = end)
>>>> +    {
>>>> +      struct stat64 st;
>>>> +      int n;
>>>> +      /* Skip sequence of multiple path-separators.  */
>>>> +      while (*start == '/')
>>>> +       ++start;
>>>> +
>>>> +      /* Find end of path component.  */
>>>> +      for (end = start; *end && *end != '/'; ++end)
>>>> +       /* Nothing.  */;
>>>> +
>>>> +      if (end - start == 0)
>>>> +       break;
>>>> +      else if (end - start == 1 && start[0] == '.')
>>>> +       /* nothing */;
>>>> +      else if (end - start == 2 && start[0] == '.' && start[1] == '.')
>>>> +       {
>>>> +         /* Back up to previous component, ignore if at root already.  */
>>>> +         if (dest > rpath + 1)
>>>> +           while ((--dest)[-1] != '/');
>>>> +       }
>>>> +      else
>>>> +       {
>>>> +         if (dest[-1] != '/')
>>>> +           *dest++ = '/';
>>>> +
>>>> +         if (dest + (end - start) >= rpath + PATH_MAX)
>>>> +           return NULL;
>>>> +
>>>> +         dest = __mempcpy (dest, start, end - start);
>>>> +         *dest = '\0';
>>>> +         if (__lxstat64 (_STAT_VER, rpath, &st) < 0)
>>>> +           return NULL;
>>>> +
>>>> +         if (S_ISLNK (st.st_mode))
>>>> +           {
>>>> +             char buf[PATH_MAX];
>>>> +             size_t len;
>>>> +
>>>> +             INTERNAL_SYSCALL_DECL (err);
>>>> +
>>>> +             n = INTERNAL_SYSCALL (readlink, err, 3, rpath, buf,
>>>> +                                   PATH_MAX - 1);
>>>> +
>>>> +             if (n <= 0 || buf[0] == '[')
>>>> +               return NULL;
>>>> +             buf[n] = '\0';
>>>> +
>>>> +             len = strlen (end);
>>>> +             if ((long int) (n + len) >= PATH_MAX)
>>>> +               return NULL;
>>>> +
>>>> +             /* Careful here, end may be a pointer into extra_buf... */
>>>> +             memmove (&extra_buf[n], end, len + 1);
>>>> +             name = end = memcpy (extra_buf, buf, n);
>>>> +
>>>> +             if (buf[0] == '/')
>>>> +               dest = rpath + 1;     /* Absolute symlink */
>>>> +             else
>>>> +               /* Back up to previous component, ignore if at root already: */
>>>> +               if (dest > rpath + 1)
>>>> +                 while ((--dest)[-1] != '/');
>>>> +           }
>>>> +       }
>>>> +    }
>>>> +  if (dest > rpath + 1 && dest[-1] == '/')
>>>> +    --dest;
>>>> +  *dest = '\0';
>>>> +
>>>> +  return rpath;
>>>> +
>>>> +}
>>>> --
>>>> 2.0.4
>>>>
>>>
>>> ping.