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

[Brennan Shacklett <bpshacklett at gmail dot com>]

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.