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

[Brennan Shacklett <bpshacklett at gmail dot com>]

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.