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Re: [PATCH][BZ 17251] Calculate RPATH $ORIGIN from absolute path
- From: Brennan Shacklett <bpshacklett at gmail dot com>
- To: libc-alpha at sourceware dot org
- Date: Mon, 6 Oct 2014 09:18:37 -0700
- Subject: Re: [PATCH][BZ 17251] Calculate RPATH $ORIGIN from absolute path
- Authentication-results: sourceware.org; auth=none
- References: <1407860209-21797-1-git-send-email-bpshacklett at gmail dot com> <CAL8Wma9QBp9o7p2iipTUHDb38pNJxzopq8WHrgrU+pQTsqT1Ug at mail dot gmail dot com> <CAL8Wma-GKCeT=3qFdQC3Db_PVZZD2TpDbaxphko+PL7e2SYfSg at mail dot gmail dot com>
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.