elf: Canonicalize $ORIGIN in an explicit ld.so invocation [BZ 25263]

When an executable is invoked directly, we calculate $ORIGIN by calling
readlink on /proc/self/exe, which the Linux kernel resolves to the
target of any symlinks.  However, if an executable is run through ld.so,
we cannot use /proc/self/exe and instead use the path given as an
argument. This leads to a different calculation of $ORIGIN, which is
most notable in that it causes ldd to behave differently (e.g., by not
finding a library) from directly running the program.

To make the behavior consistent, take advantage of the fact that the
kernel also resolves /proc/self/fd/ symlinks to the target of any
symlinks in the same manner, so once we have opened the main executable
in order to load it, replace the user-provided path with the result of
calling readlink("/proc/self/fd/N").

(On non-Linux platforms this resolution does not happen and so no
behavior change is needed.)

Co-authored-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Geoffrey Thomas 2025-02-18 15:58:16 -05:00 committed by Adhemerval Zanella
parent 9e51ae3cd0
commit 372c632ce7
9 changed files with 149 additions and 0 deletions

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@ -455,6 +455,7 @@ tests += \
tst-noload \
tst-non-directory-path \
tst-null-argv \
tst-origin \
tst-p_align1 \
tst-p_align2 \
tst-p_align3 \
@ -761,6 +762,7 @@ modules-names += \
libmarkermod5-3 \
libmarkermod5-4 \
libmarkermod5-5 \
liborigin-mod \
libtracemod1-1 \
libtracemod2-1 \
libtracemod3-1 \
@ -3397,3 +3399,24 @@ $(objpfx)tst-nolink-libc-2: $(objpfx)tst-nolink-libc.o
-Wl,--dynamic-linker=$(objpfx)ld.so
$(objpfx)tst-nolink-libc-2.out: $(objpfx)tst-nolink-libc-2 $(objpfx)ld.so
$< > $@ 2>&1; $(evaluate-test)
$(objpfx)tst-origin: $(objpfx)tst-origin.o $(objpfx)liborigin-mod.so
$(LINK.o) -o $@ -B$(csu-objpfx) $(LDFLAGS.so) $< \
-Wl,-rpath,\$$ORIGIN \
-L$(subst :, -L,$(rpath-link)) -Wl,--no-as-needed -lorigin-mod
$(objpfx)liborigin-mod.so: $(objpfx)liborigin-mod.os
$(LINK.o) -shared -o $@ -B$(csu-objpfx) $(LDFLAGS.so) \
$(LDFLAGS-soname-fname) \
$<
$(objpfx)tst-origin.out: tst-origin.sh $(objpfx)tst-origin
$(SHELL) \
$< \
'$(common-objpfx)' \
'$(test-wrapper-env)' \
'$(run-program-env)' \
'$(rpath-link)' \
tst-origin \
liborigin-mod.so \
> $@; \
$(evaluate-test)

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@ -965,6 +965,12 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
{
assert (nsid == LM_ID_BASE);
memset (&id, 0, sizeof (id));
char *realname_can = _dl_canonicalize (fd);
if (realname_can != NULL)
{
free (realname);
realname = realname_can;
}
}
else
{

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@ -47,3 +47,9 @@ _dl_get_origin (void)
return result;
}
char *
_dl_canonicalize (int fd)
{
return NULL;
}

1
elf/liborigin-mod.c Normal file
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@ -0,0 +1 @@
void foo (void) {}

26
elf/tst-origin.c Normal file
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@ -0,0 +1,26 @@
/* Test if $ORIGIN works correctly with symlinks (BZ#25263)
Copyright (C) 2025 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
<https://www.gnu.org/licenses/>. */
extern void foo (void);
int
main (int argc, char *argv[])
{
foo ();
return 0;
}

60
elf/tst-origin.sh Executable file
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@ -0,0 +1,60 @@
#!/bin/sh
# Test if $ORIGIN works correctly with symlinks (BZ 25263)
# Copyright (C) 2025 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
# <https://www.gnu.org/licenses/>.
set -e
objpfx=$1
test_wrapper_env=$2
run_program_env=$3
library_path=$4
test_program=$5
test_library=$6
cleanup()
{
# Move the binary and library back to build directory
mv $tmpdir/sub/$test_program ${objpfx}elf
mv $tmpdir/sub/$test_library ${objpfx}elf
rm -rf $tmpdir
}
tmpdir=$(mktemp -d "${objpfx}elf/tst-origin.XXXXXXXXXX")
#trap cleanup 0
mkdir ${tmpdir}/sub
# Remove the dependency from $library_path
mv ${objpfx}elf/$test_program $tmpdir/sub
mv ${objpfx}elf/$test_library $tmpdir/sub
cd ${tmpdir}
ln -s sub/$test_program $test_program
#${test_wrapper_env} \
#${run_program_env} \
#${objpfx}elf/ld.so --library-path "$library_path" \
# ./$test_program 2>&1 && rc=0 || rc=$?
# Also check if ldd resolves the dependency
LD_TRACE_LOADED_OBJECTS=1 \
${objpfx}elf/ld.so --library-path "$library_path" \
./$test_program 2>&1 | grep 'not found' && rc=1 || rc=0
exit $rc

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@ -1223,6 +1223,10 @@ extern struct link_map * _dl_get_dl_main_map (void) attribute_hidden;
/* Find origin of the executable. */
extern const char *_dl_get_origin (void) attribute_hidden;
/* Return the canonalized path name from the opened file descriptor FD,
or NULL otherwise. */
extern char * _dl_canonicalize (int fd) attribute_hidden;
/* Count DSTs. */
extern size_t _dl_dst_count (const char *name) attribute_hidden;

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@ -300,6 +300,8 @@ ifeq ($(subdir),elf)
check-execstack-xfail += ld.so libc.so libpthread.so
# We always create a thread for signals
test-xfail-tst-single_threaded-pthread-static = yes
# Bug 25263
test-xfail-tst-origin = yes
CFLAGS-tst-execstack.c += -DDEFAULT_RWX_STACK=1
endif

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@ -21,6 +21,7 @@
#include <fcntl.h>
#include <ldsodefs.h>
#include <sysdep.h>
#include <fd_to_filename.h>
/* On Linux >= 2.1 systems which have the dcache implementation we can get
the path of the application from the /proc/self/exe symlink. Try this
@ -72,3 +73,23 @@ _dl_get_origin (void)
return result;
}
/* On Linux, readlink on the magic symlinks in /proc/self/fd also has
the same behavior of returning the canonical path from the dcache.
If it does not work, we do not bother to canonicalize. */
char *
_dl_canonicalize (int fd)
{
struct fd_to_filename fdfilename;
char canonical[PATH_MAX];
char *path = __fd_to_filename (fd, &fdfilename);
int size = INTERNAL_SYSCALL_CALL (readlinkat, AT_FDCWD, path,
canonical, PATH_MAX - 1);
if (size >= 0)
{
canonical[size] = '\0';
return __strdup (canonical);
}
return NULL;
}