elf: Handle non-directory name in search path (BZ 31035)

The open_path stops if a relative path in search path contains a
component that is a non directory (for instance, if the component
is an existing file).

For instance:

  $ cat > lib.c <<EOF
  > void foo (void) {}
  > EOF
  $ gcc -shared -fPIC -o lib.so lib.c
  $ cat > main.c <<EOF
  extern void foo ();
  int main () { foo (); return 0; }
  EOF
  $ gcc -o main main.c lib.so
  $ LD_LIBRARY_PATH=. ./main
  $ LD_LIBRARY_PATH=non-existing/path:. ./main
  $ LD_LIBRARY_PATH=$(pwd)/main:. ./main
  $ LD_LIBRARY_PATH=./main:. ./main
  ./main: error while loading shared libraries: lib.so: cannot open shared object file: No such file or directory

The invalid './main' should be ignored as a non-existent one,
instead as a valid but non accessible file.

Absolute paths do not trigger this issue because their status are
initialized as 'unknown' and open_path check if this is a directory.

Checked on x86_64-linux-gnu.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

elf/tst-non-directory-path.sh

@@ -0,0 +1,77 @@
+#!/bin/sh
+# Test if library search path does not terminates with non-directory
+# components.
+# Copyright (C) 2023 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
+
+rtld=$1
+test_program=$2
+test_wrapper_env=$3
+run_program_env=$4
+# Remove the last space to allow concatenate extra paths.
+library_path=$(echo $5)
+objpfx=$6
+
+test_binary=$(basename ${test_program})
+test_libpath=${test_binary}-x
+
+mkdir -p ${objpfx}/${test_libpath}
+mv ${objpfx}/tst-non-directory-mod.so ${objpfx}/${test_libpath}
+
+# Check with absolute paths.
+${test_wrapper_env} \
+${run_program_env} \
+$rtld --inhibit-cache \
+  --library-path \
+  "$library_path":"${objpfx}"tst-non-directory-invalid:"${objpfx}"${test_libpath} \
+  $test_program 2>&1 && rc=0 || rc=$?
+
+${test_wrapper_env} \
+${run_program_env} \
+$rtld --inhibit-cache \
+  --library-path \
+  "$library_path":"${objpfx}"${test_binary}:"${objpfx}"${test_libpath} \
+  $test_program 2>&1 && rc=0 || rc=$?
+
+# Relative paths along with non-existent path in search list.
+cd "$objpfx"
+${test_wrapper_env} \
+${run_program_env} \
+$rtld --inhibit-cache \
+  --library-path \
+  "$library_path":../elf/tst-non-directory-invalid::../elf/${test_libpath} \
+  $test_program 2>&1 && rc=0 || rc=$?
+
+# Relative paths along with component in the path is not a directory in search list.
+${test_wrapper_env} \
+${run_program_env} \
+$rtld --inhibit-cache \
+  --library-path \
+  "$library_path":../elf/${test_binary}:../elf/${test_libpath} \
+  $test_program 2>&1 && rc=0 || rc=$?
+
+# Relative paths along with non-existent path and a component in the path that is not a directory.
+${test_wrapper_env} \
+${run_program_env} \
+$rtld --inhibit-cache \
+  --library-path \
+  "$library_path":../elf/tst-non-directory-invalid:../elf/${test_binary}:../elf/${test_libpath} \
+  $test_program 2>&1 && rc=0 || rc=$?
+
+exit $rc