Added: Re-add system_linker_exec support initially added in 2fe4775 and removed in 1fac107 and libtermux-exec-linker-ld-preload.so $LD_PRELOAD library variant

- `lib/termux-exec_nos_c_tre/src/termux/api/termux_exec/ld_preload/direct/exec/ExecIntercept.c` from `libtermux-exec_nos_c_tre` handles the `system_linker_exec` now and uses `lib/termux-exec_nos_c_tre/src/termux/api/termux_exec/ld_preload/TermuxExecLDPreload.c` to get whether `system_linker_exec` should be used based on the `isSystemLinkerExecEnabled()` and `shouldEnableSystemLinkerExecForFile()` functions.
- The `libtermux-exec-linker-ld-preload.so` `$LD_PRELOAD` library variant has been added and is meant to intercept additional functions to solve other issues specific to `system_linker_exec` execution. The `libtermux-exec-direct-ld-preload.so` variant needs to support `system_linker_exec` as well as during package updates, before the `linker` variant is set as primary variant, the `direct` variant will get used for certain commands as it gets installed as the primary variant by default, and commands will fail if `system_linker_exec` is required to bypass execution restrictions. The primary `$LD_PRELOAD` library variant to be used is set by copying it to `$TERMUX__PREFIX/usr/lib/libtermux-exec-ld-preload.so` and this path is exported in `$LD_PRELOAD` by `login` script. This is done by the `postinst` script run during package installation, which runs `termux-exec-ld-preload-lib setup` to set the correct variant as per the execution type required for the Termux environment of the host device by running `termux-exec-system-linker-exec is-enabled` to check if `system_linker_exec` is to be enabled.
- Added the `string` `TERMUX_EXEC__SYSTEM_LINKER_EXEC__MODE` environment variable for whether to use `system_linker_exec` if `TERMUX_EXEC__EXECVE_CALL__INTERCEPT` is enabled. If set to `disable`, `system_linker_exec` will be disabled. If set to `enable`, then `system_linker_exec` will be enabled but only if required. If set to `force`, then `system_linker_exec` will be force enabled even if not required and is supported. The default value is `enable`. Check `shouldEnableSystemLinkerExecForFile()` in `ExecIntercept.h` and `ExecIntercept.c` for more info and how its handled. Docs will be added in a later commit. The `system_linker_exec` will now engage for executable or interpreter paths that are under `TERMUX_APP__DATA_DIR` or `TERMUX_APP__LEGACY_DATA_DIR` instead of `TERMUX__ROOTFS` (`TERMUX_BASE_DIR`).
- Use `android_buildVersionSdk_get()` from `libtermux-core_nos_c_tre` library to read `ANDROID__BUILD_VERSION_SDK` environment variable exported by Termux app to get Android build version sdk, and if its not set, then from the `android_get_device_api_level()` call provided by `<android/api-level.h>`, which gets it from the system properties, which should be slower.
- Fix the environment `envp` being copied twice during `execve` for system bin paths, once for unsetting `LD_` variables and then to set `TERMUX_EXEC__PROC_SELF_EXE`. The `modifyExecEnv()` function now handles all changes to environment with a single copy.
- Fix `TERMUX_EXEC__PROC_SELF_EXE` being set even if `system_linker_exec` is not being used on `targetSdkVersion <= 28`, etc, and also not being unset when going from `system_linker_exec` to direct execution like system binaries. Packages will be patched to detect if `system_linker_exec` is being used to modify their behaviour, which shouldn't be modified for direct execution.

Author: agnostic-apollo

Makefile

@@ -63,6 +63,7 @@ export override BUILD_OUTPUT_DIR := $(BUILD_DIR)/output# Default value: `build/o
 export override TMP_BUILD_OUTPUT_DIR := $(BUILD_OUTPUT_DIR)/tmp# Default value: `build/output/tmp`
 
 export override PREFIX_BUILD_OUTPUT_DIR := $(BUILD_OUTPUT_DIR)/usr# Default value: `build/output/usr`
+export override BIN_BUILD_OUTPUT_DIR := $(PREFIX_BUILD_OUTPUT_DIR)/bin# Default value: `build/output/usr/bin`
 export override LIB_BUILD_OUTPUT_DIR := $(PREFIX_BUILD_OUTPUT_DIR)/lib# Default value: `build/output/usr/lib`
 export override LIBEXEC_BUILD_OUTPUT_DIR := $(PREFIX_BUILD_OUTPUT_DIR)/libexec# Default value: `build/output/usr/libexec`
 export override TESTS_BUILD_OUTPUT_DIR := $(LIBEXEC_BUILD_OUTPUT_DIR)/installed-tests/termux-exec# Default value: `build/output/usr/libexec/installed-tests/termux-exec`
@@ -236,7 +237,7 @@ CLANG_TIDY ?= clang-tidy
 # - https://www.gnu.org/software/make/manual/html_node/Parallel-Disable.html
 .NOTPARALLEL:
 
-all: | pre-build build-libtermux-exec_nos_c_tre build-libtermux-exec-direct-ld-preload build-termux-exec-main-app
+all: | pre-build build-libtermux-exec_nos_c_tre build-libtermux-exec-direct-ld-preload build-libtermux-exec-linker-ld-preload build-termux-exec-main-app
 	@printf "\ntermux-exec-package: %s\n" "Building packaging/debian/*"
 	@mkdir -p $(DEBIAN_PACKAGING_BUILD_OUTPUT_DIR)
 	find packaging/debian -mindepth 1 -maxdepth 1 -type f -name "*.in" -exec sh -c \
@@ -258,6 +259,15 @@ pre-build: | clean
 
 build-termux-exec-main-app:
 	@printf "\ntermux-exec-package: %s\n" "Building app/main"
+	@mkdir -p $(BIN_BUILD_OUTPUT_DIR)
+
+
+	@printf "\ntermux-exec-package: %s\n" "Building app/main/scripts/*"
+	find app/main/scripts -type f -name "*.in" -exec sh -c \
+		'sed $(TERMUX__CONSTANTS__SED_ARGS) "$$1" > $(BIN_BUILD_OUTPUT_DIR)/"$$(basename "$$1" | sed "s/\.in$$//")"' sh "{}" \;
+	find $(BIN_BUILD_OUTPUT_DIR) -maxdepth 1 -exec chmod 700 "{}" \;
+	find app/main/scripts -type l -exec cp -a "{}" $(BIN_BUILD_OUTPUT_DIR)/ \;
+
 
 build-libtermux-exec_nos_c_tre:
 	@printf "\ntermux-exec-package: %s\n" "Building lib/termux-exec_nos_c_tre"
@@ -307,6 +317,10 @@ build-libtermux-exec-direct-ld-preload:
 	@# primary library variant exported in `$LD_PRELOAD` by copying it
 	@# to `libtermux-exec-ld-preload.so`.
 	@# Creating a symlink may have performance impacts.
+	@# The `postinst` script run during package installation runs
+	@# `termux-exec-ld-preload-lib setup` to set the correct variant
+	@# as per the execution type required for the Termux environment
+	@# of the host device by running.
 	cp -a $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec-direct-ld-preload.so $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec-ld-preload.so
 
 	@# For backward compatibility, symlink `libtermux-exec.so` to
@@ -317,18 +331,39 @@ build-libtermux-exec-direct-ld-preload:
 	rm -f $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec.so
 	ln -s libtermux-exec-ld-preload.so $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec.so
 
+build-libtermux-exec-linker-ld-preload:
+	@mkdir -p $(LIB_BUILD_OUTPUT_DIR)
+
+	@# Unlike `libtermux-exec_nos_c_tre.so` and `libtermux-exec_nos_c_tre.a`, all
+	@# symbols are hidden, except the exported functions with
+	@# `default` visibility with `__attribute__((visibility("default")))`,
+	@# defined in the `TermuxExecLinkerLDPreloadEntryPoint.c` file meant to
+	@# be intercepted by `$LD_PRELOAD`.
+	@# `nm --demangle --dynamic --defined-only --extern-only /home/builder/.termux-build/termux-exec/src/build/output/usr/lib/libtermux-exec-linker-ld-preload.so`
+	@printf "\ntermux-exec-package: %s\n" "Building lib/libtermux-exec-linker-ld-preload"
+	$(CC) $(CFLAGS) $(LIBTERMUX_EXEC__NOS__C__CPPFLAGS) \
+		-L$(LIB_BUILD_OUTPUT_DIR) $(LDFLAGS) -Wl,--exclude-libs=ALL \
+		$(TERMUX__CONSTANTS__MACRO_FLAGS) \
+		-fPIC -shared -fvisibility=hidden \
+		-o $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec-linker-ld-preload.so \
+		app/termux-exec-linker-ld-preload/src/termux/api/termux_exec/ld_preload/linker/TermuxExecLinkerLDPreloadEntryPoint.c \
+		-l:libtermux-exec_nos_c_tre.a -l:libtermux-core_nos_c_tre.a
+
 
 
 clean:
 	rm -rf $(BUILD_OUTPUT_DIR)
 
 install:
 	@printf "termux-exec-package: %s\n" "Installing termux-exec-package in $(TERMUX_EXEC_PKG__INSTALL_PREFIX)"
+	install -d $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/bin
 	install -d $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/include
 	install -d $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib
 	install -d $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/libexec
 
 
+	find $(BIN_BUILD_OUTPUT_DIR) -maxdepth 1 \( -type f -o -type l \) -exec cp -a "{}" $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/bin/ \;
+
 	rm -rf $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/include/termux-exec
 	install -d $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/include/termux-exec/termux
 
@@ -338,6 +373,7 @@ install:
 
 	install $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec-ld-preload.so $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec-ld-preload.so
 	install $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec-direct-ld-preload.so $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec-direct-ld-preload.so
+	install $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec-linker-ld-preload.so $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec-linker-ld-preload.so
 	@# Use `cp` for symlink as `install` will copy the target regular file instead.
 	cp -a $(LIB_BUILD_OUTPUT_DIR)/libtermux-exec.so $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec.so
 
@@ -350,6 +386,9 @@ install:
 uninstall:
 	@printf "termux-exec-package: %s\n" "Uninstalling termux-exec-package from $(TERMUX_EXEC_PKG__INSTALL_PREFIX)"
 
+	find app/main/scripts \( -type f -o -type l \) -exec sh -c \
+		'rm -f $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/bin/"$$(basename "$$1" | sed "s/\.in$$//")"' sh "{}" \;
+
 	rm -rf $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/include/termux-exec
 
 
@@ -358,6 +397,7 @@ uninstall:
 
 	rm -f $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec-ld-preload.so
 	rm -f $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec-direct-ld-preload.so
+	rm -f $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec-linker-ld-preload.so
 	rm -f $(TERMUX_EXEC_PKG__INSTALL_PREFIX)/lib/libtermux-exec.so
 
 	@printf "\ntermux-exec-package: %s\n\n" "Uninstall termux-exec-package successful"
@@ -382,4 +422,4 @@ check:
 
 
 
-.PHONY: all pre-build build-termux-exec-main-app build-libtermux-exec_nos_c_tre build-libtermux-exec-direct-ld-preload clean install uninstall packaging-debian-build format check
+.PHONY: all pre-build build-termux-exec-main-app build-libtermux-exec_nos_c_tre build-libtermux-exec-direct-ld-preload build-libtermux-exec-linker-ld-preload clean install uninstall packaging-debian-build format check

app/main/scripts/termux/api/termux_exec/ld_preload/termux-exec-ld-preload-lib.in

@@ -0,0 +1,203 @@
+#!@TERMUX__PREFIX@/bin/sh
+# shellcheck shell=sh
+# shellcheck disable=SC2039,SC2059,SC3043
+
+termux_exec__ld_preload_lib__init() {
+
+TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL___N="@TERMUX_ENV__S_TERMUX_EXEC@LD_PRELOAD_LIB__LOG_LEVEL"
+termux_exec__ld_preload_lib__copy_variable TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL "$TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL___N" || return $?
+case "${TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL:-}" in
+    0|1|2) :;; *) TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL=1;; # Default: `1` (OFF=0, NORMAL=1, DEBUG=2)
+esac
+
+TERMUX_EXEC__SYSTEM_LINKER_EXEC__LOG_LEVEL___N="@TERMUX_ENV__S_TERMUX_EXEC@SYSTEM_LINKER_EXEC__LOG_LEVEL"
+
+TERMUX__PREFIX___N="@TERMUX_ENV__S_TERMUX@PREFIX"
+termux_exec__ld_preload_lib__copy_variable TERMUX__PREFIX "$TERMUX__PREFIX___N" || return $?
+case "${TERMUX__PREFIX:-}" in
+    /*[!/]) :;; *) TERMUX__PREFIX="@TERMUX__PREFIX@";;
+esac
+
+}
+
+
+
+termux_exec__ld_preload_lib__log() { local log_level="${1}"; shift; if [ "$TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL" -ge "$log_level" ]; then echo "@TERMUX__LNAME@-exec:" "$@"; fi }
+termux_exec__ld_preload_lib__log_error() { echo "@TERMUX__LNAME@-exec:" "$@" 1>&2; }
+termux_exec__ld_preload_lib__log_error_for_level() { local log_level="${1}"; shift; if [ "$TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL" -ge "$log_level" ]; then echo "@TERMUX__LNAME@-exec:" "$@" 1>&2; fi }
+
+
+
+##
+# `termux_exec__ld_preload_lib__main` [`<argument...>`]
+##
+termux_exec__ld_preload_lib__main() {
+
+    termux_exec__ld_preload_lib__init || return $?
+
+
+    if [ "${1:-}" = "-h" ] || [ "${1:-}" = "--help" ]; then
+        termux_exec__ld_preload_lib__show_help || return $?
+        return 0
+    elif [ "${1:-}" = "--version" ]; then
+        echo "@TERMUX_EXEC_PKG__VERSION@" || return $?
+        return 0
+    fi
+
+
+    local command_type="${1:-}"
+    [ $# -gt 0 ] && shift 1
+
+    if [ "$command_type" = "setup" ]; then
+        if [ "${1:-}" = "-q" ] || [ "${1:-}" = "--quiet" ]; then
+            TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL=0
+            shift 1
+        elif [ "${1:-}" = "-v" ]; then
+            TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL=2
+            shift 1
+        fi
+    else
+        echo "The command '$command_type' passed to 'termux-exec-ld-preload-lib' is not valid." 1>&2
+        return 64 # EX__USAGE
+    fi
+
+
+    termux_exec__ld_preload_lib__set_variable "$TERMUX_EXEC__SYSTEM_LINKER_EXEC__LOG_LEVEL___N" "$TERMUX_EXEC__LD_PRELOAD_LIB__LOG_LEVEL" || return $?
+    export "${TERMUX_EXEC__SYSTEM_LINKER_EXEC__LOG_LEVEL___N?}" || return $?
+
+
+    if [ "$command_type" = "setup" ]; then
+        termux_exec__ld_preload_lib__setup__run_command setup || return $?
+    fi
+
+    return 0
+
+}
+
+
+
+##
+# `termux_exec__ld_preload_lib__setup__run_command`
+##
+termux_exec__ld_preload_lib__setup__run_command() {
+
+    local system_linker_exec_enabled
+
+    system_linker_exec_enabled="$(termux-exec-system-linker-exec is-enabled)" || return $?
+
+    local ld_preload_file
+
+    if [ "$system_linker_exec_enabled" != "true" ]; then
+        ld_preload_file="$TERMUX__PREFIX/lib/libtermux-exec-direct-ld-preload.so"
+    else
+        ld_preload_file="$TERMUX__PREFIX/lib/libtermux-exec-linker-ld-preload.so"
+    fi
+    termux_exec__ld_preload_lib__log 1 "Setting primary Termux '\$LD_PRELOAD' library in 'libtermux-exec-ld-preload.so' to '$ld_preload_file'"
+
+    mkdir -p "$TERMUX__PREFIX/lib" || return $?
+
+    # Prevent `Segmentation fault (SIGSEGV fault addr)` when running
+    # commands in calling shell of the script after new file has been
+    # copied below.
+    rm -f "$TERMUX__PREFIX/lib/libtermux-exec-ld-preload.so" || return $?
+
+    # Prevent `CANNOT LINK EXECUTABLE "cp": library "/data/data/com.termux/files/usr/lib/libtermux-exec-ld-preload.so" not found: needed by main executable`
+    unset LD_PRELOAD || return $?
+
+    cp -a "$ld_preload_file" "$TERMUX__PREFIX/lib/libtermux-exec-ld-preload.so" || return $?
+
+}
+
+
+
+##
+# `termux_exec__ld_preload_lib__is_valid_shell_name` `<name>`
+##
+termux_exec__ld_preload_lib__is_valid_shell_name() {
+
+    if [ -z "${1:-}" ]; then
+        return 1
+    fi
+
+    local name_rest="${1#?}" # 1:end
+    local name_first_char="${1%"$name_rest"}" # 0:1
+    case "$name_first_char" in
+        [a-zA-Z_])
+            case "$name_rest" in
+                *[!a-zA-Z0-9_]*) return 1;;
+                *) return 0;;
+            esac;;
+        *) return 1;;
+    esac
+
+}
+
+##
+# `termux_exec__ld_preload_lib__set_variable` `<variable_name>` `<variable_value>`
+##
+termux_exec__ld_preload_lib__set_variable() {
+
+    local variable_name="${1:-}"
+    local variable_value="${2:-}"
+
+    if ! termux_exec__ld_preload_lib__is_valid_shell_name "$variable_name"; then
+        termux_exec__ld_preload_lib__log_error "The variable_name '$variable_name' is not a valid shell variable name."
+        return 64 # EX__USAGE
+    fi
+
+    eval "$variable_name"=\"\$variable_value\"
+
+}
+
+termux_exec__ld_preload_lib__copy_variable() {
+
+    local output_variable_name="${1:-}"
+    local input_variable_name="${2:-}"
+
+    if ! termux_exec__ld_preload_lib__is_valid_shell_name "$output_variable_name"; then
+        termux_exec__ld_preload_lib__log_error "The output_variable_name '$output_variable_name' is not a valid shell variable name."
+        return 1
+    fi
+
+    if ! termux_exec__ld_preload_lib__is_valid_shell_name "$input_variable_name"; then
+        termux_exec__ld_preload_lib__log_error "The input_variable_name '$input_variable_name' is not a valid shell variable name."
+        return 1
+    fi
+
+    eval "$output_variable_name"=\"\$\{"$input_variable_name":-\}\"
+
+}
+
+
+
+##
+# `termux_exec__ld_preload_lib__show_help`
+##
+termux_exec__ld_preload_lib__show_help() {
+
+    cat <<'HELP_EOF'
+termux-exec-ld-preload-lib can be used to manage Termux '$LD_PRELOAD'
+library.
+
+
+Usage:
+    termux-exec-ld-preload-lib [command_options] <command>
+
+Available commands:
+    setup                     Setup the primary Termux '$LD_PRELOAD'
+                              library in 'libtermux-exec-ld-preload.so'
+                              to direct or linker variant.
+
+Available command_options:
+    [ -h | --help ]           Display this help screen.
+    [ --version ]             Display version.
+    [ -q | --quiet ]          Set log level to 'OFF'.
+    [ -v ]
+                              Set log level to 'DEBUG'.
+HELP_EOF
+
+}
+
+
+
+termux_exec__ld_preload_lib__main "$@"