libcmdsdaskpass.so

cmdsdaskpass.c

#/* \
make -C "$(dirname "$0")" -f "$0" "$@"; exit $?
libcmdsdaskpass.so: LDFLAGS += -shared
libcmdsdaskpass.so: LDLIBS += -ldl
libcmdsdaskpass.so: cmdsdaskpass.o
	$(CC) $(LDFLAGS) $(TARGET_ARCH) $^ $(LOADLIBES) $(LDLIBS) -o $@
cmdsdaskpass.o: CFLAGS += -fPIC
cmdsdaskpass.o: cmdsdaskpass.c
	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c -o $@ $^
help:
	$(info )
	$(info LD_PRELOAD to replace $$(systemd-ask-password $$*) with the result of invocation)
	$(info in ARGV without being visible in /proc/$$/cmdline, building on code taken from)
	$(info http://serverfault.com/a/592941)
	$(info http://xrefactor.com/blog/polyglot-in-c-makefile-and-shell-script)
	$(info )
.PHONY: help
#*/
#define _GNU_SOURCE
#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sysexits.h>
#include <unistd.h>
	static int (*real_main)(int, char **, char **);
	static const char replace_arg_begin[] = "$(systemd-ask-password";
	static const char replace_arg_end[] = ")";
	static const char sd_askpass_cmd[] = "/usr/bin/systemd-ask-password";
	static const char whitespace[] = " \t\n";
	static int preload_main(int argc, char **argv, char **envp) {
	    int i, j, fds[2];
	    for (i = 1; i < argc; i++) {
	        int begin = strlen(replace_arg_begin);
	        int end = strlen(argv[i]) - strlen(replace_arg_end);
	        if (begin < end &&
	                memcmp(argv[i], replace_arg_begin, strlen(replace_arg_begin)) == 0 &&
	                memcmp(argv[i] + end, replace_arg_end, strlen(replace_arg_end)) == 0) {
	            pid_t child;
	            char *s, *args = malloc(end - begin + 1);
	            const char **arga = calloc((end - begin + 1) / 2 + 2, sizeof(char *));
	            memcpy(args, argv[i] + begin, end - begin);
	            args[end - begin] = '\0';
	            arga[0] = sd_askpass_cmd;
	            for (j = 1, s = args + strspn(args, whitespace); s[0]; s += strspn(s, whitespace)) {
	                arga[j++] = s;
	                if (s[0] == '-' && (s[1] != '-' || s[2] != '\0' && !strchr(whitespace, s[2]))) {
	                    s += strcspn(s, whitespace);
	                    if (s[0]) {
	                        *s++ = '\0';
	                    }
	                } else if (s[0] == '-' && s[1] == '-') {
	                    (s += 2)[0] = '\0';
	                    if (&s[1] < &args[end - begin]) {
	                        s += 1 + strspn(&s[1], whitespace);
	                    }
	                    if (s < &args[end - begin]) {
	                        arga[j++] = s;
	                        s = &args[end - begin];
	                    }
	                } else {
	                    break;
	                }
	            }
	            if (pipe2(fds, O_CLOEXEC) < 0) {
	                perror("pipe2");
	                exit(EX_OSERR);
	            }
	            if ((child = fork()) < 0) {
	                perror("fork");
	                exit(EX_OSERR);
	            } else if (child == 0) {
	                if (fds[0] != 1) {
	                    close(fds[0]);
	                }
	                if (fds[1] != 1) {
	                    dup2(fds[1], 1);
	                    close(fds[1]);
	                }
	                execvp(arga[0], (char **)arga);
	                perror("execv");
	                _exit(EX_UNAVAILABLE);
	            } else {
	                FILE *p;
	                size_t n = 0;
	                free(arga);
	                free(args);
	                close(fds[1]);
	                if (!(p = fdopen(fds[0], "r"))) {
	                    perror("child");
	                    exit(EX_NOINPUT);
	                }
	                args = NULL;
	                j = getline(&args, &n, p);
	                if (j < 0) {
	                    perror("getline");
	                    exit(EX_NOINPUT);
	                }
	                fclose(p);
	                close(fds[0]);
	                if (args[j - 1] == '\n') {
	                    args[j - 1] = '\0';
	                }
	                argv[i] = args;
	            }
	        }
	    }
	    return real_main(argc, argv, envp);
	}
	int __libc_start_main(
	        int (*main)(int, char **, char **),
	        int argc, char **ubp_av,
	        void (*init)(void),
	        void (*fini)(void),
	        void (*rtld_fini)(void),
	        void *stack_end) {
	    int (*next)(
	            int (*)(int, char **, char **),
	            int, char **,
	            void (*)(void),
	            void (*)(void),
	            void (*)(void),
	            void *) =
	        dlsym(RTLD_NEXT, __func__);
	    real_main = main;
	    return next(preload_main, argc, ubp_av, init, fini, rtld_fini, stack_end);
	}