Initial commit.

Author: geofft

.gitignore

@@ -0,0 +1 @@
+*.so

Makefile

@@ -0,0 +1,12 @@
+LIBS = -ldl
+CFLAGS =
+
+CFLAGS += -DDEBUG
+
+libenviable.so: enviable.c
+	$(CC) $(CFLAGS) -fPIC -shared -o $@ $< $(LIBS)
+
+clean:
+	rm -f libenviable.so
+
+.PHONY: clean

enviable.c

@@ -0,0 +1,149 @@
+/* enviable - An LD_PRELOAD to set environment variables at runtime.
+ * Usage: LD_PRELOAD=./libenviable.so bash
+ *
+ *
+ * Copyright (c) 2013  Geoffrey Thomas <[email protected]>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+*/
+
+#define _GNU_SOURCE
+#include <sys/inotify.h>
+#include <dlfcn.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#ifdef DEBUG
+#include <stdio.h>
+#define maybe_perror(s) perror(s)
+#else
+#define maybe_perror(s)
+#endif
+
+static int (*real___libc_current_sigrtmin)(void) = NULL;
+
+static char *watchfile = "/tmp/vars";
+
+int
+__libc_current_sigrtmin(void)
+{
+	return real___libc_current_sigrtmin() + 1;
+}
+
+static void
+enviable_callback(int signum, siginfo_t *si, void *context)
+{
+	struct inotify_event event;
+	if (read(si->si_fd, &event, sizeof(event)) != sizeof(event))
+		return;
+
+	FILE *fd = fopen(watchfile, "r");
+	if (!fd) {
+		return;
+	}
+	char *buf = NULL;
+	size_t n = 0;
+	ssize_t len;
+	while ((len = getline(&buf, &n, fd)) > 0) {
+		if (buf[len - 1] == '\n') {
+			buf[len - 1] = '\0';
+		} else {
+			/* Conservatively reject partial lines. */
+			continue;
+		}
+		char *eq = strchr(buf, '=');
+		*eq = '\0';
+		setenv(buf, eq + 1, 1);
+	}
+	free(buf);
+	fclose(fd);
+}
+
+void __attribute__((constructor))
+enviable_init(void)
+{
+	real___libc_current_sigrtmin = dlsym(RTLD_NEXT, "__libc_current_sigrtmin");
+	if (!real___libc_current_sigrtmin) {
+		/* Give up; we can't safely claim a signal. */
+		maybe_perror("enviable: incompatible libc");
+		return;
+	}
+
+	int fd = inotify_init1(IN_NONBLOCK | IN_CLOEXEC);
+	if (fd == -1) {
+		maybe_perror("enviable: inotify_init");
+		return;
+	}
+
+	int watch = inotify_add_watch(fd, watchfile, IN_CLOSE_WRITE);
+	if (watch == -1) {
+		maybe_perror("enviable: inotify_add_watch");
+		goto err;
+	}
+
+	int sigrtmin = real___libc_current_sigrtmin();
+
+	struct sigaction act = {
+		.sa_sigaction = enviable_callback,
+		.sa_mask = 0,
+		.sa_flags = SA_SIGINFO,
+	}, oldact;
+
+	if (sigaction(sigrtmin, &act, &oldact) == -1) {
+		maybe_perror("enviable: sigaction");
+		goto err;
+	}
+
+	if ((oldact.sa_flags & SA_SIGINFO) ||
+	    (oldact.sa_handler != SIG_DFL)) {
+		/* Oops. Someone else already claimed a handler! */
+		goto err_sig;
+	}
+
+	int flags = fcntl(fd, F_GETFL);
+	if (flags == -1) {
+		maybe_perror("enviable: fcntl F_GETFL");
+		goto err_sig;
+	}
+	if (fcntl(fd, F_SETFL, flags | O_ASYNC) == -1) {
+		maybe_perror("enviable: fcntl F_SETFL O_ASYNC");
+		goto err_sig;
+	}
+	if (fcntl(fd, F_SETOWN, getpid()) == -1) {
+		maybe_perror("enviable: fcntl F_SETOWN");
+		goto err_sig;
+	}
+	if (fcntl(fd, F_SETSIG, sigrtmin) == -1) {
+		maybe_perror("enviable: fcntl F_SETSIG");
+		goto err_sig;
+	}
+
+	return;
+err_sig:
+	sigaction(sigrtmin, &oldact, NULL);
+err:
+	close(fd);
+}