Add sandboxed download for the internal downloader

If the SandboxUser configure option is set, the internal downloader
will fork of a child process and drop to the specified user to download
the files.

Signed-off-by: Remi Gacogne <rgacogne@archlinux.org>
Signed-off-by: Allan McRae <allan@archlinux.org>

lib/libalpm/dload.c

@@ -28,6 +28,7 @@
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
 #include <signal.h>
 
 #ifdef HAVE_NETINET_IN_H
@@ -48,6 +49,7 @@
 #include "log.h"
 #include "util.h"
 #include "handle.h"
+#include "sandbox.h"
 
 #ifdef HAVE_LIBCURL
 
@@ -972,6 +974,158 @@ static int curl_download_internal(alpm_handle_t *handle,
 	return ret;
 }
 
+/* Download the requested files by launching a process inside a sandbox.
+ * Returns -1 if an error happened for a required file
+ * Returns 0 if a payload was actually downloaded
+ * Returns 1 if no files were downloaded and all errors were non-fatal
+ */
+static int curl_download_internal_sandboxed(alpm_handle_t *handle,
+		alpm_list_t *payloads /* struct dload_payload */,
+		const char *localpath)
+{
+	int pid, err = 0, ret = -1, callbacks_fd[2];
+	sigset_t oldblock;
+	struct sigaction sa_ign, oldint, oldquit;
+	_alpm_sandbox_callback_context callbacks_ctx;
+
+	sigemptyset(&sa_ign.sa_mask);
+	sa_ign.sa_handler = SIG_IGN;
+	sa_ign.sa_flags=0;
+
+	if(pipe(callbacks_fd) != 0) {
+		return -1;
+	}
+
+	sigaction(SIGINT, &sa_ign, &oldint);
+	sigaction(SIGQUIT, &sa_ign, &oldquit);
+	sigaddset(&sa_ign.sa_mask, SIGCHLD);
+	sigprocmask(SIG_BLOCK, &sa_ign.sa_mask, &oldblock);
+
+	pid = fork();
+	if(pid == -1) {
+		/* fork failed, make sure errno is preserved after cleanup */
+		err = errno;
+	}
+
+	/* child */
+	if(pid == 0) {
+		close(callbacks_fd[0]);
+		fcntl(callbacks_fd[1], F_SETFD, FD_CLOEXEC);
+		callbacks_ctx.callback_pipe = callbacks_fd[1];
+		alpm_option_set_logcb(handle, _alpm_sandbox_cb_log, &callbacks_ctx);
+		alpm_option_set_dlcb(handle, _alpm_sandbox_cb_dl, &callbacks_ctx);
+		alpm_option_set_fetchcb(handle, NULL, NULL);
+		alpm_option_set_eventcb(handle, NULL, NULL);
+		alpm_option_set_questioncb(handle, NULL, NULL);
+		alpm_option_set_progresscb(handle, NULL, NULL);
+
+		/* restore default signal handling in the child */
+		_alpm_reset_signals();
+
+		/* cwd to the download directory */
+		ret = chdir(localpath);
+		if(ret != 0) {
+			handle->pm_errno = ALPM_ERR_NOT_A_DIR;
+			_alpm_log(handle, ALPM_LOG_ERROR, _("could not chdir to download directory %s\n"), localpath);
+			ret = -1;
+		} else {
+			ret = alpm_sandbox_child(handle->sandboxuser);
+			if (ret != 0) {
+				_alpm_log(handle, ALPM_LOG_ERROR, _("switching to sandbox user '%s' failed!\n"), handle->sandboxuser);
+				_Exit(2);
+			}
+
+			ret = curl_download_internal(handle, payloads, localpath);
+		}
+
+		/* pass the result back to the parent */
+		if(ret == 0) {
+			/* a payload was actually downloaded */
+			_Exit(0);
+		}
+		else if(ret == 1) {
+			/* no files were downloaded and all errors were non-fatal */
+			_Exit(1);
+		}
+		else {
+			/* an error happened for a required file */
+			_Exit(2);
+		}
+	}
+
+	/* parent */
+	close(callbacks_fd[1]);
+
+	if(pid != -1)  {
+		bool had_error = false;
+		while(true) {
+			_alpm_sandbox_callback_t callback_type;
+			ssize_t got = read(callbacks_fd[0], &callback_type, sizeof(callback_type));
+			if(got < 0 || (size_t)got != sizeof(callback_type)) {
+				had_error = true;
+				break;
+			}
+
+			if(callback_type == ALPM_SANDBOX_CB_DOWNLOAD) {
+				if(!_alpm_sandbox_process_cb_download(handle, callbacks_fd[0])) {
+					had_error = true;
+					break;
+				}
+			}
+			else if(callback_type == ALPM_SANDBOX_CB_LOG) {
+				if(!_alpm_sandbox_process_cb_log(handle, callbacks_fd[0])) {
+					had_error = true;
+					break;
+				}
+			}
+		}
+
+
+		if(had_error) {
+			kill(pid, SIGTERM);
+		}
+
+		int wret;
+		while((wret = waitpid(pid, &ret, 0)) == -1 && errno == EINTR);
+		if(wret > 0) {
+			if(!WIFEXITED(ret)) {
+				/* the child did not terminate normally */
+				ret = -1;
+			}
+			else {
+				ret = WEXITSTATUS(ret);
+				if(ret != 0) {
+					if(ret == 2) {
+						/* an error happened for a required file, or unexpected exit status */
+						handle->pm_errno = ALPM_ERR_RETRIEVE;
+						ret = -1;
+					}
+					else {
+						handle->pm_errno = ALPM_ERR_RETRIEVE;
+						ret = 1;
+					}
+				}
+			}
+		}
+		else {
+			/* waitpid failed */
+			err = errno;
+		}
+	}
+
+	close(callbacks_fd[0]);
+
+	sigaction(SIGINT, &oldint, NULL);
+	sigaction(SIGQUIT, &oldquit, NULL);
+	sigprocmask(SIG_SETMASK, &oldblock, NULL);
+
+	if(err) {
+		errno = err;
+		ret = -1;
+	}
+	return ret;
+}
+
 #endif
 
 static int payload_download_fetchcb(struct dload_payload *payload,
@@ -1001,7 +1155,11 @@ int _alpm_download(alpm_handle_t *handle,
 {
 	if(handle->fetchcb == NULL) {
 #ifdef HAVE_LIBCURL
-		return curl_download_internal(handle, payloads, localpath);
+		if(handle->sandboxuser) {
+			return curl_download_internal_sandboxed(handle, payloads, localpath);
+		} else {
+			return curl_download_internal(handle, payloads, localpath);
+		}
 #else
 		RET_ERR(handle, ALPM_ERR_EXTERNAL_DOWNLOAD, -1);
 #endif

src/pacman/callback.c

@@ -57,7 +57,7 @@ static alpm_list_t *output = NULL;
 #endif
 
 struct pacman_progress_bar {
-	const char *filename;
+	char *filename;
 	off_t xfered; /* Current amount of transferred data */
 	off_t total_size;
 	size_t downloaded;
@@ -752,7 +752,8 @@ static void init_total_progressbar(void)
 {
 	totalbar = calloc(1, sizeof(struct pacman_progress_bar));
 	assert(totalbar);
-	totalbar->filename = _("Total");
+	totalbar->filename = strdup(_("Total"));
+	assert(totalbar->filename);
 	totalbar->init_time = get_time_ms();
 	totalbar->total_size = list_total;
 	totalbar->howmany = list_total_pkgs;
@@ -889,7 +890,8 @@ static void dload_init_event(const char *filename, alpm_download_event_init_t *d
 
 	struct pacman_progress_bar *bar = calloc(1, sizeof(struct pacman_progress_bar));
 	assert(bar);
-	bar->filename = filename;
+	bar->filename = strdup(filename);
+	assert(bar->filename);
 	bar->init_time = get_time_ms();
 	bar->rate = 0.0;
 	multibar_ui.active_downloads = alpm_list_add(multibar_ui.active_downloads, bar);
@@ -1094,6 +1096,7 @@ static void dload_complete_event(const char *filename, alpm_download_event_compl
 			multibar_ui.active_downloads = alpm_list_remove_item(
 				multibar_ui.active_downloads, head);
 			free(head);
+			free(j->filename);
 			free(j);
 		} else {
 			break;