[pacman-dev] [PATCH] use sockets for scriptlet/hook communication

[Andrew Gregory]

If a scriptlet/hook dies at the wrong moment it can trigger SIGPIPE,
terminating the process.  For pipes, there is no way to prevent SIGPIPE
other than ignoring it process-wide.  This can have unintended
consequences in a multi-threaded process.  Using send(2) with sockets,
however, allows ignoring SIGPIPE on a per-call basis, leaving other
threads able to make use of SIGPIPE.

Signed-off-by: Andrew Gregory <andrew.gregory.8 at gmail.com>
---
 lib/libalpm/util.c | 17 ++++-------------
 1 file changed, 4 insertions(+), 13 deletions(-)

diff --git a/lib/libalpm/util.c b/lib/libalpm/util.c
index 58efa5c7..5a7f2c87 100644
--- a/lib/libalpm/util.c
+++ b/lib/libalpm/util.c
@@ -30,6 +30,7 @@
 #include <errno.h>
 #include <limits.h>
 #include <sys/wait.h>
+#include <sys/socket.h>
 #include <fnmatch.h>
 #include <poll.h>
 
@@ -463,7 +464,6 @@ static int _alpm_chroot_write_to_child(alpm_handle_t *handle, int fd,
 		_alpm_cb_io out_cb, void *cb_ctx)
 {
 	ssize_t nwrite;
-	struct sigaction newaction, oldaction;
 
 	if(*buf_size == 0) {
 		/* empty buffer, ask the callback for more */
@@ -473,16 +473,7 @@ static int _alpm_chroot_write_to_child(alpm_handle_t *handle, int fd,
 		}
 	}
 
-	/* ignore SIGPIPE in case the pipe has been closed */
-	newaction.sa_handler = SIG_IGN;
-	sigemptyset(&newaction.sa_mask);
-	newaction.sa_flags = 0;
-	sigaction(SIGPIPE, &newaction, &oldaction);
-
-	nwrite = write(fd, buf, *buf_size);
-
-	/* restore previous SIGPIPE handler */
-	sigaction(SIGPIPE, &oldaction, NULL);
+	nwrite = send(fd, buf, *buf_size, MSG_NOSIGNAL);
 
 	if(nwrite != -1) {
 		/* write was successful, remove the written data from the buffer */
@@ -592,13 +583,13 @@ int _alpm_run_chroot(alpm_handle_t *handle, const char *cmd, char *const argv[],
 	/* Flush open fds before fork() to avoid cloning buffers */
 	fflush(NULL);
 
-	if(pipe(child2parent_pipefd) == -1) {
+	if(socketpair(AF_UNIX, SOCK_STREAM, 0, child2parent_pipefd) == -1) {
 		_alpm_log(handle, ALPM_LOG_ERROR, _("could not create pipe (%s)\n"), strerror(errno));
 		retval = 1;
 		goto cleanup;
 	}
 
-	if(pipe(parent2child_pipefd) == -1) {
+	if(socketpair(AF_UNIX, SOCK_STREAM, 0, parent2child_pipefd) == -1) {
 		_alpm_log(handle, ALPM_LOG_ERROR, _("could not create pipe (%s)\n"), strerror(errno));
 		retval = 1;
 		goto cleanup;
-- 
2.12.2