sd-bus: when connecting to a container AF_UNIX bus, return error

When forking of a child process for connecting to a container, pass
the preicse connection error to the calling process.

We already did this correctly for kdbus busses, let's do so for dbus1
busses, too.

1 files changed, 37 insertions, 13 deletions

diff --git a/src/libsystemd/sd-bus/bus-container.c b/src/libsystemd/sd-bus/bus-container.c
index 56dc086ae2..5c607f49b1 100644
--- a/src/libsystemd/sd-bus/bus-container.c
+++ b/src/libsystemd/sd-bus/bus-container.c
@@ -29,10 +29,12 @@
 #include "bus-container.h"
 
 int bus_container_connect_socket(sd_bus *b) {
+        _cleanup_close_pair_ int pair[2] = { -1, -1 };
         _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, usernsfd = -1, rootfd = -1;
         pid_t child;
         siginfo_t si;
-        int r;
+        int r, error_buf = 0;
+        ssize_t n;
 
         assert(b);
         assert(b->input_fd < 0);
@@ -57,6 +59,9 @@ int bus_container_connect_socket(sd_bus *b) {
 
         bus_socket_setup(b);
 
+        if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, pair) < 0)
+                return -errno;
+
         child = fork();
         if (child < 0)
                 return -errno;
@@ -64,9 +69,11 @@ int bus_container_connect_socket(sd_bus *b) {
         if (child == 0) {
                 pid_t grandchild;
 
+                pair[0] = safe_close(pair[0]);
+
                 r = namespace_enter(pidnsfd, mntnsfd, -1, usernsfd, rootfd);
                 if (r < 0)
-                        _exit(255);
+                        _exit(EXIT_FAILURE);
 
                 /* We just changed PID namespace, however it will only
                  * take effect on the children we now fork. Hence,
@@ -77,16 +84,16 @@ int bus_container_connect_socket(sd_bus *b) {
 
                 grandchild = fork();
                 if (grandchild < 0)
-                        _exit(255);
+                        _exit(EXIT_FAILURE);
 
                 if (grandchild == 0) {
 
                         r = connect(b->input_fd, &b->sockaddr.sa, b->sockaddr_size);
                         if (r < 0) {
-                                if (errno == EINPROGRESS)
-                                        _exit(1);
-
-                                _exit(255);
+                                /* Try to send error up */
+                                error_buf = errno;
+                                (void) write(pair[1], &error_buf, sizeof(error_buf));
+                                _exit(EXIT_FAILURE);
                         }
 
                         _exit(EXIT_SUCCESS);
@@ -94,24 +101,41 @@ int bus_container_connect_socket(sd_bus *b) {
 
                 r = wait_for_terminate(grandchild, &si);
                 if (r < 0)
-                        _exit(255);
+                        _exit(EXIT_FAILURE);
 
                 if (si.si_code != CLD_EXITED)
-                        _exit(255);
+                        _exit(EXIT_FAILURE);
 
                 _exit(si.si_status);
         }
 
+        pair[1] = safe_close(pair[1]);
+
         r = wait_for_terminate(child, &si);
         if (r < 0)
                 return r;
 
+        n = read(pair[0], &error_buf, sizeof(error_buf));
+        if (n < 0)
+                return -errno;
+
+        if (n > 0) {
+                if (n != sizeof(error_buf))
+                        return -EIO;
+
+                if (error_buf < 0)
+                        return -EIO;
+
+                if (error_buf == EINPROGRESS)
+                        return 1;
+
+                if (error_buf > 0)
+                        return -error_buf;
+        }
+
         if (si.si_code != CLD_EXITED)
                 return -EIO;
 
-        if (si.si_status == 1)
-                return 1;
-
         if (si.si_status != EXIT_SUCCESS)
                 return -EIO;
 
@@ -157,7 +181,7 @@ int bus_container_connect_kernel(sd_bus *b) {
         if (r < 0)
                 return r;
 
-        if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) < 0)
+        if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, pair) < 0)
                 return -errno;
 
         child = fork();