pstree: Restore task group leader when inherit SID

The current behaviour of CRIU is to inherit the group leader of the
parent process when migrating a session leader (with --shell-job).
However, it is possible for a process to be group leader without being
a session leader (e.g. a shell process). In this case CRIU should
restore the original group ID of the process and inherit only the
session ID.

Closes #593
Signed-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>

criu/pstree.c

@@ -367,22 +367,31 @@ static int prepare_pstree_for_shell_job(pid_t pid)
 	 */
 
 	old_sid = root_item->sid;
-	old_gid = root_item->pgid;
 
-	pr_info("Migrating process tree (GID %d->%d SID %d->%d)\n",
-		old_gid, current_gid, old_sid, current_sid);
+	pr_info("Migrating process tree (SID %d->%d)\n",
+		old_sid, current_sid);
 
 	for_each_pstree_item(pi) {
-		if (pi->pgid == old_gid)
-			pi->pgid = current_gid;
 		if (pi->sid == old_sid)
 			pi->sid = current_sid;
 	}
 
-	if (lookup_create_item(current_sid) == NULL)
-		return -1;
-	if (lookup_create_item(current_gid) == NULL)
-		return -1;
+	old_gid = root_item->pgid;
+	if (old_gid != vpid(root_item)) {
+		if (lookup_create_item(current_sid) == NULL)
+			return -1;
+
+		pr_info("Migrating process tree (GID %d->%d)\n",
+			old_gid, current_gid);
+
+		for_each_pstree_item(pi) {
+			if (pi->pgid == old_gid)
+				pi->pgid = current_gid;
+		}
+
+		if (lookup_create_item(current_gid) == NULL)
+			return -1;
+	}
 
 	return 0;
 }

criu/tty.c

@@ -1068,10 +1068,15 @@ out:
 		 * the process which keeps the master peer.
 		 */
 		if (root_item->sid != vpid(root_item)) {
-			pr_debug("Restore inherited group %d\n",
-				 getpgid(getppid()));
-			if (tty_set_prgp(fd, getpgid(getppid())))
-				goto err;
+			if (root_item->pgid == vpid(root_item)) {
+				if (tty_set_prgp(fd, root_item->pgid))
+					goto err;
+			} else {
+				pr_debug("Restore inherited group %d\n",
+					getpgid(getppid()));
+				if (tty_set_prgp(fd, getpgid(getppid())))
+					goto err;
+			}
 		}
 	}