image: ISO backend: Bail out on umount failure

Only if the error is EBUSY - which implies there *is* a filesystem mounted
at the specified path - we treat umount as an error and stop.  This should
prevent /dev from being erased host-side.

1 files changed, 8 insertions, 2 deletions

diff --git a/image/backends/iso.cc b/image/backends/iso.cc
index 00f5ae4..9be8029 100644
--- a/image/backends/iso.cc
+++ b/image/backends/iso.cc
@@ -203,8 +203,14 @@ public:
              */
             for(const std::string mount : {"dev", "proc", "sys"}) {
                 const std::string path = this->ir_dir + "/target/" + mount;
-                if(::umount(path.c_str()) == EBUSY) {
-                    run_command("umount", {"-R", path});
+                if(::umount(path.c_str()) == -1) {
+                    /* if EBUSY, it will remain mounted when we fs::remove_all
+                     * which will affect the host's environment.  Bail out. */
+                    if(errno == EBUSY &&
+                       run_command("umount", {"-R", path}) != 0) {
+                        output_error("CD backend", "could not umount " + path);
+                        return FS_ERROR;
+                    }
                 }
             }
             fs::remove_all(this->ir_dir, ec);