hscript: bootloader: Take 100% control of efivarfs

We're the executor, we can just commandeer the entire thing, host system
included.  There is very low likelihood of damage to a host system because
we are use umount instead of making the host r/w.

The only thing that could break is `systemctl reboot --firmware`, or a
host-side upgrade of GRUB that somehow changes the path of the EFI stub.

Both of these are almost impossible to encounter on a host that is actually
running the executor.  However, encountering a broken read-only efivarfs
seems to be VERY common in the Installation Environment.

Fixes: ab212730bd ("hscript: bootloader: Set rdwr on 'real' efivarfs")

1 files changed, 6 insertions, 24 deletions

diff --git a/hscript/meta.cc b/hscript/meta.cc
index c4a4070..e8bddd8 100644
--- a/hscript/meta.cc
+++ b/hscript/meta.cc
@@ -18,8 +18,6 @@
 #ifdef HAS_INSTALL_ENV
 #   include <cstring>
 #   include <sys/mount.h>
-#   include <sys/syscall.h>  /* SYS_mount_setattr */
-#   include <linux/mount.h>  /* MOUNT_ATTR_RDONLY, struct mount_attr */
 #   include "util/filesystem.hh"
 #endif /* HAS_INSTALL_ENV */
 #include <unistd.h>         /* access - used by tz code even in RT env */
@@ -861,31 +859,17 @@ bool Bootloader::execute() const {
         const auto efipath{script->targetDirectory() +
                            "/sys/firmware/efi/efivars"};
         bool efivarfs = false;
-        bool umount = false;
         if(fs::exists(efipath)) {
+            /* if it isn't already mounted, that's fine */
+            umount(efipath.c_str());
+            /* we have to umount all efivarfs ro mounts to make any rw */
+            umount("/sys/firmware/efi/efivars");
             if(mount("efivarfs", efipath.c_str(), "efivarfs", MS_NOEXEC |
                      MS_NODEV | MS_NOSUID | MS_RELATIME, nullptr) != 0) {
-                if(errno == EBUSY) {
-                    struct mount_attr attr = {};
-                    attr.attr_clr = MS_RDONLY;
-                    /* set rdwr on parent mount first
-                     * if this fails we can still try the target mount */
-                    syscall(SYS_mount_setattr, -1, "/sys/firmware/efi/efivars",
-                            0, &attr, sizeof(attr));
-                    if(syscall(SYS_mount_setattr, -1, efipath.c_str(), 0,
-                               &attr, sizeof(attr)) != 0) {
-                        output_error(pos, "bootloader: failed to make NVRAM read/write",
-                                     ::strerror(errno));
-                    } else {
-                        efivarfs = true;
-                    }
-                } else {
-                    output_error(pos, "bootloader: failed to mount efivarfs",
-                                 ::strerror(errno));
-                }
+                output_error(pos, "bootloader: failed to mount efivarfs",
+                             ::strerror(errno));
             } else {
                 efivarfs = true;
-                umount = true;  /* We mounted it ourselves. */
             }
         }
 
@@ -906,8 +890,6 @@ bool Bootloader::execute() const {
             return false;
         }
 
-        /* done, back to r/o */
-        if(umount) ::umount(efipath.c_str());
         goto updateboot;
 #endif  /* HAS_INSTALL_ENV */
     }